Thread
Commits
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doc: Fix description about pg_stat_statements.track_planning.
- 306c5e05e20f 13.4 landed
- e48f2afee631 14.0 landed
- 9d2a7757347c 15.0 landed
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doc: Add note about possible performance overhead by enabling track_planning.
- da6b6ff95bca 13.0 landed
- 321fa6a4a26c 14.0 landed
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Change default of pg_stat_statements.track_planning to off.
- 8d459762b103 13.0 landed
- d1763ea8c9c3 14.0 landed
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track_planning causing performance regression
Tharakan, Robins <tharar@amazon.com> — 2020-06-29T05:48:35Z
Hi, During fully-cached SELECT-only test using pgbench, Postgres v13Beta1 shows ~45% performance drop [2] at high DB connection counts (when compared with v12.3) Disabling pg_stat_statements.track_planning (which is 'On' by default) brings the TPS numbers up to v12.3 levels. The inflection point (in this test-case) is 128 Connections, beyond which the TPS numbers are consistently low. Looking at the mailing list [1], this issue didn't surface earlier possibly since the regression is trivial at low connection counts. It would be great if this could be optimized further, or track_planning disabled (by default) so as to not trip users upgrading from v12 with pg_stat_statement enabled (but otherwise not particularly interested in track_planning). These are some details around the above test: pgbench: scale - 100 / threads - 16 test-duration - 30s each server - 96 vCPUs / 768GB - r5.24xl (AWS EC2 instance) client - 72 vCPUs / 144GB - c5.18xl (AWS EC2 instance) (co-located with the DB server - Same AZ) v12 - REL_12_STABLE (v12.3) v13Beta1 - REL_13_STABLE (v13Beta1) max_connections = 10000 shared_preload_libraries = 'pg_stat_statements' shared_buffers 128MB Reference: 1) https://www.postgresql.org/message-id/1554150919882-0.post%40n3.nabble.com 2) Fully-cached-select-only TPS drops >= 128 connections. Conn v12.3 v13Beta1 v13Beta1 (track_planning=off) 1 6,764 6,734 6,905 2 14,978 14,961 15,316 4 31,641 32,012 36,961 8 71,989 68,848 69,204 16 129,056 131,157 132,773 32 231,910 226,718 253,316 64 381,778 371,782 385,402 128 534,661 ====> 353,944 539,231 256 636,794 ====> 248,825 643,631 512 574,447 ====> 213,033 555,099 768 493,912 ====> 214,801 502,014 1024 484,993 ====> 222,492 490,716 1280 480,571 ====> 223,296 483,843 1536 475,030 ====> 228,137 477,153 1792 472,145 ====> 229,027 474,423 2048 471,385 ====> 228,665 470,238 3) perf - v13Beta1 - 88.38% 0.17% postgres postgres [.] PostgresMain - 88.21% PostgresMain - 80.09% exec_simple_query - 25.34% pg_plan_queries - 25.28% pg_plan_query - 25.21% pgss_planner - 14.36% pgss_store + 13.54% s_lock + 10.71% standard_planner + 18.29% PortalRun - 15.12% PortalDrop - 14.73% PortalCleanup - 13.78% pgss_ExecutorEnd - 13.72% pgss_store + 12.83% s_lock 0.72% standard_ExecutorEnd + 6.18% PortalStart + 4.86% pg_analyze_and_rewrite + 3.52% GetTransactionSnapshot + 2.56% pg_parse_query + 1.83% finish_xact_command 0.51% start_xact_command + 3.93% pq_getbyte + 3.40% ReadyForQuery 4) perf - v12.3 v12.3 - 84.32% 0.21% postgres postgres [.] PostgresMain - 84.11% PostgresMain - 72.56% exec_simple_query + 26.71% PortalRun - 15.33% pg_plan_queries - 15.29% pg_plan_query + 15.21% standard_planner + 7.81% PortalStart + 6.76% pg_analyze_and_rewrite + 4.37% GetTransactionSnapshot + 3.69% pg_parse_query - 2.96% PortalDrop - 2.42% PortalCleanup - 1.35% pgss_ExecutorEnd - 1.22% pgss_store 0.57% s_lock 0.77% standard_ExecutorEnd + 2.16% finish_xact_command + 0.78% start_xact_command + 0.59% pg_rewrite_query + 5.67% pq_getbyte + 4.73% ReadyForQuery - robins -
Re: track_planning causing performance regression
Julien Rouhaud <rjuju123@gmail.com> — 2020-06-29T07:05:18Z
Hi, On Mon, Jun 29, 2020 at 7:49 AM Tharakan, Robins <tharar@amazon.com> wrote: > > During fully-cached SELECT-only test using pgbench, Postgres v13Beta1 shows > ~45% performance drop [2] at high DB connection counts (when compared with v12.3) > > Disabling pg_stat_statements.track_planning (which is 'On' by default) > brings the TPS numbers up to v12.3 levels. > > The inflection point (in this test-case) is 128 Connections, beyond which the > TPS numbers are consistently low. Looking at the mailing list [1], this issue > didn't surface earlier possibly since the regression is trivial at low connection counts. > > It would be great if this could be optimized further, or track_planning > disabled (by default) so as to not trip users upgrading from v12 with pg_stat_statement > enabled (but otherwise not particularly interested in track_planning). > > These are some details around the above test: > > pgbench: scale - 100 / threads - 16 > test-duration - 30s each > server - 96 vCPUs / 768GB - r5.24xl (AWS EC2 instance) > client - 72 vCPUs / 144GB - c5.18xl (AWS EC2 instance) (co-located with the DB server - Same AZ) > v12 - REL_12_STABLE (v12.3) > v13Beta1 - REL_13_STABLE (v13Beta1) > max_connections = 10000 > shared_preload_libraries = 'pg_stat_statements' > shared_buffers 128MB I can't reproduce this on my laptop, but I can certainly believe that running the same 3 queries using more connections than available cores will lead to extra overhead. I disagree with the conclusion though. It seems to me that if you really have this workload that consists in these few queries and want to get better performance, you'll anyway use a connection pooler and/or use prepared statements, which will make this overhead disappear entirely, and will also yield an even bigger performance improvement. A quick test using pgbench -M prepared, with track_planning enabled, with still way too many connections already shows a 25% improvement over the -M simple without track_planning.
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-06-29T08:55:28Z
On 2020/06/29 16:05, Julien Rouhaud wrote: > Hi, > > On Mon, Jun 29, 2020 at 7:49 AM Tharakan, Robins <tharar@amazon.com> wrote: >> >> During fully-cached SELECT-only test using pgbench, Postgres v13Beta1 shows Thanks for the benchmark! >> ~45% performance drop [2] at high DB connection counts (when compared with v12.3) That's bad :( >> >> Disabling pg_stat_statements.track_planning (which is 'On' by default) >> brings the TPS numbers up to v12.3 levels. >> >> The inflection point (in this test-case) is 128 Connections, beyond which the >> TPS numbers are consistently low. Looking at the mailing list [1], this issue >> didn't surface earlier possibly since the regression is trivial at low connection counts. >> >> It would be great if this could be optimized further, or track_planning >> disabled (by default) so as to not trip users upgrading from v12 with pg_stat_statement >> enabled (but otherwise not particularly interested in track_planning). Your benchmark result seems to suggest that the cause of the problem is the contention of per-query spinlock in pgss_store(). Right? This lock contention is likely to happen when multiple sessions run the same queries. One idea to reduce that lock contention is to separate per-query spinlock into two; one is for planning, and the other is for execution. pgss_store() determines which lock to use based on the given "kind" argument. To make this idea work, also every pgss counters like shared_blks_hit need to be separated into two, i.e., for planning and execution. >> These are some details around the above test: >> >> pgbench: scale - 100 / threads - 16 >> test-duration - 30s each >> server - 96 vCPUs / 768GB - r5.24xl (AWS EC2 instance) >> client - 72 vCPUs / 144GB - c5.18xl (AWS EC2 instance) (co-located with the DB server - Same AZ) >> v12 - REL_12_STABLE (v12.3) >> v13Beta1 - REL_13_STABLE (v13Beta1) >> max_connections = 10000 >> shared_preload_libraries = 'pg_stat_statements' >> shared_buffers 128MB > > I can't reproduce this on my laptop, but I can certainly believe that > running the same 3 queries using more connections than available cores > will lead to extra overhead. > > I disagree with the conclusion though. It seems to me that if you > really have this workload that consists in these few queries and want > to get better performance, you'll anyway use a connection pooler > and/or use prepared statements, which will make this overhead > disappear entirely, and will also yield an even bigger performance > improvement. A quick test using pgbench -M prepared, with > track_planning enabled, with still way too many connections already > shows a 25% improvement over the -M simple without track_planning. I understand your point. But IMO the default setting basically should be safer value, i.e., off at least until the problem disappears. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Julien Rouhaud <rjuju123@gmail.com> — 2020-06-29T09:17:14Z
On Mon, Jun 29, 2020 at 10:55 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > On 2020/06/29 16:05, Julien Rouhaud wrote: > > On Mon, Jun 29, 2020 at 7:49 AM Tharakan, Robins <tharar@amazon.com> wrote: > >> > >> During fully-cached SELECT-only test using pgbench, Postgres v13Beta1 shows > > Thanks for the benchmark! > > > >> ~45% performance drop [2] at high DB connection counts (when compared with v12.3) > > That's bad :( > > > >> > >> Disabling pg_stat_statements.track_planning (which is 'On' by default) > >> brings the TPS numbers up to v12.3 levels. > >> > >> The inflection point (in this test-case) is 128 Connections, beyond which the > >> TPS numbers are consistently low. Looking at the mailing list [1], this issue > >> didn't surface earlier possibly since the regression is trivial at low connection counts. > >> > >> It would be great if this could be optimized further, or track_planning > >> disabled (by default) so as to not trip users upgrading from v12 with pg_stat_statement > >> enabled (but otherwise not particularly interested in track_planning). > > Your benchmark result seems to suggest that the cause of the problem is > the contention of per-query spinlock in pgss_store(). Right? > This lock contention is likely to happen when multiple sessions run > the same queries. > > One idea to reduce that lock contention is to separate per-query spinlock > into two; one is for planning, and the other is for execution. pgss_store() > determines which lock to use based on the given "kind" argument. > To make this idea work, also every pgss counters like shared_blks_hit > need to be separated into two, i.e., for planning and execution. This can probably remove some overhead, but won't it eventually hit the same issue when multiple connections try to plan the same query, given the number of different queries and very low execution runtime? It'll also quite increase the shared memory consumption. I'm wondering if we could instead use atomics to store the counters. The only downside is that we won't guarantee per-row consistency anymore, which may be problematic.
