Horton

Re: Minimal logical decoding on standbys

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Amit Khandekar <amitdkhan.pg@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, tushar <tushar.ahuja@enterprisedb.com>, Petr Jelinek <petr.jelinek@2ndquadrant.com>, Craig Ringer <craig@2ndquadrant.com>, Petr Jelinek <petr@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2019-05-23T13:16:34Z
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. Reduce the log level in 035_standby_logical_decoding.pl.

  2. 035_standby_logical_decoding: Add missing waits for replication

  3. For cascading replication, wake physical and logical walsenders separately

  4. Handle logical slot conflicts on standby

  5. Support invalidating replication slots due to horizon and wal_level

  6. Prevent use of invalidated logical slot in CreateDecodingContext()

  7. Replace replication slot's invalidated_at LSN with an enum

  8. Pass down table relation into more index relation functions

  9. Assert only valid flag bits are passed to visibilitymap_set()

  10. Remove unused _bt_delitems_delete() argument.

  11. Add xl_btree_delete optimization.

On Thu, May 23, 2019 at 8:08 AM Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
> This made me think more of the race conditions. For instance, in
> pg_create_logical_replication_slot(), just after
> CheckLogicalDecodingRequirements and before actually creating the
> slot, suppose concurrently Controlfile->wal_level is changed from
> logical to replica.  So suppose a new slot does get created. Later the
> slot is read, so in pg_logical_slot_get_changes_guts(),
> CheckLogicalDecodingRequirements() is called where it checks
> ControlFile->wal_level value. But just before it does that,
> ControlFile->wal_level concurrently changes back to logical, because
> of replay of another param-change record. So this logical reader will
> think that the wal_level is sufficient, and will proceed to read the
> records, but those records are *before* the wal_level change, so these
> records don't have logical data.
>
> Do you think this is possible, or I am missing something?

wal_level is PGC_POSTMASTER.

-- 
Robert Haas
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