Horton

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

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Erik Rijkers <er@xs4all.nl>, Jeff Janes <jeff.janes@gmail.com>, Kuntal Ghosh <kuntalghosh.2007@gmail.com>, Michael Paquier <michael@paquier.xyz>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Tomas Vondra <tomas.vondra@2ndquadrant.com>
Date: 2020-12-09T09:26:25Z
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.

Attachments

On Wed, Dec 02, 2020 at 01:50:25PM +0530, Amit Kapila wrote:
> On Wed, Dec 2, 2020 at 1:20 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > > On Mon, Nov 30, 2020 at 6:49 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > > > On Mon, Nov 30, 2020 at 3:14 AM Noah Misch <noah@leadboat.com> wrote:
> > > > > On Mon, Sep 07, 2020 at 12:00:41PM +0530, Amit Kapila wrote:
> > > > > > Thanks, I have pushed the last patch. Let's wait for a day or so to
> > > > > > see the buildfarm reports
> > > > >
> > > > > https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=sungazer&dt=2020-09-08%2006%3A24%3A14
> > > > > failed the new 015_stream.pl test with the subscriber looping like this:
> > > > >
> > > > > 2020-09-08 11:22:49.848 UTC [13959252:1] LOG:  logical replication apply worker for subscription "tap_sub" has started
> > > > > 2020-09-08 11:22:54.045 UTC [13959252:2] ERROR:  could not open temporary file "16393-510.changes.0" from BufFile "16393-510.changes": No such file or directory
> > > > > 2020-09-08 11:22:54.055 UTC [7602182:1] LOG:  logical replication apply worker for subscription "tap_sub" has started
> > > > > 2020-09-08 11:22:54.101 UTC [31785284:4] LOG:  background worker "logical replication worker" (PID 13959252) exited with exit code 1
> > > > > 2020-09-08 11:23:01.142 UTC [7602182:2] ERROR:  could not open temporary file "16393-510.changes.0" from BufFile "16393-510.changes": No such file or directory
> > > > > ...

> > > > The above kind of error can happen due to the following reasons: (a)
> > > > the first time we sent the stream and created the file and that got
> > > > removed before the second stream reached the subscriber. (b) from the
> > > > publisher-side, we never sent the indication that it is the first
> > > > stream and the subscriber directly tries to open the file thinking it
> > > > is already there.

Further testing showed it was a file location problem, not a deletion problem.
The worker tried to open
base/pgsql_tmp/pgsql_tmp9896408.1.sharedfileset/16393-510.changes.0, but these
were the files actually existing:

[nm@power-aix 0:2 2020-12-08T13:56:35 64gcc 0]$ ls -la $(find src/test/subscription/tmp_check -name '*sharedfileset*')
src/test/subscription/tmp_check/t_015_stream_subscriber_data/pgdata/base/pgsql_tmp/pgsql_tmp9896408.0.sharedfileset:
total 408
drwx------    2 nm       usr             256 Dec 08 03:20 .
drwx------    4 nm       usr             256 Dec 08 03:20 ..
-rw-------    1 nm       usr          207806 Dec 08 03:20 16393-510.changes.0

src/test/subscription/tmp_check/t_015_stream_subscriber_data/pgdata/base/pgsql_tmp/pgsql_tmp9896408.1.sharedfileset:
total 0
drwx------    2 nm       usr             256 Dec 08 03:20 .
drwx------    4 nm       usr             256 Dec 08 03:20 ..
-rw-------    1 nm       usr               0 Dec 08 03:20 16393-511.changes.0

> > I have executed "make check" in the loop with only this file.  I have
> > repeated it 5000 times but no failure, I am wondering shall we try to
> > execute in the same machine in a loop where it failed once?
> 
> Yes, that might help. Noah, would it be possible for you to try that

The problem is xidhash using strcmp() to compare keys; it needs memcmp().  For
this to matter, xidhash must contain more than one element.  Existing tests
rarely exercise the multi-element scenario.  Under heavy load, on this system,
the test publisher can have two active transactions at once, in which case it
does exercise multi-element xidhash.  (The publisher is sensitive to timing,
but the subscriber is not; once WAL contains interleaved records of two XIDs,
the subscriber fails every time.)  This would be much harder to reproduce on a
little-endian system, where strcmp(&xid, &xid_plus_one)!=0.  On big-endian,
every small XID has zero in the first octet; they all look like empty strings.

The attached patch has the one-line fix and some test suite changes that make
this reproduce frequently on any big-endian system.  I'm currently planning to
drop the test suite changes from the commit, but I could keep them if folks
like them.  (They'd need more comments and timeout handling.)