Horton

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

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Ajin Cherian <itsajin@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Erik Rijkers <er@xs4all.nl>, Kuntal Ghosh <kuntalghosh.2007@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Michael Paquier <michael@paquier.xyz>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-07-10T05:11:19Z
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 Fri, Jul 10, 2020 at 9:21 AM Ajin Cherian <itsajin@gmail.com> wrote:
>
>
>
> On Thu, Jul 9, 2020 at 1:30 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>>
>>
>> > I think if the GUC is set then maybe we can bypass this check so that
>> > it can try to stream every single change?
>> >
>>
>> Yeah and probably we need to do something for the check "while
>> (rb->size >= logical_decoding_work_mem * 1024L)" as well.
>>
>>
> I have made this change, as discussed, the regression tests seem to run fine. I have added a debug that records the streaming for each transaction >number. I also had to bypass certain asserts in ReorderBufferLargestTopTXN() as now we are going through the entire list of transactions and not just picking the biggest transaction .

So if always_stream_logical is true then we are always going for the
streaming even if the size is not reached and that is good.  And if
always_stream_logical is set then we are setting ctx->streaming=true
that is also good.  So now I don't think we need to change this part
of the code, because when we bypass the memory limit and set the
ctx->streaming=true it will always select the streaming option unless
it is impossible.  With your changes sometimes due to incomplete toast
changes, if it can not pick the largest top txn for streaming it will
hang forever in the while loop, in that case, it should go for
spilling.

while (rb->size >= logical_decoding_work_mem * 1024L)
{
/*
* Pick the largest transaction (or subtransaction) and evict it from
* memory by streaming, if supported. Otherwise, spill to disk.
*/
if (ReorderBufferCanStream(rb) &&
(txn = ReorderBufferLargestTopTXN(rb)) != NULL)


-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com