Horton

Re: Minimal logical decoding on standbys

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Amit Khandekar <amitdkhan.pg@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Craig Ringer <craig@2ndquadrant.com>, Petr Jelinek <petr@2ndquadrant.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2019-04-02T16:04:14Z
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.

Hi,

On 2019-04-02 15:26:52 +0530, Amit Khandekar wrote:
> On Thu, 14 Mar 2019 at 15:00, Amit Khandekar <amitdkhan.pg@gmail.com> wrote:
> > I managed to get a recovery conflict by :
> > 1. Setting hot_standby_feedback to off
> > 2. Creating a logical replication slot on standby
> > 3. Creating a table on master, and insert some data.
> > 2. Running : VACUUM FULL;
> >
> > This gives WARNING messages in the standby log file.
> > 2019-03-14 14:57:56.833 IST [40076] WARNING:  slot decoding_standby w/
> > catalog xmin 474 conflicts with removed xid 477
> > 2019-03-14 14:57:56.833 IST [40076] CONTEXT:  WAL redo at 0/3069E98
> > for Heap2/CLEAN: remxid 477
> >
> > But I did not add such a testcase into the test file, because with the
> > current patch, it does not do anything with the slot; it just keeps on
> > emitting WARNING in the log file; so we can't test this scenario as of
> > now using the tap test.
> 
> I am going ahead with drop-the-slot way of handling the recovery
> conflict. I am trying out using ReplicationSlotDropPtr() to drop the
> slot. It seems the required locks are already in place inside the for
> loop of ResolveRecoveryConflictWithSlots(), so we can directly call
> ReplicationSlotDropPtr() when the slot xmin conflict is found.

Cool.


> As explained above, the only way I could reproduce the conflict is by
> turning hot_standby_feedback off on slave, creating and inserting into
> a table on master and then running VACUUM FULL. But after doing this,
> I am not able to verify whether the slot is dropped, because on slave,
> any simple psql command thereon, waits on a lock acquired on sys
> catache, e.g. pg_authid. Working on it.

I think that indicates a bug somewhere. If replay progressed, it should
have killed the slot, and continued replaying past the VACUUM
FULL. Those symptoms suggest replay is stuck somewhere. I suggest a)
compiling with WAL_DEBUG enabled, and turning on wal_debug=1, b) looking
at a backtrace of the startup process.

Greetings,

Andres Freund