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-06-29T09:38:17Z
On 2020/06/29 18:17, Julien Rouhaud wrote: > On Mon, Jun 29, 2020 at 10:55 AM Fujii Masao > <masao.fujii@oss.nttdata.com> wrote: >> >> On 2020/06/29 16:05, Julien Rouhaud wrote: >>> On Mon, Jun 29, 2020 at 7:49 AM Tharakan, Robins <tharar@amazon.com> wrote: >>>> >>>> During fully-cached SELECT-only test using pgbench, Postgres v13Beta1 shows >> >> Thanks for the benchmark! >> >> >>>> ~45% performance drop [2] at high DB connection counts (when compared with v12.3) >> >> That's bad :( >> >> >>>> >>>> Disabling pg_stat_statements.track_planning (which is 'On' by default) >>>> brings the TPS numbers up to v12.3 levels. >>>> >>>> The inflection point (in this test-case) is 128 Connections, beyond which the >>>> TPS numbers are consistently low. Looking at the mailing list [1], this issue >>>> didn't surface earlier possibly since the regression is trivial at low connection counts. >>>> >>>> It would be great if this could be optimized further, or track_planning >>>> disabled (by default) so as to not trip users upgrading from v12 with pg_stat_statement >>>> enabled (but otherwise not particularly interested in track_planning). >> >> Your benchmark result seems to suggest that the cause of the problem is >> the contention of per-query spinlock in pgss_store(). Right? >> This lock contention is likely to happen when multiple sessions run >> the same queries. >> >> One idea to reduce that lock contention is to separate per-query spinlock >> into two; one is for planning, and the other is for execution. pgss_store() >> determines which lock to use based on the given "kind" argument. >> To make this idea work, also every pgss counters like shared_blks_hit >> need to be separated into two, i.e., for planning and execution. > > This can probably remove some overhead, but won't it eventually hit > the same issue when multiple connections try to plan the same query, > given the number of different queries and very low execution runtime? Yes. But maybe we can expect that the idea would improve the performance to the near same level as v12? > It'll also quite increase the shared memory consumption. Yes. > I'm wondering if we could instead use atomics to store the counters. > The only downside is that we won't guarantee per-row consistency > anymore, which may be problematic. Yeah, we can consider more improvements against this issue. But I'm afraid these (maybe including my idea) basically should be items for v14... Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Julien Rouhaud <rjuju123@gmail.com> — 2020-06-29T09:53:27Z
On Mon, Jun 29, 2020 at 11:38 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > >> Your benchmark result seems to suggest that the cause of the problem is > >> the contention of per-query spinlock in pgss_store(). Right? > >> This lock contention is likely to happen when multiple sessions run > >> the same queries. > >> > >> One idea to reduce that lock contention is to separate per-query spinlock > >> into two; one is for planning, and the other is for execution. pgss_store() > >> determines which lock to use based on the given "kind" argument. > >> To make this idea work, also every pgss counters like shared_blks_hit > >> need to be separated into two, i.e., for planning and execution. > > > > This can probably remove some overhead, but won't it eventually hit > > the same issue when multiple connections try to plan the same query, > > given the number of different queries and very low execution runtime? > > Yes. But maybe we can expect that the idea would improve > the performance to the near same level as v12? A POC patch should be easy to do and see how much it solves this problem. However I'm not able to reproduce the issue, and IMHO unless we specifically want to be able to distinguish planner-time counters from execution-time counters, I'd prefer to disable track_planning by default than going this way, so that users with a sane usage won't have to suffer from a memory increase. > > I'm wondering if we could instead use atomics to store the counters. > > The only downside is that we won't guarantee per-row consistency > > anymore, which may be problematic. > > Yeah, we can consider more improvements against this issue. > But I'm afraid these (maybe including my idea) basically should > be items for v14... Yes, that's clearly not something I'd vote to push in v13 at this point.
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-06-29T09:56:02Z
On 2020/06/29 18:53, Julien Rouhaud wrote: > On Mon, Jun 29, 2020 at 11:38 AM Fujii Masao > <masao.fujii@oss.nttdata.com> wrote: >> >>>> Your benchmark result seems to suggest that the cause of the problem is >>>> the contention of per-query spinlock in pgss_store(). Right? >>>> This lock contention is likely to happen when multiple sessions run >>>> the same queries. >>>> >>>> One idea to reduce that lock contention is to separate per-query spinlock >>>> into two; one is for planning, and the other is for execution. pgss_store() >>>> determines which lock to use based on the given "kind" argument. >>>> To make this idea work, also every pgss counters like shared_blks_hit >>>> need to be separated into two, i.e., for planning and execution. >>> >>> This can probably remove some overhead, but won't it eventually hit >>> the same issue when multiple connections try to plan the same query, >>> given the number of different queries and very low execution runtime? >> >> Yes. But maybe we can expect that the idea would improve >> the performance to the near same level as v12? > > A POC patch should be easy to do and see how much it solves this > problem. However I'm not able to reproduce the issue, and IMHO unless > we specifically want to be able to distinguish planner-time counters > from execution-time counters, I'd prefer to disable track_planning by > default than going this way, so that users with a sane usage won't > have to suffer from a memory increase. Agreed. +1 to change that default to off. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-06-29T11:14:34Z
On 2020/06/29 18:56, Fujii Masao wrote: > > > On 2020/06/29 18:53, Julien Rouhaud wrote: >> On Mon, Jun 29, 2020 at 11:38 AM Fujii Masao >> <masao.fujii@oss.nttdata.com> wrote: >>> >>>>> Your benchmark result seems to suggest that the cause of the problem is >>>>> the contention of per-query spinlock in pgss_store(). Right? >>>>> This lock contention is likely to happen when multiple sessions run >>>>> the same queries. >>>>> >>>>> One idea to reduce that lock contention is to separate per-query spinlock >>>>> into two; one is for planning, and the other is for execution. pgss_store() >>>>> determines which lock to use based on the given "kind" argument. >>>>> To make this idea work, also every pgss counters like shared_blks_hit >>>>> need to be separated into two, i.e., for planning and execution. >>>> >>>> This can probably remove some overhead, but won't it eventually hit >>>> the same issue when multiple connections try to plan the same query, >>>> given the number of different queries and very low execution runtime? >>> >>> Yes. But maybe we can expect that the idea would improve >>> the performance to the near same level as v12? >> >> A POC patch should be easy to do and see how much it solves this >> problem. However I'm not able to reproduce the issue, and IMHO unless >> we specifically want to be able to distinguish planner-time counters >> from execution-time counters, I'd prefer to disable track_planning by >> default than going this way, so that users with a sane usage won't >> have to suffer from a memory increase. > > Agreed. +1 to change that default to off. Attached patch does this. I also add the following into the description about each *_plan_time column in the docs. IMO this is helpful for users when they see that those columns report zero by default and try to understand why. (if <varname>pg_stat_statements.track_planning</varname> is enabled, otherwise zero) Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Julien Rouhaud <rjuju123@gmail.com> — 2020-06-29T11:55:53Z
On Mon, Jun 29, 2020 at 1:14 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > On 2020/06/29 18:56, Fujii Masao wrote: > > > > > > On 2020/06/29 18:53, Julien Rouhaud wrote: > >> On Mon, Jun 29, 2020 at 11:38 AM Fujii Masao > >> <masao.fujii@oss.nttdata.com> wrote: > >>> > >>>>> Your benchmark result seems to suggest that the cause of the problem is > >>>>> the contention of per-query spinlock in pgss_store(). Right? > >>>>> This lock contention is likely to happen when multiple sessions run > >>>>> the same queries. > >>>>> > >>>>> One idea to reduce that lock contention is to separate per-query spinlock > >>>>> into two; one is for planning, and the other is for execution. pgss_store() > >>>>> determines which lock to use based on the given "kind" argument. > >>>>> To make this idea work, also every pgss counters like shared_blks_hit > >>>>> need to be separated into two, i.e., for planning and execution. > >>>> > >>>> This can probably remove some overhead, but won't it eventually hit > >>>> the same issue when multiple connections try to plan the same query, > >>>> given the number of different queries and very low execution runtime? > >>> > >>> Yes. But maybe we can expect that the idea would improve > >>> the performance to the near same level as v12? > >> > >> A POC patch should be easy to do and see how much it solves this > >> problem. However I'm not able to reproduce the issue, and IMHO unless > >> we specifically want to be able to distinguish planner-time counters > >> from execution-time counters, I'd prefer to disable track_planning by > >> default than going this way, so that users with a sane usage won't > >> have to suffer from a memory increase. > > > > Agreed. +1 to change that default to off. > > Attached patch does this. Patch looks good to me. > I also add the following into the description about each *_plan_time column > in the docs. IMO this is helpful for users when they see that those columns > report zero by default and try to understand why. > > (if <varname>pg_stat_statements.track_planning</varname> is enabled, otherwise zero) +1 Do you intend to wait for other input before pushing? FWIW I'm still not convinced that the exposed problem is representative of any realistic workload. I of course entirely agree with the other documentation changes.
