Horton

Re: Skipping logical replication transactions on subscriber side

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Noah Misch <noah@leadboat.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Euler Taveira <euler@eulerto.com>, "osumi.takamichi@fujitsu.com" <osumi.takamichi@fujitsu.com>, "David G. Johnston" <david.g.johnston@gmail.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, vignesh C <vignesh21@gmail.com>, Greg Nancarrow <gregn4422@gmail.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, Alexey Lesovsky <lesovsky@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2022-06-22T14:53:07Z
Lists: pgsql-hackers 
On Wed, Jun 22, 2022 at 10:39 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> That's a fundamental misreading of the situation.  typalign is essential
> on alignment-picky architectures, else you will get a SIGBUS fault
> when trying to fetch a multibyte value (whether it's just going to get
> stored into a Datum array is not very relevant here).

I mean, that problem is easily worked around. Maybe you think memcpy
would be a lot slower than a direct assignment, but "essential" is a
strong word.

> I concur that Noah's description of #2 is not an accurate statement
> of the rules we'd have to impose to be sure that the C structs line up
> with the actual tuple layouts.  I don't think we want rules exactly,
> what we need is mechanical verification that the field orderings in
> use are safe.  The last time I looked at this thread, what was being
> discussed was (a) re-ordering pg_subscription's columns and (b)
> adding some kind of regression test to verify that all catalogs meet
> the expectation of 'd'-aligned fields not needing alignment padding
> that an AIX compiler might choose not to insert.  That still seems
> like the most plausible answer to me.  I don't especially want to
> invent an additional typalign code that we could only test on legacy
> platforms.

I agree with that, but I don't think that having the developers
enforce alignment rules by reordering catalog columns for the sake of
legacy platforms is appealing either.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

Commits

  1. Test ALIGNOF_DOUBLE==4 compatibility under ALIGNOF_DOUBLE==8.

  2. Reorder subskiplsn in pg_subscription to avoid alignment issues.

  3. Add ALTER SUBSCRIPTION ... SKIP.

  4. Optionally disable subscriptions on error.

  5. Update docs of logical replication for commit 8d74fc96db.

  6. Respect permissions within logical replication.

  7. Fix regression test failure caused by commit 8d74fc96db.

  8. Add a view to show the stats of subscription workers.

  9. Add logical change details to logical replication worker errcontext.

  10. Rename LOGICAL_REP_MSG_STREAM_END to LOGICAL_REP_MSG_STREAM_STOP.

  11. Fix typo in protocol.sgml.

  12. Remove unused argument in apply_handle_commit_internal().

  13. Fix replication of in-progress transactions in tablesync worker.

  14. Reorder pg_sequence columns to avoid alignment issue