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: Robert Haas <robertmhaas@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Michael Paquier <michael@paquier.xyz>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-01-03T09:24:26Z
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 Tue, Dec 24, 2019 at 10:58 AM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Thu, Dec 12, 2019 at 3:41 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> > I think the way invalidations work for logical replication is that
> > normally, we always start a new transaction before decoding each
> > commit which allows us to accept the invalidations (via
> > AtStart_Cache).  However, if there are catalog changes within the
> > transaction being decoded, we need to reflect those before trying to
> > decode the WAL of operation which happened after that catalog change.
> > As we are not logging the WAL for each invalidation, we need to
> > execute all the invalidation messages for this transaction at each
> > catalog change. We are able to do that now as we decode the entire WAL
> > for a transaction only once we get the commit's WAL which contains all
> > the invalidation messages.  So, we queue them up and execute them for
> > each catalog change which we identify by WAL record
> > XLOG_HEAP2_NEW_CID.
>
> Thanks for the explanation. That makes sense. But, it's still true,
> AFAICS, that instead of doing this stuff with logging invalidations
> you could just InvalidateSystemCaches() in the cases where you are
> currently applying all of the transaction's invalidations. That
> approach might be worse than changing the way invalidations are
> logged, but the two approaches deserve to be compared. One approach
> has more CPU overhead and the other has more WAL overhead, so it's a
> little hard to compare them, but it seems worth mulling over.
>

I have given some thought over it and it seems to me that this will
increase not only CPU usage but also Network usage.  The increase in
CPU usage will be for all WALSenders that decodes a transaction that
has performed DDL.  The increase in network usage comes from the fact
that we need to send the schema of relations again which doesn't
require to be invalidated.  It is because invalidation blew our local
map that remembers which relation schemas are sent.

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