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Re: track_planning causing performance regression
Ants Aasma <ants@cybertec.at> — 2020-06-29T13:23:41Z
On Mon, 29 Jun 2020 at 12:17, Julien Rouhaud <rjuju123@gmail.com> wrote: > On Mon, Jun 29, 2020 at 10:55 AM Fujii Masao > <masao.fujii@oss.nttdata.com> wrote: > > > > On 2020/06/29 16:05, Julien Rouhaud wrote: > > > On Mon, Jun 29, 2020 at 7:49 AM Tharakan, Robins <tharar@amazon.com> > wrote: > > >> > > >> During fully-cached SELECT-only test using pgbench, Postgres v13Beta1 > shows > > > > Thanks for the benchmark! > > > > > > >> ~45% performance drop [2] at high DB connection counts (when compared > with v12.3) > > > > That's bad :( > > > > > > >> > > >> Disabling pg_stat_statements.track_planning (which is 'On' by default) > > >> brings the TPS numbers up to v12.3 levels. > > >> > > >> The inflection point (in this test-case) is 128 Connections, beyond > which the > > >> TPS numbers are consistently low. Looking at the mailing list [1], > this issue > > >> didn't surface earlier possibly since the regression is trivial at > low connection counts. > > >> > > >> It would be great if this could be optimized further, or > track_planning > > >> disabled (by default) so as to not trip users upgrading from v12 with > pg_stat_statement > > >> enabled (but otherwise not particularly interested in track_planning). > > > > Your benchmark result seems to suggest that the cause of the problem is > > the contention of per-query spinlock in pgss_store(). Right? > > This lock contention is likely to happen when multiple sessions run > > the same queries. > > > > One idea to reduce that lock contention is to separate per-query spinlock > > into two; one is for planning, and the other is for execution. > pgss_store() > > determines which lock to use based on the given "kind" argument. > > To make this idea work, also every pgss counters like shared_blks_hit > > need to be separated into two, i.e., for planning and execution. > > This can probably remove some overhead, but won't it eventually hit > the same issue when multiple connections try to plan the same query, > given the number of different queries and very low execution runtime? > It'll also quite increase the shared memory consumption. > > I'm wondering if we could instead use atomics to store the counters. > The only downside is that we won't guarantee per-row consistency > anymore, which may be problematic. > The problem looks to be that spinlocks are terrible with overloaded CPU and a contended spinlock. A process holding the spinlock might easily get scheduled out leading to excessive spinning by everybody. I think a simple thing to try would be to replace the spinlock with LWLock. I did a prototype patch that replaces spinlocks with futexes, but was not able to find a workload where it mattered. We have done a great job at eliminating spinlocks from contended code paths. Robins, perhaps you could try it to see if it reduces the regression you are observing. The patch is against v13 stable branch. -- Ants Aasma Senior Database Engineerwww.cybertec-postgresql.com
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Re: track_planning causing performance regression
Peter Geoghegan <pg@bowt.ie> — 2020-06-29T22:23:49Z
On Mon, Jun 29, 2020 at 1:55 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > I disagree with the conclusion though. It seems to me that if you > > really have this workload that consists in these few queries and want > > to get better performance, you'll anyway use a connection pooler > > and/or use prepared statements, which will make this overhead > > disappear entirely, and will also yield an even bigger performance > > improvement. A quick test using pgbench -M prepared, with > > track_planning enabled, with still way too many connections already > > shows a 25% improvement over the -M simple without track_planning. > > I understand your point. But IMO the default setting basically should > be safer value, i.e., off at least until the problem disappears. +1 -- this regression seems unacceptable to me. -- Peter Geoghegan
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Re: track_planning causing performance regression
Peter Geoghegan <pg@bowt.ie> — 2020-06-29T22:29:06Z
On Mon, Jun 29, 2020 at 3:23 PM Peter Geoghegan <pg@bowt.ie> wrote: > +1 -- this regression seems unacceptable to me. I added an open item to track this. Thanks -- Peter Geoghegan
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Re: track_planning causing performance regression
Andres Freund <andres@anarazel.de> — 2020-06-29T23:00:19Z
Hi, On 2020-06-29 09:05:18 +0200, Julien Rouhaud wrote: > I can't reproduce this on my laptop, but I can certainly believe that > running the same 3 queries using more connections than available cores > will lead to extra overhead. > I disagree with the conclusion though. It seems to me that if you > really have this workload that consists in these few queries and want > to get better performance, you'll anyway use a connection pooler > and/or use prepared statements, which will make this overhead > disappear entirely, and will also yield an even bigger performance > improvement. It's an extremely common to have have times where there's more active queries than CPUs. And a pooler won't avoid that fully, at least not without drastically reducing overall throughput. Greetings, Andres Freund
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Re: track_planning causing performance regression
Andres Freund <andres@anarazel.de> — 2020-06-29T23:10:15Z
Hi, On 2020-06-29 17:55:28 +0900, Fujii Masao wrote: > One idea to reduce that lock contention is to separate per-query spinlock > into two; one is for planning, and the other is for execution. pgss_store() > determines which lock to use based on the given "kind" argument. > To make this idea work, also every pgss counters like shared_blks_hit > need to be separated into two, i.e., for planning and execution. I suspect that the best thing would be to just turn the spinlock into an lwlock. Spinlocks deal terribly with contention. I suspect it'd solve the performance issue entirely. And it might even be possible, further down the line, to just use a shared lock, and use atomics for the counters. Greetings, Andres Freund
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-06-30T05:43:39Z
On 2020/06/29 22:23, Ants Aasma wrote: > On Mon, 29 Jun 2020 at 12:17, Julien Rouhaud <rjuju123@gmail.com <mailto:rjuju123@gmail.com>> wrote: > > On Mon, Jun 29, 2020 at 10:55 AM Fujii Masao > <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> wrote: > > > > On 2020/06/29 16:05, Julien Rouhaud wrote: > > > On Mon, Jun 29, 2020 at 7:49 AM Tharakan, Robins <tharar@amazon.com <mailto:tharar@amazon.com>> wrote: > > >> > > >> During fully-cached SELECT-only test using pgbench, Postgres v13Beta1 shows > > > > Thanks for the benchmark! > > > > > > >> ~45% performance drop [2] at high DB connection counts (when compared with v12.3) > > > > That's bad :( > > > > > > >> > > >> Disabling pg_stat_statements.track_planning (which is 'On' by default) > > >> brings the TPS numbers up to v12.3 levels. > > >> > > >> The inflection point (in this test-case) is 128 Connections, beyond which the > > >> TPS numbers are consistently low. Looking at the mailing list [1], this issue > > >> didn't surface earlier possibly since the regression is trivial at low connection counts. > > >> > > >> It would be great if this could be optimized further, or track_planning > > >> disabled (by default) so as to not trip users upgrading from v12 with pg_stat_statement > > >> enabled (but otherwise not particularly interested in track_planning). > > > > Your benchmark result seems to suggest that the cause of the problem is > > the contention of per-query spinlock in pgss_store(). Right? > > This lock contention is likely to happen when multiple sessions run > > the same queries. > > > > One idea to reduce that lock contention is to separate per-query spinlock > > into two; one is for planning, and the other is for execution. pgss_store() > > determines which lock to use based on the given "kind" argument. > > To make this idea work, also every pgss counters like shared_blks_hit > > need to be separated into two, i.e., for planning and execution. > > This can probably remove some overhead, but won't it eventually hit > the same issue when multiple connections try to plan the same query, > given the number of different queries and very low execution runtime? > It'll also quite increase the shared memory consumption. > > I'm wondering if we could instead use atomics to store the counters. > The only downside is that we won't guarantee per-row consistency > anymore, which may be problematic. > > > > The problem looks to be that spinlocks are terrible with overloaded CPU and a contended spinlock. A process holding the spinlock might easily get scheduled out leading to excessive spinning by everybody. I think a simple thing to try would be to replace the spinlock with LWLock. Yes. Attached is the POC patch that replaces per-counter spinlock with LWLock. > > I did a prototype patch that replaces spinlocks with futexes, but was not able to find a workload where it mattered. I'm not familiar with futex, but could you tell me why you used futex instead of LWLock that we already have? Is futex portable? > We have done a great job at eliminating spinlocks from contended code paths. Robins, perhaps you could try it to see if it reduces the regression you are observing. Yes. Also we need to check that this change doesn't increase performance overhead in other workloads. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Ants Aasma <ants@cybertec.at> — 2020-06-30T11:30:03Z
On Tue, 30 Jun 2020 at 08:43, Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > The problem looks to be that spinlocks are terrible with overloaded > CPU and a contended spinlock. A process holding the spinlock might easily > get scheduled out leading to excessive spinning by everybody. I think a > simple thing to try would be to replace the spinlock with LWLock. > > Yes. Attached is the POC patch that replaces per-counter spinlock with > LWLock. > Great. I think this is the one that should get considered for testing. > > I did a prototype patch that replaces spinlocks with futexes, but was > not able to find a workload where it mattered. > > I'm not familiar with futex, but could you tell me why you used futex > instead > of LWLock that we already have? Is futex portable? > Futex is a Linux kernel call that allows to build a lock that has uncontended cases work fully in user space almost exactly like a spinlock, while falling back to syscalls that wait for wakeup in case of contention. It's not portable, but probably something similar could be implemented for other operating systems. I did not pursue this further because it became apparent that every performance critical spinlock had already been removed. To be clear, I am not advocating for this patch to get included. I just had the patch immediately available and it could have confirmed that using a better lock fixes things. -- Ants Aasma Senior Database Engineerwww.cybertec-postgresql.com
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-06-30T13:40:09Z
On 2020/06/30 20:30, Ants Aasma wrote: > On Tue, 30 Jun 2020 at 08:43, Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> wrote: > > > The problem looks to be that spinlocks are terrible with overloaded CPU and a contended spinlock. A process holding the spinlock might easily get scheduled out leading to excessive spinning by everybody. I think a simple thing to try would be to replace the spinlock with LWLock. > > Yes. Attached is the POC patch that replaces per-counter spinlock with LWLock. > > > Great. I think this is the one that should get considered for testing. > > > I did a prototype patch that replaces spinlocks with futexes, but was not able to find a workload where it mattered. > > I'm not familiar with futex, but could you tell me why you used futex instead > of LWLock that we already have? Is futex portable? > > > Futex is a Linux kernel call that allows to build a lock that has uncontended cases work fully in user space almost exactly like a spinlock, while falling back to syscalls that wait for wakeup in case of contention. It's not portable, but probably something similar could be implemented for other operating systems. I did not pursue this further because it became apparent that every performance critical spinlock had already been removed. > > To be clear, I am not advocating for this patch to get included. I just had the patch immediately available and it could have confirmed that using a better lock fixes things. Understood. Thanks for the explanation! Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-06-30T13:40:40Z
On 2020/06/30 7:29, Peter Geoghegan wrote: > On Mon, Jun 29, 2020 at 3:23 PM Peter Geoghegan <pg@bowt.ie> wrote: >> +1 -- this regression seems unacceptable to me. > > I added an open item to track this. Thanks! I'm thinking to change the default value of track_planning to off for v13. Ants and Andres suggested to replace the spinlock used in pgss_store() with LWLock. I agreed with them and posted the POC patch doing that. But I think the patch is an item for v14. The patch may address the reported performance issue, but may cause other performance issues in other workloads. We would need to measure how the patch affects the performance in various workloads. It seems too late to do that at this stage of v13. Thought? Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Andres Freund <andres@anarazel.de> — 2020-06-30T19:03:20Z
