Horton

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

Tomas Vondra <tomas.vondra@2ndquadrant.com>

View thread
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2019-09-27T11:25:20Z
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 Fri, Sep 27, 2019 at 02:33:32PM +0530, Amit Kapila wrote:
>On Tue, Jan 9, 2018 at 7:55 AM Peter Eisentraut
><peter.eisentraut@2ndquadrant.com> wrote:
>>
>> 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?
>>
>
>Having a separate variable for this can give more flexibility, but
>OTOH it will add one more knob which user might not have a good idea
>to set.  What are the problems we see if directly use work_mem for
>this case?
>

IMHO it's similar to autovacuum_work_mem - we have an independent
setting, but most people use it as -1 so we use maintenance_work_mem as
a default value. I think it makes sense to do the same thing here.

It does ad an extra knob anyway (I don't think we should just use
maintenance_work_mem directly, the user should have an option to
override it when needed). But most users will not notice.

FWIW I don't think we should use work_mem, maintenace_work_mem seems
somewhat more appropriate here (not related to queries, etc.).

>If we can't use work_mem, then I think the name proposed by you
>(logical_decoding_work_mem) sounds good to me.
>

Yes, that name seems better.


regards

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