Feedback-ID: ie0a040ee:Fastmail
Message-ID: <18c0fa64-0475-415e-a1bd-665d922c5201@eisentraut.org>
Date: Fri, 30 Aug 2024 21:42:20 +0200
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: pgsql: Implement pg_wal_replay_wait() stored procedure
To: Alexander Korotkov <akorotkov@postgresql.org>,
 pgsql-committers@lists.postgresql.org
References: <E1sZwuz-002NPQ-Lc@gemulon.postgresql.org>
Content-Language: en-US
From: Peter Eisentraut <peter@eisentraut.org>
In-Reply-To: <E1sZwuz-002NPQ-Lc@gemulon.postgresql.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Archived-At: 
 <https://www.postgresql.org/message-id/18c0fa64-0475-415e-a1bd-665d922c5201%40eisentraut.org>
Precedence: bulk

On 02.08.24 20:22, Alexander Korotkov wrote:
> Implement pg_wal_replay_wait() stored procedure

Why is this under src/backend/command/?  Wouldn't it belong under 
src/backend/utils/adt/?

> pg_wal_replay_wait() is to be used on standby and specifies waiting for
> the specific WAL location to be replayed.  This option is useful when
> the user makes some data changes on primary and needs a guarantee to see
> these changes are on standby.
> 
> The queue of waiters is stored in the shared memory as an LSN-ordered pairing
> heap, where the waiter with the nearest LSN stays on the top.  During
> the replay of WAL, waiters whose LSNs have already been replayed are deleted
> from the shared memory pairing heap and woken up by setting their latches.
> 
> pg_wal_replay_wait() needs to wait without any snapshot held.  Otherwise,
> the snapshot could prevent the replay of WAL records, implying a kind of
> self-deadlock.  This is why it is only possible to implement
> pg_wal_replay_wait() as a procedure working without an active snapshot,
> not a function.
> 
> Catversion is bumped.
> 
> Discussion: https://postgr.es/m/eb12f9b03851bb2583adab5df9579b4b%40postgrespro.ru
> Author: Kartyshov Ivan, Alexander Korotkov
> Reviewed-by: Michael Paquier, Peter Eisentraut, Dilip Kumar, Amit Kapila
> Reviewed-by: Alexander Lakhin, Bharath Rupireddy, Euler Taveira
> Reviewed-by: Heikki Linnakangas, Kyotaro Horiguchi
> 
> Branch
> ------
> master
> 
> Details
> -------
> https://git.postgresql.org/pg/commitdiff/3c5db1d6b01642bcd8dbf5e34b68f034365747bb
> 
> Modified Files
> --------------
> doc/src/sgml/func.sgml                          | 117 ++++++++
> src/backend/access/transam/xact.c               |   6 +
> src/backend/access/transam/xlog.c               |   7 +
> src/backend/access/transam/xlogrecovery.c       |  11 +
> src/backend/catalog/system_functions.sql        |   3 +
> src/backend/commands/Makefile                   |   3 +-
> src/backend/commands/meson.build                |   1 +
> src/backend/commands/waitlsn.c                  | 363 ++++++++++++++++++++++++
> src/backend/lib/pairingheap.c                   |  18 +-
> src/backend/storage/ipc/ipci.c                  |   3 +
> src/backend/storage/lmgr/proc.c                 |   6 +
> src/backend/tcop/pquery.c                       |   9 +-
> src/backend/utils/activity/wait_event_names.txt |   2 +
> src/include/catalog/catversion.h                |   2 +-
> src/include/catalog/pg_proc.dat                 |   6 +
> src/include/commands/waitlsn.h                  |  80 ++++++
> src/include/lib/pairingheap.h                   |   3 +
> src/include/storage/lwlocklist.h                |   1 +
> src/test/recovery/meson.build                   |   1 +
> src/test/recovery/t/043_wal_replay_wait.pl      | 150 ++++++++++
> src/tools/pgindent/typedefs.list                |   2 +
> 21 files changed, 786 insertions(+), 8 deletions(-)
>