Hi, On 2020-06-30 14:43:39 +0900, Fujii Masao wrote: > > I did a prototype patch that replaces spinlocks with futexes, but was not able to find a workload where it mattered. > > I'm not familiar with futex, but could you tell me why you used futex instead > of LWLock that we already have? Is futex portable? We can't rely on futexes, they're linux only. I also don't see much of a reason to use spinlocks (rather than lwlocks) here in the first place. > diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c > index cef8bb5a49..aa506f6c11 100644 > --- a/contrib/pg_stat_statements/pg_stat_statements.c > +++ b/contrib/pg_stat_statements/pg_stat_statements.c > @@ -39,7 +39,7 @@ > * in an entry except the counters requires the same. To look up an entry, > * one must hold the lock shared. To read or update the counters within > * an entry, one must hold the lock shared or exclusive (so the entry doesn't > - * disappear!) and also take the entry's mutex spinlock. > + * disappear!) and also take the entry's partition lock. > * The shared state variable pgss->extent (the next free spot in the external > * query-text file) should be accessed only while holding either the > * pgss->mutex spinlock, or exclusive lock on pgss->lock. We use the mutex to > @@ -115,6 +115,11 @@ static const uint32 PGSS_PG_MAJOR_VERSION = PG_VERSION_NUM / 100; > > #define JUMBLE_SIZE 1024 /* query serialization buffer size */ > > +#define PGSS_NUM_LOCK_PARTITIONS() (pgss_max) > +#define PGSS_HASH_PARTITION_LOCK(key) \ > + (&(pgss->base + \ > + (get_hash_value(pgss_hash, key) % PGSS_NUM_LOCK_PARTITIONS()))->lock) > + > /* > * Extension version number, for supporting older extension versions' objects > */ > @@ -207,7 +212,7 @@ typedef struct pgssEntry > Size query_offset; /* query text offset in external file */ > int query_len; /* # of valid bytes in query string, or -1 */ > int encoding; /* query text encoding */ > - slock_t mutex; /* protects the counters only */ > + LWLock *lock; /* protects the counters only */ > } pgssEntry; Why did you add the hashing here? It seems a lot better to just add an lwlock in-place instead of the spinlock? The added size is neglegible compared to the size of pgssEntry. Greetings, Andres Freund
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Re: track_planning causing performance regression
Andres Freund <andres@anarazel.de> — 2020-06-30T19:06:13Z
Hi, On 2020-06-30 14:30:03 +0300, Ants Aasma wrote: > Futex is a Linux kernel call that allows to build a lock that has > uncontended cases work fully in user space almost exactly like a spinlock, > while falling back to syscalls that wait for wakeup in case of contention. > It's not portable, but probably something similar could be implemented for > other operating systems. I did not pursue this further because it became > apparent that every performance critical spinlock had already been removed. Our lwlock implementation does have that property already, though. While the kernel wait is implemented using semaphores, those are implemented using futexes internally (posix ones, not sysv ones, so only after whatever version we switched the default to posix semas on linux). I'd rather move towards removing spinlocks from postgres than making their implementation more complicated... Greetings, Andres Freund
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Re: track_planning causing performance regression
Peter Geoghegan <pg@bowt.ie> — 2020-06-30T22:37:05Z
On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > Ants and Andres suggested to replace the spinlock used in pgss_store() with > LWLock. I agreed with them and posted the POC patch doing that. But I think > the patch is an item for v14. The patch may address the reported performance > issue, but may cause other performance issues in other workloads. We would > need to measure how the patch affects the performance in various workloads. > It seems too late to do that at this stage of v13. Thought? I agree that it's too late for v13. Thanks -- Peter Geoghegan
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-07-01T13:20:50Z
On 2020/07/01 4:03, Andres Freund wrote: > Hi, > > On 2020-06-30 14:43:39 +0900, Fujii Masao wrote: >>> I did a prototype patch that replaces spinlocks with futexes, but was not able to find a workload where it mattered. >> >> I'm not familiar with futex, but could you tell me why you used futex instead >> of LWLock that we already have? Is futex portable? > > We can't rely on futexes, they're linux only. Understood. Thanks! > I also don't see much of a > reason to use spinlocks (rather than lwlocks) here in the first place. > > >> diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c >> index cef8bb5a49..aa506f6c11 100644 >> --- a/contrib/pg_stat_statements/pg_stat_statements.c >> +++ b/contrib/pg_stat_statements/pg_stat_statements.c >> @@ -39,7 +39,7 @@ >> * in an entry except the counters requires the same. To look up an entry, >> * one must hold the lock shared. To read or update the counters within >> * an entry, one must hold the lock shared or exclusive (so the entry doesn't >> - * disappear!) and also take the entry's mutex spinlock. >> + * disappear!) and also take the entry's partition lock. >> * The shared state variable pgss->extent (the next free spot in the external >> * query-text file) should be accessed only while holding either the >> * pgss->mutex spinlock, or exclusive lock on pgss->lock. We use the mutex to >> @@ -115,6 +115,11 @@ static const uint32 PGSS_PG_MAJOR_VERSION = PG_VERSION_NUM / 100; >> >> #define JUMBLE_SIZE 1024 /* query serialization buffer size */ >> >> +#define PGSS_NUM_LOCK_PARTITIONS() (pgss_max) >> +#define PGSS_HASH_PARTITION_LOCK(key) \ >> + (&(pgss->base + \ >> + (get_hash_value(pgss_hash, key) % PGSS_NUM_LOCK_PARTITIONS()))->lock) >> + >> /* >> * Extension version number, for supporting older extension versions' objects >> */ >> @@ -207,7 +212,7 @@ typedef struct pgssEntry >> Size query_offset; /* query text offset in external file */ >> int query_len; /* # of valid bytes in query string, or -1 */ >> int encoding; /* query text encoding */ >> - slock_t mutex; /* protects the counters only */ >> + LWLock *lock; /* protects the counters only */ >> } pgssEntry; > > Why did you add the hashing here? It seems a lot better to just add an > lwlock in-place instead of the spinlock? The added size is neglegible > compared to the size of pgssEntry. Because pgssEntry is not array entry but hashtable entry. First I was thinking to assign per-process lwlock to each entry in the array at the startup. But each entry is created every time new entry is required. So lwlock needs to be assigned to each entry at that creation time. We cannnot easily assign lwlock to all the entries at the startup. Also each entry can be dropped from the hashtable. In this case, maybe already-assigned lwlock needs to be moved back to "freelist" so that it will be able to be assigned again to new entry later. We can implement this probably, but which looks a bit complicated. Since the hasing addresses these issues, I just used it in POC patch. But I'd like to hear better idea! > +#define PGSS_NUM_LOCK_PARTITIONS() (pgss_max) Currently pgss_max is used as the number of lwlock for entries. But if too large number of lwlock is useless (or a bit harmful?), we can set the upper limit here, e.g., max(pgss_max, 10000). Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Andres Freund <andres@anarazel.de> — 2020-07-01T16:54:25Z
Hi, On 2020-07-01 22:20:50 +0900, Fujii Masao wrote: > On 2020/07/01 4:03, Andres Freund wrote: > > Why did you add the hashing here? It seems a lot better to just add an > > lwlock in-place instead of the spinlock? The added size is neglegible > > compared to the size of pgssEntry. > > Because pgssEntry is not array entry but hashtable entry. First I was > thinking to assign per-process lwlock to each entry in the array at the > startup. But each entry is created every time new entry is required. > So lwlock needs to be assigned to each entry at that creation time. > We cannnot easily assign lwlock to all the entries at the startup. But why not just do it exactly at the place the SpinLockInit() is done currently? Greetings, Andres Freund
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-07-03T01:56:51Z
On 2020/07/02 1:54, Andres Freund wrote: > Hi, > > On 2020-07-01 22:20:50 +0900, Fujii Masao wrote: >> On 2020/07/01 4:03, Andres Freund wrote: >>> Why did you add the hashing here? It seems a lot better to just add an >>> lwlock in-place instead of the spinlock? The added size is neglegible >>> compared to the size of pgssEntry. >> >> Because pgssEntry is not array entry but hashtable entry. First I was >> thinking to assign per-process lwlock to each entry in the array at the >> startup. But each entry is created every time new entry is required. >> So lwlock needs to be assigned to each entry at that creation time. >> We cannnot easily assign lwlock to all the entries at the startup. > > But why not just do it exactly at the place the SpinLockInit() is done > currently? Sorry I failed to understand your point... You mean that new lwlock should be initialized at the place the SpinLockInit() is done currently instead of requesting postmaster to initialize all the lwlocks required for pgss at _PG_init()? Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-07-03T02:39:34Z
On 2020/07/01 7:37, Peter Geoghegan wrote: > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: >> Ants and Andres suggested to replace the spinlock used in pgss_store() with >> LWLock. I agreed with them and posted the POC patch doing that. But I think >> the patch is an item for v14. The patch may address the reported performance >> issue, but may cause other performance issues in other workloads. We would >> need to measure how the patch affects the performance in various workloads. >> It seems too late to do that at this stage of v13. Thought? > > I agree that it's too late for v13. Thanks for the comment! So I pushed the patch and changed default of track_planning to off. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Peter Geoghegan <pg@bowt.ie> — 2020-07-03T02:43:46Z
On Thu, Jul 2, 2020 at 7:39 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > So I pushed the patch and changed default of track_planning to off. I have closed out the open item I created for this. Thanks! -- Peter Geoghegan
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-07-03T02:48:58Z
On 2020/07/03 11:43, Peter Geoghegan wrote: > On Thu, Jul 2, 2020 at 7:39 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: >> So I pushed the patch and changed default of track_planning to off. > > I have closed out the open item I created for this. Thanks!! I added the patch that replaces spinlock with lwlock in pgss, into CF-2020-09. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Pavel Stehule <pavel.stehule@gmail.com> — 2020-07-03T04:05:10Z
Hi pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com> napsal: > > > On 2020/07/01 7:37, Peter Geoghegan wrote: > > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao <masao.fujii@oss.nttdata.com> > wrote: > >> Ants and Andres suggested to replace the spinlock used in pgss_store() > with > >> LWLock. I agreed with them and posted the POC patch doing that. But I > think > >> the patch is an item for v14. The patch may address the reported > performance > >> issue, but may cause other performance issues in other workloads. We > would > >> need to measure how the patch affects the performance in various > workloads. > >> It seems too late to do that at this stage of v13. Thought? > > > > I agree that it's too late for v13. > > Thanks for the comment! > > So I pushed the patch and changed default of track_planning to off. > Maybe there can be documented so enabling this option can have a negative impact on performance. Regards Pavel > > Regards, > > -- > Fujii Masao > Advanced Computing Technology Center > Research and Development Headquarters > NTT DATA CORPORATION > > >
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-07-03T06:57:38Z
On 2020/07/03 13:05, Pavel Stehule wrote: > Hi > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> napsal: > > > > On 2020/07/01 7:37, Peter Geoghegan wrote: > > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> wrote: > >> Ants and Andres suggested to replace the spinlock used in pgss_store() with > >> LWLock. I agreed with them and posted the POC patch doing that. But I think > >> the patch is an item for v14. The patch may address the reported performance > >> issue, but may cause other performance issues in other workloads. We would > >> need to measure how the patch affects the performance in various workloads. > >> It seems too late to do that at this stage of v13. Thought? > > > > I agree that it's too late for v13. > > Thanks for the comment! > > So I pushed the patch and changed default of track_planning to off. > > > Maybe there can be documented so enabling this option can have a negative impact on performance. Yes. What about adding either of the followings into the doc? Enabling this parameter may incur a noticeable performance penalty. or Enabling this parameter may incur a noticeable performance penalty, especially when a fewer kinds of queries are executed on many concurrent connections. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION -
Re: track_planning causing performance regression
Pavel Stehule <pavel.stehule@gmail.com> — 2020-07-03T07:02:10Z
