Horton

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

Erik Rijkers <er@xs4all.nl>

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From: Erik Rijkers <er@xs4all.nl>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2017-12-24T09:00:00Z
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.

>>>> 
>>>> logical replication of 2 instances is OK but 3 and up fail with:
>>>> 
>>>> TRAP: FailedAssertion("!(last_lsn < change->lsn)", File:
>>>> "reorderbuffer.c", Line: 1773)
>>>> 
>>>> I can cobble up a script but I hope you have enough from the 
>>>> assertion
>>>> to see what's going wrong...
>>> 
>>> The assertion says that the iterator produces changes in order that 
>>> does
>>> not correlate with LSN. But I have a hard time understanding how that
>>> could happen, particularly because according to the line number this
>>> happens in ReorderBufferCommit(), i.e. the current (non-streaming) 
>>> case.
>>> 
>>> So instructions to reproduce the issue would be very helpful.
>> 
>> Using:
>> 
>> 0001-Introduce-logical_work_mem-to-limit-ReorderBuffer-v2.patch
>> 0002-Issue-XLOG_XACT_ASSIGNMENT-with-wal_level-logical-v2.patch
>> 0003-Issue-individual-invalidations-with-wal_level-log-v2.patch
>> 0004-Extend-the-output-plugin-API-with-stream-methods-v2.patch
>> 0005-Implement-streaming-mode-in-ReorderBuffer-v2.patch
>> 0006-Add-support-for-streaming-to-built-in-replication-v2.patch
>> 
>> As you expected the problem is the same with these new patches.
>> 
>> I have now tested more, and seen that it not always fails.  I guess 
>> that
>> it here fails 3 times out of 4.  But the laptop I'm using at the 
>> moment
>> is old and slow -- it may well be a factor as we've seen before [1].
>> 
>> Attached is the bash that I put together.  I tested with
>> NUM_INSTANCES=2, which yields success, and NUM_INSTANCES=3, which 
>> fails
>> often.  This same program run with HEAD never seems to fail (I tried a
>> few dozen times).
>> 
> 
> Thanks. Unfortunately I still can't reproduce the issue. I even tried
> running it in valgrind, to see if there are some memory access issues
> (which should also slow it down significantly).

One wonders again if 2ndquadrant shouldn't invest in some old hardware 
;)

Another Good Thing would be if there was a provision in the buildfarm to 
test patches like these.

But I'm probably not to first one to suggest that; no doubt it'll be 
possible someday.  In the meantime I'll try to repeat this crash on 
other machines (but that will be after the holidays).


Erik Rijkers