Horton

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

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

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
Cc: Alexey Kondratov <a.kondratov@postgrespro.ru>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Erik Rijkers <er@xs4all.nl>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2019-09-16T20:57:19Z
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 Mon, Sep 16, 2019 at 10:29:18PM +0300, Konstantin Knizhnik wrote:
>
>
>On 16.09.2019 19:54, Alexey Kondratov wrote:
>>On 30.08.2019 18:59, Konstantin Knizhnik wrote:
>>>
>>>I think that instead of defining savepoints it is simpler and more 
>>>efficient to use
>>>
>>>BeginInternalSubTransaction + 
>>>ReleaseCurrentSubTransaction/RollbackAndReleaseCurrentSubTransaction
>>>
>>>as it is done in PL/pgSQL (pl_exec.c).
>>>Not sure if it can pr
>>>
>>
>>Both BeginInternalSubTransaction and DefineSavepoint use 
>>PushTransaction() internally for a normal subtransaction start. So 
>>they seems to be identical from the performance perspective, which 
>>is also stated in the comment section:
>
>Yes, definitely them are using the same mechanism and most likely 
>provides similar performance.
>But BeginInternalSubTransaction does not require to generate some 
>savepoint name which seems to be redundant in this case.
>
>
>>
>>Anyway, I've performed a profiling of my apply worker (flamegraph is 
>>attached) and it spends the vast amount of time (>90%) applying 
>>changes. So the problem is not in the savepoints their-self, but in 
>>the fact that we first apply all changes and then abort all the 
>>work. Not sure, that it is possible to do something in this case.
>>
>
>Looks like the only way to increase apply speed is to do it in 
>parallel: make it possible to concurrently execute non-conflicting 
>transactions.
>

True, although it seems like a massive can of worms to me. I'm not aware
a way to identify non-conflicting transactions in advance, so it would
have to be implemented as optimistic apply, with a detection and
recovery from conflicts.

I'm not against doing that, and I'm willing to spend some time on revies
etc. but it seems like a completely separate effort.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
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