pá 3. 7. 2020 v 8:57 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com> napsal: > > > On 2020/07/03 13:05, Pavel Stehule wrote: > > Hi > > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com > <mailto:masao.fujii@oss.nttdata.com>> napsal: > > > > > > > > On 2020/07/01 7:37, Peter Geoghegan wrote: > > > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> wrote: > > >> Ants and Andres suggested to replace the spinlock used in > pgss_store() with > > >> LWLock. I agreed with them and posted the POC patch doing that. > But I think > > >> the patch is an item for v14. The patch may address the reported > performance > > >> issue, but may cause other performance issues in other > workloads. We would > > >> need to measure how the patch affects the performance in various > workloads. > > >> It seems too late to do that at this stage of v13. Thought? > > > > > > I agree that it's too late for v13. > > > > Thanks for the comment! > > > > So I pushed the patch and changed default of track_planning to off. > > > > > > Maybe there can be documented so enabling this option can have a > negative impact on performance. > > Yes. What about adding either of the followings into the doc? > > Enabling this parameter may incur a noticeable performance penalty. > > or > > Enabling this parameter may incur a noticeable performance penalty, > especially when a fewer kinds of queries are executed on many > concurrent connections. > This second variant looks perfect for this case. Thank you Pavel > Regards, > > -- > Fujii Masao > Advanced Computing Technology Center > Research and Development Headquarters > NTT DATA CORPORATION >
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-07-03T11:02:03Z
On 2020/07/03 16:02, Pavel Stehule wrote: > > > pá 3. 7. 2020 v 8:57 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> napsal: > > > > On 2020/07/03 13:05, Pavel Stehule wrote: > > Hi > > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> napsal: > > > > > > > > On 2020/07/01 7:37, Peter Geoghegan wrote: > > > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> wrote: > > >> Ants and Andres suggested to replace the spinlock used in pgss_store() with > > >> LWLock. I agreed with them and posted the POC patch doing that. But I think > > >> the patch is an item for v14. The patch may address the reported performance > > >> issue, but may cause other performance issues in other workloads. We would > > >> need to measure how the patch affects the performance in various workloads. > > >> It seems too late to do that at this stage of v13. Thought? > > > > > > I agree that it's too late for v13. > > > > Thanks for the comment! > > > > So I pushed the patch and changed default of track_planning to off. > > > > > > Maybe there can be documented so enabling this option can have a negative impact on performance. > > Yes. What about adding either of the followings into the doc? > > Enabling this parameter may incur a noticeable performance penalty. > > or > > Enabling this parameter may incur a noticeable performance penalty, > especially when a fewer kinds of queries are executed on many > concurrent connections. > > > This second variant looks perfect for this case. Ok, so patch attached. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Pavel Stehule <pavel.stehule@gmail.com> — 2020-07-04T03:22:31Z
pá 3. 7. 2020 v 13:02 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com> napsal: > > > On 2020/07/03 16:02, Pavel Stehule wrote: > > > > > > pá 3. 7. 2020 v 8:57 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com > <mailto:masao.fujii@oss.nttdata.com>> napsal: > > > > > > > > On 2020/07/03 13:05, Pavel Stehule wrote: > > > Hi > > > > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> napsal: > > > > > > > > > > > > On 2020/07/01 7:37, Peter Geoghegan wrote: > > > > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> wrote: > > > >> Ants and Andres suggested to replace the spinlock used in > pgss_store() with > > > >> LWLock. I agreed with them and posted the POC patch doing > that. But I think > > > >> the patch is an item for v14. The patch may address the > reported performance > > > >> issue, but may cause other performance issues in other > workloads. We would > > > >> need to measure how the patch affects the performance in > various workloads. > > > >> It seems too late to do that at this stage of v13. > Thought? > > > > > > > > I agree that it's too late for v13. > > > > > > Thanks for the comment! > > > > > > So I pushed the patch and changed default of track_planning > to off. > > > > > > > > > Maybe there can be documented so enabling this option can have a > negative impact on performance. > > > > Yes. What about adding either of the followings into the doc? > > > > Enabling this parameter may incur a noticeable performance > penalty. > > > > or > > > > Enabling this parameter may incur a noticeable performance > penalty, > > especially when a fewer kinds of queries are executed on many > > concurrent connections. > > > > > > This second variant looks perfect for this case. > > Ok, so patch attached. > +1 Thank you Pavel > Regards, > > -- > Fujii Masao > Advanced Computing Technology Center > Research and Development Headquarters > NTT DATA CORPORATION >
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-07-06T05:29:28Z
On 2020/07/04 12:22, Pavel Stehule wrote: > > > pá 3. 7. 2020 v 13:02 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> napsal: > > > > On 2020/07/03 16:02, Pavel Stehule wrote: > > > > > > pá 3. 7. 2020 v 8:57 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> napsal: > > > > > > > > On 2020/07/03 13:05, Pavel Stehule wrote: > > > Hi > > > > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>> napsal: > > > > > > > > > > > > On 2020/07/01 7:37, Peter Geoghegan wrote: > > > > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>> wrote: > > > >> Ants and Andres suggested to replace the spinlock used in pgss_store() with > > > >> LWLock. I agreed with them and posted the POC patch doing that. But I think > > > >> the patch is an item for v14. The patch may address the reported performance > > > >> issue, but may cause other performance issues in other workloads. We would > > > >> need to measure how the patch affects the performance in various workloads. > > > >> It seems too late to do that at this stage of v13. Thought? > > > > > > > > I agree that it's too late for v13. > > > > > > Thanks for the comment! > > > > > > So I pushed the patch and changed default of track_planning to off. > > > > > > > > > Maybe there can be documented so enabling this option can have a negative impact on performance. > > > > Yes. What about adding either of the followings into the doc? > > > > Enabling this parameter may incur a noticeable performance penalty. > > > > or > > > > Enabling this parameter may incur a noticeable performance penalty, > > especially when a fewer kinds of queries are executed on many > > concurrent connections. > > > > > > This second variant looks perfect for this case. > > Ok, so patch attached. > > > +1 Thanks for the review! Pushed. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Hamid Akhtar <hamid.akhtar@gmail.com> — 2020-07-31T12:40:34Z
<https://commitfest.postgresql.org/29/2634/> On Mon, Jul 6, 2020 at 10:29 AM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > > On 2020/07/04 12:22, Pavel Stehule wrote: > > > > > > pá 3. 7. 2020 v 13:02 odesílatel Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> napsal: > > > > > > > > On 2020/07/03 16:02, Pavel Stehule wrote: > > > > > > > > > pá 3. 7. 2020 v 8:57 odesílatel Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> napsal: > > > > > > > > > > > > On 2020/07/03 13:05, Pavel Stehule wrote: > > > > Hi > > > > > > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>> > napsal: > > > > > > > > > > > > > > > > On 2020/07/01 7:37, Peter Geoghegan wrote: > > > > > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>> wrote: > > > > >> Ants and Andres suggested to replace the spinlock > used in pgss_store() with > > > > >> LWLock. I agreed with them and posted the POC > patch doing that. But I think > > > > >> the patch is an item for v14. The patch may > address the reported performance > > > > >> issue, but may cause other performance issues in > other workloads. We would > > > > >> need to measure how the patch affects the > performance in various workloads. > > > > >> It seems too late to do that at this stage of v13. > Thought? > > > > > > > > > > I agree that it's too late for v13. > > > > > > > > Thanks for the comment! > > > > > > > > So I pushed the patch and changed default of > track_planning to off. > > > > > > > > > > > > Maybe there can be documented so enabling this option can > have a negative impact on performance. > > > > > > Yes. What about adding either of the followings into the doc? > > > > > > Enabling this parameter may incur a noticeable > performance penalty. > > > > > > or > > > > > > Enabling this parameter may incur a noticeable > performance penalty, > > > especially when a fewer kinds of queries are executed > on many > > > concurrent connections. > > > > > > > > > This second variant looks perfect for this case. > > > > Ok, so patch attached. > > > > > > +1 > > Thanks for the review! Pushed. > > Regards, > > -- > Fujii Masao > Advanced Computing Technology Center > Research and Development Headquarters > NTT DATA CORPORATION > > > You might also want to update this patch's status in the commitfest: https://commitfest.postgresql.org/29/2634/ -- Highgo Software (Canada/China/Pakistan) URL : www.highgo.ca ADDR: 10318 WHALLEY BLVD, Surrey, BC CELL：+923335449950 EMAIL: mailto:hamid.akhtar@highgo.ca SKYPE: engineeredvirus
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-08-17T09:21:41Z
On 2020/07/31 21:40, Hamid Akhtar wrote: > <https://commitfest.postgresql.org/29/2634/> > > On Mon, Jul 6, 2020 at 10:29 AM Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> wrote: > > > > On 2020/07/04 12:22, Pavel Stehule wrote: > > > > > > pá 3. 7. 2020 v 13:02 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> napsal: > > > > > > > > On 2020/07/03 16:02, Pavel Stehule wrote: > > > > > > > > > pá 3. 7. 2020 v 8:57 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>> napsal: > > > > > > > > > > > > On 2020/07/03 13:05, Pavel Stehule wrote: > > > > Hi > > > > > > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>>> napsal: > > > > > > > > > > > > > > > > On 2020/07/01 7:37, Peter Geoghegan wrote: > > > > > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>>> wrote: > > > > >> Ants and Andres suggested to replace the spinlock used in pgss_store() with > > > > >> LWLock. I agreed with them and posted the POC patch doing that. But I think > > > > >> the patch is an item for v14. The patch may address the reported performance > > > > >> issue, but may cause other performance issues in other workloads. We would > > > > >> need to measure how the patch affects the performance in various workloads. > > > > >> It seems too late to do that at this stage of v13. Thought? > > > > > > > > > > I agree that it's too late for v13. > > > > > > > > Thanks for the comment! > > > > > > > > So I pushed the patch and changed default of track_planning to off. > > > > > > > > > > > > Maybe there can be documented so enabling this option can have a negative impact on performance. > > > > > > Yes. What about adding either of the followings into the doc? > > > > > > Enabling this parameter may incur a noticeable performance penalty. > > > > > > or > > > > > > Enabling this parameter may incur a noticeable performance penalty, > > > especially when a fewer kinds of queries are executed on many > > > concurrent connections. > > > > > > > > > This second variant looks perfect for this case. > > > > Ok, so patch attached. > > > > > > +1 > > Thanks for the review! Pushed. > > Regards, > > -- > Fujii Masao > Advanced Computing Technology Center > Research and Development Headquarters > NTT DATA CORPORATION > > > > You might also want to update this patch's status in the commitfest: > https://commitfest.postgresql.org/29/2634/ The patch added into this CF entry has not been committed yet. So I was thinking that there is no need to update the status yet. No? Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Hamid Akhtar <hamid.akhtar@gmail.com> — 2020-08-17T09:34:18Z
