Horton

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

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Michael Paquier <michael@paquier.xyz>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-03-06T04:49:24Z
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, Mar 5, 2020 at 11:20 PM Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
>
> On Wed, Mar 04, 2020 at 10:28:32AM +0530, Amit Kapila wrote:
> >
>
> Sure, there's a lot to discuss. And it's possible (likely) it's not
> feasible to get this into PG13. But I think it's still worth discussing
> it, instead of just punting it into the next CF right away.
>

That makes sense to me.

> >> There's been a tremendous amount of work done since I last
> >> worked on it, and a lot was discussed on this thread, so it'll take a
> >> while to get familiar with the new code ...
> >>
> >> The first thing I realized that WAL-logging of assignments in v12 does
> >> both the "old" logging (using dedicated message) and "new" with
> >> toplevel-XID embedded in the first message. Yes, the patch was wrong,
> >> because it eliminated all calls to ProcArrayApplyXidAssignment() and so
> >> it was trivial to crash the replica due to KnownAssignedXids overflow.
> >> But I don't think re-introducing XLOG_XACT_ASSIGNMENT message is the
> >> right fix.
> >>
> >> I actually proposed doing this (having both ways to log assignments) so
> >> that there's no regression risk with (wal_level < logical). But IIRC
> >> Andres objected to it, argumenting that we should not log the same piece
> >> of information in two very different ways at the same time (IIRC it was
> >> discussed on the FOSDEM dev meeting, so I don't have a link to share).
> >> And I do agree with him ...
> >>
> >
> >So, aren't we worried about the overhead of the amount of WAL and
> >performance impact for the transactions?  We might want to check the
> >pgbench read-write test to see if that will add any significant
> >overhead.
> >
>
> Well, sure. I agree we need to see how this affects performance, and
> I'll do some benchmarks (I think I did that when submitting the patch,
> but I don't recall the numbers / details).
>
> Isn't it a bit strange to log stuff twice, though, if we worry about
> performance? Surely that's more expensive than logging it just once. Of
> course, it might be useful if most systems need just the "old" way.
>
> I know it's going to be a bit hand-wavy, but I think embedding the
> assignments into existing WAL messages is about the cheapest way to log
> this. I would not expect this to be mesurably more expensive than what
> we have now, but I might be wrong.
>

I agree that this shouldn't be much expensive, but it is better to be
sure in that regard.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com