Horton

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

Peter Eisentraut <peter.eisentraut@2ndquadrant.com>

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From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2018-01-09T02:24:55Z
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 1/3/18 14:53, Tomas Vondra wrote:
>> I don't see the need to tie this setting to maintenance_work_mem. 
>> maintenance_work_mem is often set to very large values, which could
>> then have undesirable side effects on this use.
> 
> Well, we need to pick some default value, and we can either use a fixed
> value (not sure what would be a good default) or tie it to an existing
> GUC. We only really have work_mem and maintenance_work_mem, and the
> walsender process will never use more than one such buffer. Which seems
> to be closer to maintenance_work_mem.
> 
> Pretty much any default value can have undesirable side effects.

Let's just make it an independent setting unless we know any better.  We
don't have a lot of settings that depend on other settings, and the ones
we do have a very specific relationship.

>> Moreover, the name logical_work_mem makes it sound like it's a logical
>> version of work_mem.  Maybe we could think of another name.
> 
> I won't object to a better name, of course. Any proposals?

logical_decoding_[work_]mem?

>> I think we need a way to report on how much memory is actually used,
>> so the setting can be tuned. Something analogous to log_temp_files
>> perhaps.
> 
> Yes, I agree. I'm just about to submit an updated version of the patch
> series, that also introduces a few columns pg_stat_replication, tracking
> this type of stats (amount of data spilled to disk or streamed, etc.).

That seems OK.  Perhaps we could bring forward the part of that patch
that applies to this feature.

That would also help testing *this* feature and determine what
appropriate settings are.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services