On Mon, Aug 17, 2020 at 2:21 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > > On 2020/07/31 21:40, Hamid Akhtar wrote: > > <https://commitfest.postgresql.org/29/2634/> > > > > On Mon, Jul 6, 2020 at 10:29 AM Fujii Masao <masao.fujii@oss.nttdata.com > <mailto:masao.fujii@oss.nttdata.com>> wrote: > > > > > > > > On 2020/07/04 12:22, Pavel Stehule wrote: > > > > > > > > > pá 3. 7. 2020 v 13:02 odesílatel Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> napsal: > > > > > > > > > > > > On 2020/07/03 16:02, Pavel Stehule wrote: > > > > > > > > > > > > pá 3. 7. 2020 v 8:57 odesílatel Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>> > napsal: > > > > > > > > > > > > > > > > On 2020/07/03 13:05, Pavel Stehule wrote: > > > > > Hi > > > > > > > > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> > <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> > <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> > <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> > <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>>> > napsal: > > > > > > > > > > > > > > > > > > > > On 2020/07/01 7:37, Peter Geoghegan wrote: > > > > > > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao < > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto: > masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> > <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> > <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> > <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> > <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>>> > wrote: > > > > > >> Ants and Andres suggested to replace the > spinlock used in pgss_store() with > > > > > >> LWLock. I agreed with them and posted the > POC patch doing that. But I think > > > > > >> the patch is an item for v14. The patch may > address the reported performance > > > > > >> issue, but may cause other performance > issues in other workloads. We would > > > > > >> need to measure how the patch affects the > performance in various workloads. > > > > > >> It seems too late to do that at this stage > of v13. Thought? > > > > > > > > > > > > I agree that it's too late for v13. > > > > > > > > > > Thanks for the comment! > > > > > > > > > > So I pushed the patch and changed default of > track_planning to off. > > > > > > > > > > > > > > > Maybe there can be documented so enabling this > option can have a negative impact on performance. > > > > > > > > Yes. What about adding either of the followings into > the doc? > > > > > > > > Enabling this parameter may incur a noticeable > performance penalty. > > > > > > > > or > > > > > > > > Enabling this parameter may incur a noticeable > performance penalty, > > > > especially when a fewer kinds of queries are > executed on many > > > > concurrent connections. > > > > > > > > > > > > This second variant looks perfect for this case. > > > > > > Ok, so patch attached. > > > > > > > > > +1 > > > > Thanks for the review! Pushed. > > > > Regards, > > > > -- > > Fujii Masao > > Advanced Computing Technology Center > > Research and Development Headquarters > > NTT DATA CORPORATION > > > > > > > > You might also want to update this patch's status in the commitfest: > > https://commitfest.postgresql.org/29/2634/ > > The patch added into this CF entry has not been committed yet. > So I was thinking that there is no need to update the status yet. No? > Your previous email suggested that it's been pushed, hence my comment. Checking the git log, I see a commit was pushed on July 6 (321fa6a) with the changes that match the latest patch. Am I missing something here? > > Regards, > > -- > Fujii Masao > Advanced Computing Technology Center > Research and Development Headquarters > NTT DATA CORPORATION > -- Highgo Software (Canada/China/Pakistan) URL : www.highgo.ca ADDR: 10318 WHALLEY BLVD, Surrey, BC CELL：+923335449950 EMAIL: mailto:hamid.akhtar@highgo.ca SKYPE: engineeredvirus
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-08-17T12:30:31Z
On 2020/08/17 18:34, Hamid Akhtar wrote: > > > On Mon, Aug 17, 2020 at 2:21 PM Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> wrote: > > > > On 2020/07/31 21:40, Hamid Akhtar wrote: > > <https://commitfest.postgresql.org/29/2634/> > > > > On Mon, Jul 6, 2020 at 10:29 AM Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> wrote: > > > > > > > > On 2020/07/04 12:22, Pavel Stehule wrote: > > > > > > > > > pá 3. 7. 2020 v 13:02 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>> napsal: > > > > > > > > > > > > On 2020/07/03 16:02, Pavel Stehule wrote: > > > > > > > > > > > > pá 3. 7. 2020 v 8:57 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>>> napsal: > > > > > > > > > > > > > > > > On 2020/07/03 13:05, Pavel Stehule wrote: > > > > > Hi > > > > > > > > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> <mailto:masao.fujii@oss.nttdata.com > <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>>>> napsal: > > > > > > > > > > > > > > > > > > > > On 2020/07/01 7:37, Peter Geoghegan wrote: > > > > > > On Tue, Jun 30, 2020 at 6:40 AM Fujii Masao <masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>> > <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com> <mailto:masao.fujii@oss.nttdata.com <mailto:masao.fujii@oss.nttdata.com>>>>>> wrote: > > > > > >> Ants and Andres suggested to replace the spinlock used in pgss_store() with > > > > > >> LWLock. I agreed with them and posted the POC patch doing that. But I think > > > > > >> the patch is an item for v14. The patch may address the reported performance > > > > > >> issue, but may cause other performance issues in other workloads. We would > > > > > >> need to measure how the patch affects the performance in various workloads. > > > > > >> It seems too late to do that at this stage of v13. Thought? > > > > > > > > > > > > I agree that it's too late for v13. > > > > > > > > > > Thanks for the comment! > > > > > > > > > > So I pushed the patch and changed default of track_planning to off. > > > > > > > > > > > > > > > Maybe there can be documented so enabling this option can have a negative impact on performance. > > > > > > > > Yes. What about adding either of the followings into the doc? > > > > > > > > Enabling this parameter may incur a noticeable performance penalty. > > > > > > > > or > > > > > > > > Enabling this parameter may incur a noticeable performance penalty, > > > > especially when a fewer kinds of queries are executed on many > > > > concurrent connections. > > > > > > > > > > > > This second variant looks perfect for this case. > > > > > > Ok, so patch attached. > > > > > > > > > +1 > > > > Thanks for the review! Pushed. > > > > Regards, > > > > -- > > Fujii Masao > > Advanced Computing Technology Center > > Research and Development Headquarters > > NTT DATA CORPORATION > > > > > > > > You might also want to update this patch's status in the commitfest: > > https://commitfest.postgresql.org/29/2634/ > > The patch added into this CF entry has not been committed yet. > So I was thinking that there is no need to update the status yet. No? > > > Your previous email suggested that it's been pushed, hence my comment. Checking the git log, I see a commit was pushed on July 6 (321fa6a) with the changes that match the latest patch. Yes, I pushed the document_overhead_by_track_planning.patch, but this CF entry is for pgss_lwlock_v1.patch which replaces spinlocks with lwlocks in pg_stat_statements. The latter patch has not been committed yet. Probably attachding the different patches in the same thread would cause this confusing thing... Anyway, thanks for your comment! Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-08-18T15:43:49Z
> Yes, I pushed the document_overhead_by_track_planning.patch, but this > CF entry is for pgss_lwlock_v1.patch which replaces spinlocks with lwlocks > in pg_stat_statements. The latter patch has not been committed yet. > Probably attachding the different patches in the same thread would cause > this confusing thing... Anyway, thanks for your comment! To avoid further confusion, I attached the rebased version of the patch that was registered at CF. I'd appreciate it if you review this version. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Hamid Akhtar <hamid.akhtar@gmail.com> — 2020-08-18T15:44:48Z
On Tue, Aug 18, 2020 at 8:43 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > > Yes, I pushed the document_overhead_by_track_planning.patch, but this > > CF entry is for pgss_lwlock_v1.patch which replaces spinlocks with > lwlocks > > in pg_stat_statements. The latter patch has not been committed yet. > > Probably attachding the different patches in the same thread would cause > > this confusing thing... Anyway, thanks for your comment! > > To avoid further confusion, I attached the rebased version of > the patch that was registered at CF. I'd appreciate it if > you review this version. > Thank you. Reviewing it now. > > Regards, > > -- > Fujii Masao > Advanced Computing Technology Center > Research and Development Headquarters > NTT DATA CORPORATION > -- Highgo Software (Canada/China/Pakistan) URL : www.highgo.ca ADDR: 10318 WHALLEY BLVD, Surrey, BC CELL：+923335449950 EMAIL: mailto:hamid.akhtar@highgo.ca SKYPE: engineeredvirus
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Re: track_planning causing performance regression
Hamid Akhtar <hamid.akhtar@gmail.com> — 2020-08-19T12:45:41Z
The following review has been posted through the commitfest application: make installcheck-world: tested, passed Implements feature: not tested Spec compliant: not tested Documentation: not tested Overall, the patch works fine. However, I have a few observations: (1) Code Comments: - The code comments should be added for the 2 new macros, in particular for PGSS_NUM_LOCK_PARTITIONS. As you explained in your email, this may be used to limit the number of locks if a very large value for pgss_max is specified. - From the code I inferred that the number of locks can in future be less than pgss_max (per your email where in future this macro could be used to limit the number of locks). I suggest to perhaps add some notes helping future changes in this code area. (2) It seems like that "pgss->lock = &(pgss->base + pgss_max)->lock;" statement should not use pgss_max directly and instead use PGSS_NUM_LOCK_PARTITIONS macro, as when a limit is imposed on number of locks, this statement will cause an overrun. -- Highgo Software (Canada/China/Pakistan) URL : www.highgo.ca ADDR: 10318 WHALLEY BLVD, Surrey, BC CELL：+923335449950 EMAIL: mailto:hamid.akhtar@highgo.ca SKYPE: engineeredvirus The new status of this patch is: Waiting on Author
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Re: track_planning causing performance regression
bttanakahbk <bttanakahbk@oss.nttdata.com> — 2020-09-11T07:23:28Z
Hi, On 2020-08-19 00:43, Fujii Masao wrote: >> Yes, I pushed the document_overhead_by_track_planning.patch, but this >> CF entry is for pgss_lwlock_v1.patch which replaces spinlocks with >> lwlocks >> in pg_stat_statements. The latter patch has not been committed yet. >> Probably attachding the different patches in the same thread would >> cause >> this confusing thing... Anyway, thanks for your comment! > > To avoid further confusion, I attached the rebased version of > the patch that was registered at CF. I'd appreciate it if > you review this version. I tested pgss_lwlock_v2.patch with 3 workloads. And I couldn't observe performance improvement in our environment and I'm afraid to say that even worser in some case. - Workload1: pgbench select-only mode - Workload2: pgbench custom scripts which run "SELECT 1;" - Workload3: pgbench custom scripts which run 1000 types of different simple queries - Workload1 First we set the pg_stat_statements.track_planning to on/off and run the fully-cached pgbench select-only mode on pg14head which is installed in on-premises server(32CPU, 256GB mem). However in this enveronment we couldn't reproduce 45% performance drop due to s_lock conflict (Tharakan-san mentioned in his post on 2895b53b033c47ccb22972b589050dd9@EX13D05UWC001.ant.amazon.com). - Workload2 Then we adopted pgbench custom script "SELECT 1;" which supposed to increase the s_lock and make it easier to reproduce the issue. In this case around 10% of performance decrease which also shows slightly increase in s_lock (~10%). With this senario, despite a s_lock absence, the patch shows more than 50% performance degradation regardless of track_planning. And also we couldn't see performance improvement in this workload. pgbench: initialization: pgbench -i -s 100 benchmarking : pgbench -j16 -c128 -T180 -r -n -f <script> -h <address> -U <user> -p <port> -d <db> # VACUUMed and pg_prewarmed manually before run the benchmark query：SELECT 1; > pgss_lwlock_v2.patch track_planning TPS decline rate > s_lock CPU usage > - OFF 810509.4 standard > 0.17% 98.8％（sys24.9%,user73.9%） > - ON 732823.1 -9.6% > 1.94% 95.1％（sys22.8%,user72.3%） > + OFF 371035.0 -49.4% - > 65.2％（sys20.6%,user44.6%） > + ON 193965.2 -47.7% - > 41.8％（sys12.1%,user29.7%） # "-" is showing that s_lock was not reported from the perf. - Workload3 Next, there is concern that replacement of LWLock may reduce performance in some other workloads. (Fujii-san mentioned in his post on 42a13b4c-e60c-c6e7-3475-8eff8050bed4@oss.nttdata.com). To clarify this, we prepared 1000 simple queries which is supposed to prevent the conflict of s_lock and may expect to see the behavior without s_lock. In this case, no performance decline was observed and also we couldn't see any additional memory consumption or cpu usage. pgbench: initialization: pgbench -n -i -s 100 --partitions=1000 --partition-method=range benchmarking : command is same as (Workload1) query: SELECT abalance FROM pgbench_accounts_xxxx WHERE aid = :aid + (10000 * :random_num - 10000); > pgss_lwlock_v2.patch track_planning TPS decline rate CPU > usage > - OFF 88329.1 standard > 82.1%（sys6.5%,user75.6%） > - ON 88015.3 -0.36% > 82.6%（sys6.5%,user76.1%） > + OFF 88177.5 0.18% > 82.2%（sys6.5%,user75.7%） > + ON 88079.1 -0.11% > 82.5%（sys6.5%,user76.0%） (Environment) machine: server/client - 32 CPUs / 256GB # used same machine as server & client postgres: version: v14 (6eee73e) configure: '--prefix=/usr/pgsql-14a' 'CFLAGS=-O2' GUC param (changed from defaults): shared_preload_libraries = 'pg_stat_statements, pg_prewarm' autovacuum = off checkpoint = 120min max_connections=300 listen_address='*' shared_buffers=64GB Regards, -- Hibiki Tanaka
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-09-11T14:04:41Z
