Horton

Re: Speed up Clog Access by increasing CLOG buffers

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2016-09-29T13:47:09Z
Lists: pgsql-hackers 
On Wed, Sep 28, 2016 at 9:10 PM, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
>> I feel like we must be missing something here.  If Dilip is seeing
>> huge speedups and you're seeing nothing, something is different, and
>> we don't know what it is.  Even if the test case is artificial, it
>> ought to be the same when one of you runs it as when the other runs
>> it.  Right?
>>
> Yes, definitely - we're missing something important, I think. One difference
> is that Dilip is using longer runs, but I don't think that's a problem (as I
> demonstrated how stable the results are).

It's not impossible that the longer runs could matter - performance
isn't necessarily stable across time during a pgbench test, and the
longer the run the more CLOG pages it will fill.

> I wonder what CPU model is Dilip using - I know it's x86, but not which
> generation it is. I'm using E5-4620 v1 Xeon, perhaps Dilip is using a newer
> model and it makes a difference (although that seems unlikely).

The fact that he's using an 8-socket machine seems more likely to
matter than the CPU generation, which isn't much different.  Maybe
Dilip should try this on a 2-socket machine and see if he sees the
same kinds of results.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Use group updates when setting transaction status in clog.

  2. Improve 64bit atomics support.

  3. Add ProcArrayGroupUpdate wait event.

  4. Make the different Unix-y semaphore implementations ABI-compatible.

  5. Fix broken ALTER INDEX documentation

  6. Code and docs review for commit 3187d6de0e5a9e805b27c48437897e8c39071d45.

  7. Partition the freelist for shared dynahash tables.

  8. Correct StartupSUBTRANS for page wraparound

  9. Make idle backends exit if the postmaster dies.

  10. contrib/sslinfo: add ssl_extension_info SRF

  11. Reduce ProcArrayLock contention by removing backends in batches.

  12. Fix `make installcheck` for serializable transactions.

  13. Lockless StrategyGetBuffer clock sweep hot path.

  14. Reduce sinval synchronization overhead.