Horton

Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions

Amit Kapila <amit.kapila16@gmail.com>

View thread
From: Amit Kapila <amit.kapila16@gmail.com>
To: Ajin Cherian <itsajin@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Erik Rijkers <er@xs4all.nl>, Kuntal Ghosh <kuntalghosh.2007@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Michael Paquier <michael@paquier.xyz>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-07-30T09:53:24Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Tighten the concurrent abort check during decoding.

  2. Improve hash_create()'s API for some added robustness.

  3. Use HASH_BLOBS for xidhash.

  4. Fix initialization of RelationSyncEntry for streaming transactions.

  5. Remove unused function declaration in logicalproto.h.

  6. Add additional tests to test streaming of in-progress transactions.

  7. Fix inline marking introduced in commit 464824323e.

  8. Add support for streaming to built-in logical replication.

  9. Fix the SharedFileSetUnregister API.

  10. Fix comment in procarray.c

  11. Suppress compiler warning in non-cassert builds.

  12. Extend the BufFile interface.

  13. Mark a few logical decoding related variables with PGDLLIMPORT.

  14. Implement streaming mode in ReorderBuffer.

  15. Extend the logical decoding output plugin API with stream methods.

  16. WAL Log invalidations at command end with wal_level=logical.

  17. Immediately WAL-log subtransaction and top-level XID association.

  18. Allow logical replication to transfer data in binary format.

  19. Only superuser can set sslcert/sslkey in postgres_fdw user mappings

  20. Track statistics for spilling of changes from ReorderBuffer.

  21. Add logical_decoding_work_mem to limit ReorderBuffer memory usage.

  22. logical decoding: process ASSIGNMENT during snapshot build

  23. Emit invalidations to standby for transactions without xid.

On Thu, Jul 30, 2020 at 12:28 PM Ajin Cherian <itsajin@gmail.com> wrote:
>
> I was running some tests on this patch. I was generally trying to see how the patch affects logical replication when doing bulk inserts. This issue has been raised in the past, for eg: this [1].
> My test setup is:
> 1. Two postgres servers running - A and B
> 2. Create a pgbench setup on A. (pgbench -i -s 5 postgres)
> 3. replicate the 3 tables (schema only) on B.
> 4. Three publishers on A for the 3 tables of pgbench; pgbench_accounts, pgbench_branches and pgbench_tellers;
> 5. Three subscribers on B for the same tables. (streaming on and off based on the scenarios described below)
>
> run pgbench with : pgbench -c 4 -T 100 postgres
> While pgbench is running, Do a bulk insert on some other table not in the publication list (say t1); INSERT INTO t1 (select i FROM generate_series(1,10000000) i);
>
> Four scenarios:
> 1. Pgbench with logical replication enabled without bulk insert
> Avg TPS (out of 10 runs): 641 TPS
> 2.Pgbench without logical replication enabled with bulk insert (no pub/sub)
> Avg TPS (out of 10 runs): 665 TPS
> 3, Pgbench with logical replication enabled with bulk insert
> Avg TPS (out of 10 runs): 278 TPS
> 4. Pgbench with logical replication streaming on with bulk insert
> Avg TPS (out of 10 runs): 440 TPS
>
> As you can see, the bulk inserts, although on a totally unaffected table, does impact the TPS. But what is good is that, enabling streaming improves the TPS (about 58% improvement)
>

Thanks for doing these tests, it is a good win and probably the reason
is that after patch we won't serialize such big transactions (as shown
in Konstantin's email [1]) and they will be simply skipped.
Basically, it will try to stream such transactions and will skip them
as they are not required to be sent.

[1] - https://www.postgresql.org/message-id/5f5143cc-9f73-3909-3ef7-d3895cc6cc90%40postgrespro.ru

-- 
With Regards,
Amit Kapila.