On 2020/09/11 16:23, bttanakahbk wrote: > Hi, > > On 2020-08-19 00:43, Fujii Masao wrote: >>> Yes, I pushed the document_overhead_by_track_planning.patch, but this >>> CF entry is for pgss_lwlock_v1.patch which replaces spinlocks with lwlocks >>> in pg_stat_statements. The latter patch has not been committed yet. >>> Probably attachding the different patches in the same thread would cause >>> this confusing thing... Anyway, thanks for your comment! >> >> To avoid further confusion, I attached the rebased version of >> the patch that was registered at CF. I'd appreciate it if >> you review this version. > > I tested pgss_lwlock_v2.patch with 3 workloads. And I couldn't observe performance > improvement in our environment and I'm afraid to say that even worser in some case. > - Workload1: pgbench select-only mode > - Workload2: pgbench custom scripts which run "SELECT 1;" > - Workload3: pgbench custom scripts which run 1000 types of different simple queries Thanks for running the benchmarks! > > - Workload1 > First we set the pg_stat_statements.track_planning to on/off and run the fully-cached pgbench > select-only mode on pg14head which is installed in on-premises server(32CPU, 256GB mem). > However in this enveronment we couldn't reproduce 45% performance drop due to s_lock conflict > (Tharakan-san mentioned in his post on 2895b53b033c47ccb22972b589050dd9@EX13D05UWC001.ant.amazon.com). > > - Workload2 > Then we adopted pgbench custom script "SELECT 1;" which supposed to increase the s_lock and > make it easier to reproduce the issue. In this case around 10% of performance decrease > which also shows slightly increase in s_lock (~10%). With this senario, despite a s_lock > absence, the patch shows more than 50% performance degradation regardless of track_planning. > And also we couldn't see performance improvement in this workload. > > pgbench: > initialization: pgbench -i -s 100 > benchmarking : pgbench -j16 -c128 -T180 -r -n -f <script> -h <address> -U <user> -p <port> -d <db> > # VACUUMed and pg_prewarmed manually before run the benchmark > query：SELECT 1; >> pgss_lwlock_v2.patch track_planning TPS decline rate s_lock CPU usage >> - OFF 810509.4 standard 0.17% 98.8％（sys24.9%,user73.9%） >> - ON 732823.1 -9.6% 1.94% 95.1％（sys22.8%,user72.3%） >> + OFF 371035.0 -49.4% - 65.2％（sys20.6%,user44.6%） >> + ON 193965.2 -47.7% - 41.8％（sys12.1%,user29.7%） > # "-" is showing that s_lock was not reported from the perf. Ok, so my proposed patch degrated the performance in this case :( This means that replacing spinlock with lwlock in pgss is not proper approach for the lock contention issue on pgss... I proposed to split the spinlock for each pgss entry into two to reduce the lock contention, upthread. One is for planner stats, and the other is for executor stats. Is it worth working on this approach as an alternative idea? Or does anyone have any better idea? Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Julien Rouhaud <rjuju123@gmail.com> — 2020-09-11T19:41:48Z
On Fri, Sep 11, 2020 at 4:04 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > On 2020/09/11 16:23, bttanakahbk wrote: > > > > pgbench: > > initialization: pgbench -i -s 100 > > benchmarking : pgbench -j16 -c128 -T180 -r -n -f <script> -h <address> -U <user> -p <port> -d <db> > > # VACUUMed and pg_prewarmed manually before run the benchmark > > query：SELECT 1; > >> pgss_lwlock_v2.patch track_planning TPS decline rate s_lock CPU usage > >> - OFF 810509.4 standard 0.17% 98.8％（sys24.9%,user73.9%） > >> - ON 732823.1 -9.6% 1.94% 95.1％（sys22.8%,user72.3%） > >> + OFF 371035.0 -49.4% - 65.2％（sys20.6%,user44.6%） > >> + ON 193965.2 -47.7% - 41.8％（sys12.1%,user29.7%） > > # "-" is showing that s_lock was not reported from the perf. > > Ok, so my proposed patch degrated the performance in this case :( > This means that replacing spinlock with lwlock in pgss is not proper > approach for the lock contention issue on pgss... > > I proposed to split the spinlock for each pgss entry into two > to reduce the lock contention, upthread. One is for planner stats, > and the other is for executor stats. Is it worth working on > this approach as an alternative idea? Or does anyone have any better idea? For now only calls and [min|max|mean|total]_time are split between planning and execution, so we'd have to do the same for the rest of the counters to be able to have 2 different spinlocks. That'll increase the size of the struct quite a lot, and we'd also have to change the SRF output, which is already quite wide.
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Re: track_planning causing performance regression
Alvaro Herrera <alvherre@2ndquadrant.com> — 2020-09-11T22:10:05Z
On 2020-Sep-11, Fujii Masao wrote: > Ok, so my proposed patch degrated the performance in this case :( > This means that replacing spinlock with lwlock in pgss is not proper > approach for the lock contention issue on pgss... > > I proposed to split the spinlock for each pgss entry into two > to reduce the lock contention, upthread. One is for planner stats, > and the other is for executor stats. Is it worth working on > this approach as an alternative idea? Or does anyone have any better idea? It does seem that the excl-locked section in pgss_store is rather large. (I admit I don't understand why would a LWLock decrease performance.) Andres suggested in [1] to use atomics for the counters together with a single lwlock to be used in shared mode only. I didn't quite understand what the lwlock is *for*, but maybe you do. [1] https://postgr.es/m/20200629231015.qlej5b3qpfe4uijo@alap3.anarazel.de -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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Re: track_planning causing performance regression
Andres Freund <andres@anarazel.de> — 2020-09-11T22:32:54Z
Hi, On 2020-09-11 19:10:05 -0300, Alvaro Herrera wrote: > Andres suggested in [1] to use atomics for the counters together with a > single lwlock to be used in shared mode only. I didn't quite understand > what the lwlock is *for*, but maybe you do. > > [1] https://postgr.es/m/20200629231015.qlej5b3qpfe4uijo@alap3.anarazel.de Just to be clear - I am saying that in the first iteration I would just straight up replace the spinlock with an lwlock, i.e. having many lwlocks. The piece about a single shared lwlocks is/was about protecting the set of entries that are currently in-memory - which can't easily be implemented just using atomics (at least without the risk of increasing the counters of an entry since replaced with another query). Greetings, Andres Freund
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Re: track_planning causing performance regression
Michael Paquier <michael@paquier.xyz> — 2020-09-30T07:11:55Z
On Fri, Sep 11, 2020 at 03:32:54PM -0700, Andres Freund wrote: > The piece about a single shared lwlocks is/was about protecting the set > of entries that are currently in-memory - which can't easily be > implemented just using atomics (at least without the risk of increasing > the counters of an entry since replaced with another query). This discussion has stalled, and the patch proposed is incorrect, so I have marked it as RwF in the CF app. -- Michael
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Re: track_planning causing performance regression
Justin Pryzby <pryzby@telsasoft.com> — 2021-04-18T23:36:15Z
Reviewing this change which was committed last year as 321fa6a4a26c9b649a0fbec9fc8b019f19e62289 On Fri, Jul 03, 2020 at 03:57:38PM +0900, Fujii Masao wrote: > On 2020/07/03 13:05, Pavel Stehule wrote: > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com> napsal: > > > > Maybe there can be documented so enabling this option can have a negative impact on performance. > > Yes. What about adding either of the followings into the doc? > > Enabling this parameter may incur a noticeable performance penalty. > > or > > Enabling this parameter may incur a noticeable performance penalty, > especially when a fewer kinds of queries are executed on many > concurrent connections. Something seems is wrong with this sentence, and I'm not sure what it's trying to say. Is this right ? > Enabling this parameter may incur a noticeable performance penalty, > especially when a small number of queries are executed on many > concurrent connections. -- Justin
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2021-04-19T14:44:05Z
On 2021/04/19 8:36, Justin Pryzby wrote: > Reviewing this change which was committed last year as > 321fa6a4a26c9b649a0fbec9fc8b019f19e62289 > > On Fri, Jul 03, 2020 at 03:57:38PM +0900, Fujii Masao wrote: >> On 2020/07/03 13:05, Pavel Stehule wrote: >>> pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com> napsal: >>> >>> Maybe there can be documented so enabling this option can have a negative impact on performance. >> >> Yes. What about adding either of the followings into the doc? >> >> Enabling this parameter may incur a noticeable performance penalty. >> >> or >> >> Enabling this parameter may incur a noticeable performance penalty, >> especially when a fewer kinds of queries are executed on many >> concurrent connections. > > Something seems is wrong with this sentence, and I'm not sure what it's trying > to say. Is this right ? pg_stat_statements users different spinlock for each kind of query. So fewer kinds of queries many sessions execute, fewer spinlocks they try to acquire. This may lead to spinlock contention and significant performance degration. This is what the statement is trying to say. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Justin Pryzby <pryzby@telsasoft.com> — 2021-04-19T14:55:45Z
On Mon, Apr 19, 2021 at 11:44:05PM +0900, Fujii Masao wrote: > On 2021/04/19 8:36, Justin Pryzby wrote: > > Reviewing this change which was committed last year as > > 321fa6a4a26c9b649a0fbec9fc8b019f19e62289 > > > > On Fri, Jul 03, 2020 at 03:57:38PM +0900, Fujii Masao wrote: > > > On 2020/07/03 13:05, Pavel Stehule wrote: > > > > pá 3. 7. 2020 v 4:39 odesílatel Fujii Masao <masao.fujii@oss.nttdata.com> napsal: > > > > > > > > Maybe there can be documented so enabling this option can have a negative impact on performance. > > > > > > Yes. What about adding either of the followings into the doc? > > > > > > Enabling this parameter may incur a noticeable performance penalty. > > > > > > or > > > > > > Enabling this parameter may incur a noticeable performance penalty, > > > especially when a fewer kinds of queries are executed on many > > > concurrent connections. > > > > Something seems is wrong with this sentence, and I'm not sure what it's trying > > to say. Is this right ? > > pg_stat_statements users different spinlock for each kind of query. > So fewer kinds of queries many sessions execute, fewer spinlocks > they try to acquire. This may lead to spinlock contention and > significant performance degration. This is what the statement is > trying to say. What does "kind" mean ? I think it means a "normalized" query or a "query structure". "a fewer kinds" is wrong, so I think the docs should say "a small number of queries" or maybe: > > > Enabling this parameter may incur a noticeable performance penalty, > > > especially similar queries are run by many concurrent connections and > > > compete to update the same pg_stat_statements entry -- Justin
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2021-04-21T14:38:52Z
On 2021/04/19 23:55, Justin Pryzby wrote: > What does "kind" mean ? I think it means a "normalized" query or a "query > structure". > > "a fewer kinds" is wrong, so I think the docs should say "a small number of > queries" or maybe: Okay, I agree to update the description. >>>> Enabling this parameter may incur a noticeable performance penalty, >>>> especially similar queries are run by many concurrent connections and >>>> compete to update the same pg_stat_statements entry "a small number of" is better than "similar" at the above because "similar" sounds a bit unclear in this case? It's better to use "entries" rather than "entry" at the above? Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Justin Pryzby <pryzby@telsasoft.com> — 2021-04-21T14:53:38Z
On Wed, Apr 21, 2021 at 11:38:52PM +0900, Fujii Masao wrote: > On 2021/04/19 23:55, Justin Pryzby wrote: > > What does "kind" mean ? I think it means a "normalized" query or a "query > > structure". > > > > "a fewer kinds" is wrong, so I think the docs should say "a small number of > > queries" or maybe: > > Okay, I agree to update the description. > > > > > > Enabling this parameter may incur a noticeable performance penalty, > > > > > especially similar queries are run by many concurrent connections and > > > > > compete to update the same pg_stat_statements entry > > "a small number of" is better than "similar" at the above because > "similar" sounds a bit unclear in this case? > > It's better to use "entries" rather than "entry" at the above? How about like this? Enabling this parameter may incur a noticeable performance penalty, - especially when a fewer kinds of queries are executed on many + especially when queries with the same queryid are executed by many concurrent connections. Or: Enabling this parameter may incur a noticeable performance penalty, especially similar queries are executed by many concurrent connections and compete to update a small number of pg_stat_statements entries. -- Justin -
Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2021-04-21T15:13:17Z
On 2021/04/21 23:53, Justin Pryzby wrote: > Or: > > Enabling this parameter may incur a noticeable performance penalty, > especially similar queries are executed by many concurrent connections > and compete to update a small number of pg_stat_statements entries. I prefer this. But what about using "identical" instead of "similar" because pg_stat_statements docs already uses "identical" in some places? Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Justin Pryzby <pryzby@telsasoft.com> — 2021-04-21T15:40:07Z
On Thu, Apr 22, 2021 at 12:13:17AM +0900, Fujii Masao wrote: > On 2021/04/21 23:53, Justin Pryzby wrote: > > Or: > > > > Enabling this parameter may incur a noticeable performance penalty, > > especially similar queries are executed by many concurrent connections > > and compete to update a small number of pg_stat_statements entries. > > I prefer this. But what about using "identical" instead of "similar" > because pg_stat_statements docs already uses "identical" in some places? I also missed "when", again... > > Enabling this parameter may incur a noticeable performance penalty, > > especially when queries with identical structure are executed by many concurrent connections > > which compete to update a small number of pg_stat_statements entries.
