Horton

Re: Logical walsenders don't process XLOG_CHECKPOINT_SHUTDOWN

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Julien Rouhaud <rjuju123@gmail.com>, Michael Paquier <michael@paquier.xyz>
Date: 2023-07-25T17:03:19Z
Lists: pgsql-hackers 
Hi,

On 2023-07-25 14:31:00 +0530, Amit Kapila wrote:
> To ensure that all the data has been sent during the upgrade, we can
> ensure that each logical slot's confirmed_flush_lsn (position in the
> WAL till which subscriber has confirmed that it has applied the WAL)
> is the same as current_wal_insert_lsn. Now, because we don't send
> XLOG_CHECKPOINT_SHUTDOWN even on clean shutdown, confirmed_flush_lsn
> will never be the same as current_wal_insert_lsn. The one idea being
> discussed in patch [1] (see 0003) is to ensure that each slot's LSN is
> exactly XLOG_CHECKPOINT_SHUTDOWN ago which probably has some drawbacks
> like what if we tomorrow add some other WAL in the shutdown checkpoint
> path or the size of record changes then we would need to modify the
> corresponding code in upgrade.

Yea, that doesn't seem like a good path. But there is a variant that seems
better: We could just scan the end of the WAL for records that should have
been streamed out?

Greetings,

Andres Freund

Commits

  1. Migrate logical slots to the new node during an upgrade.

  2. Prevent possibility of panics during shutdown checkpoint.