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Re: track_planning causing performance regression
Justin Pryzby <pryzby@telsasoft.com> — 2021-06-29T02:09:18Z
On Wed, Apr 21, 2021 at 10:40:07AM -0500, Justin Pryzby wrote: > On Thu, Apr 22, 2021 at 12:13:17AM +0900, Fujii Masao wrote: > > On 2021/04/21 23:53, Justin Pryzby wrote: > > > Or: > > > > > > Enabling this parameter may incur a noticeable performance penalty, > > > especially similar queries are executed by many concurrent connections > > > and compete to update a small number of pg_stat_statements entries. > > > > I prefer this. But what about using "identical" instead of "similar" > > because pg_stat_statements docs already uses "identical" in some places? > > I also missed "when", again... > > > > Enabling this parameter may incur a noticeable performance penalty, > > > especially when queries with identical structure are executed by many concurrent connections > > > which compete to update a small number of pg_stat_statements entries. Checking back - here's the latest patch. diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml index 930081c429..9e98472c5c 100644 --- a/doc/src/sgml/pgstatstatements.sgml +++ b/doc/src/sgml/pgstatstatements.sgml @@ -696,8 +696,9 @@ <varname>pg_stat_statements.track_planning</varname> controls whether planning operations and duration are tracked by the module. Enabling this parameter may incur a noticeable performance penalty, - especially when queries with the same queryid are executed on many - concurrent connections. + especially when queries with identical structure are executed by many + concurrent connections which compete to update a small number of + pg_stat_statements entries. The default value is <literal>off</literal>. Only superusers can change this setting. </para> -
Re: track_planning causing performance regression
Julien Rouhaud <rjuju123@gmail.com> — 2021-06-29T02:29:43Z
On Tue, Jun 29, 2021 at 10:09 AM Justin Pryzby <pryzby@telsasoft.com> wrote: > > Checking back - here's the latest patch. > > diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml > index 930081c429..9e98472c5c 100644 > --- a/doc/src/sgml/pgstatstatements.sgml > +++ b/doc/src/sgml/pgstatstatements.sgml > @@ -696,8 +696,9 @@ > <varname>pg_stat_statements.track_planning</varname> controls whether > planning operations and duration are tracked by the module. > Enabling this parameter may incur a noticeable performance penalty, > - especially when queries with the same queryid are executed on many > - concurrent connections. > + especially when queries with identical structure are executed by many > + concurrent connections which compete to update a small number of > + pg_stat_statements entries. > The default value is <literal>off</literal>. > Only superusers can change this setting. > </para> Is "identical structure" really accurate here? For instance a multi tenant application could rely on the search_path and only use unqualified relation name. So while they have queries with identical structure, those will generate a large number of different query_id.
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Re: track_planning causing performance regression
Justin Pryzby <pryzby@telsasoft.com> — 2021-06-29T02:45:35Z
On Tue, Jun 29, 2021 at 10:29:43AM +0800, Julien Rouhaud wrote: > On Tue, Jun 29, 2021 at 10:09 AM Justin Pryzby <pryzby@telsasoft.com> wrote: > > Is "identical structure" really accurate here? For instance a multi > tenant application could rely on the search_path and only use > unqualified relation name. So while they have queries with identical > structure, those will generate a large number of different query_id. We borrowed that language from the previous text: | Plannable queries (that is, SELECT, INSERT, UPDATE, and DELETE) are combined into a single pg_stat_statements entry whenever they have identical query structures according to an internal hash calculation Note that it continues to say: |In some cases, queries with visibly different texts might get merged into a single pg_stat_statements entry. Normally this will happen only for semantically equivalent queries, but there is a small chance of hash collisions causing unrelated queries to be merged into one entry. (This cannot happen for queries belonging to different users or databases, however.) | |Since the queryid hash value is computed on the post-parse-analysis representation of the queries, the opposite is also possible: queries with identical texts might appear as separate entries, if they have different meanings as a result of factors such as different search_path settings. Really, I'm only trying to fix where it currently says "a fewer kinds". It looks like I'd sent the wrong diff (git diff with a previous patch applied). I think this is the latest proposal: Enabling this parameter may incur a noticeable performance penalty, - especially when a fewer kinds of queries are executed on many - concurrent connections. + especially when queries with identical structure are executed by many + concurrent connections which compete to update a small number of + pg_stat_statements entries. It could say "identical structure" or "the same queryid" or "identical queryid". -- Justin -
Re: track_planning causing performance regression
Julien Rouhaud <rjuju123@gmail.com> — 2021-06-29T15:12:36Z
On Tue, Jun 29, 2021 at 10:45 AM Justin Pryzby <pryzby@telsasoft.com> wrote: > > We borrowed that language from the previous text: > > | Plannable queries (that is, SELECT, INSERT, UPDATE, and DELETE) are combined into a single pg_stat_statements entry whenever they have identical query structures according to an internal hash calculation Yes, but here's it's "identical query structure", which seems less ambiguous than "identical structure" as iI think one could think it refer to internal representation as much as as the query text. And it's also removing any doubt with the final "internal hash calculation". > Really, I'm only trying to fix where it currently says "a fewer kinds". I agree that "fewer kinds" should be improved. > Enabling this parameter may incur a noticeable performance penalty, > - especially when a fewer kinds of queries are executed on many > - concurrent connections. > + especially when queries with identical structure are executed by many > + concurrent connections which compete to update a small number of > + pg_stat_statements entries. > > It could say "identical structure" or "the same queryid" or "identical queryid". I think we should try to reuse the previous formulation. How about "statements with identical query structure"? Or replace query structure with "internal representation", in both places?
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2021-07-01T08:28:30Z
On 2021/06/30 0:12, Julien Rouhaud wrote: >> Enabling this parameter may incur a noticeable performance penalty, >> - especially when a fewer kinds of queries are executed on many >> - concurrent connections. >> + especially when queries with identical structure are executed by many >> + concurrent connections which compete to update a small number of >> + pg_stat_statements entries. >> >> It could say "identical structure" or "the same queryid" or "identical queryid". > > I think we should try to reuse the previous formulation. How about > "statements with identical query structure"? I'm fine with this. So what about the following diff? I added <structname> tag. <varname>pg_stat_statements.track_planning</varname> controls whether planning operations and duration are tracked by the module. Enabling this parameter may incur a noticeable performance penalty, - especially when a fewer kinds of queries are executed on many - concurrent connections. + especially when statements with identical query structure are executed + by many concurrent connections which compete to update a small number of + <structname>pg_stat_statements</structname> entries. The default value is <literal>off</literal>. Only superusers can change this setting. Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION -
Re: track_planning causing performance regression
Julien Rouhaud <rjuju123@gmail.com> — 2021-07-07T09:09:21Z
On Thu, Jul 1, 2021 at 4:28 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > I'm fine with this. So what about the following diff? I added <structname> tag. > > <varname>pg_stat_statements.track_planning</varname> controls whether > planning operations and duration are tracked by the module. > Enabling this parameter may incur a noticeable performance penalty, > - especially when a fewer kinds of queries are executed on many > - concurrent connections. > + especially when statements with identical query structure are executed > + by many concurrent connections which compete to update a small number of > + <structname>pg_stat_statements</structname> entries. > The default value is <literal>off</literal>. > Only superusers can change this setting. It seems perfect, thanks!
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Re: track_planning causing performance regression
Fujii Masao <masao.fujii@oss.nttdata.com> — 2021-07-07T12:57:37Z
On 2021/07/07 18:09, Julien Rouhaud wrote: > On Thu, Jul 1, 2021 at 4:28 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: >> >> I'm fine with this. So what about the following diff? I added <structname> tag. >> >> <varname>pg_stat_statements.track_planning</varname> controls whether >> planning operations and duration are tracked by the module. >> Enabling this parameter may incur a noticeable performance penalty, >> - especially when a fewer kinds of queries are executed on many >> - concurrent connections. >> + especially when statements with identical query structure are executed >> + by many concurrent connections which compete to update a small number of >> + <structname>pg_stat_statements</structname> entries. >> The default value is <literal>off</literal>. >> Only superusers can change this setting. > > It seems perfect, thanks! Pushed. Thanks! Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
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Re: track_planning causing performance regression
Julien Rouhaud <rjuju123@gmail.com> — 2021-07-07T13:05:33Z
On Wed, Jul 7, 2021 at 8:57 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote: > > Pushed. Thanks! Thanks!