From: Alexander Korotkov <akorotkov@postgresql.org>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Add infrastructure for efficient LSN waiting
Date: Wed, 05 Nov 2025 09:44:46 +0000
Message-ID: <E1vGa4M-0058Gz-2g@gemulon.postgresql.org> (raw)
Add infrastructure for efficient LSN waiting
Implement a new facility that allows processes to wait for WAL to reach
specific LSNs, both on primary (waiting for flush) and standby (waiting
for replay) servers.
The implementation uses shared memory with per-backend information
organized into pairing heaps, allowing O(1) access to the minimum
waited LSN. This enables fast-path checks: after replaying or flushing
WAL, the startup process or WAL writer can quickly determine if any
waiters need to be awakened.
Key components:
- New xlogwait.c/h module with WaitForLSNReplay() and WaitForLSNFlush()
- Separate pairing heaps for replay and flush waiters
- WaitLSN lightweight lock for coordinating shared state
- Wait events WAIT_FOR_WAL_REPLAY and WAIT_FOR_WAL_FLUSH for monitoring
This infrastructure can be used by features that need to wait for WAL
operations to complete.
Discussion: https://www.postgresql.org/message-id/flat/CAPpHfdsjtZLVzxjGT8rJHCYbM0D5dwkO+BBjcirozJ6nYbOW8Q@mail....
Discussion: https://www.postgresql.org/message-id/flat/CABPTF7UNft368x-RgOXkfj475OwEbp%2BVVO-wEXz7StgjD_%3D6sw%4...
Author: Kartyshov Ivan <i.kartyshov@postgrespro.ru>
Author: Alexander Korotkov <aekorotkov@gmail.com>
Author: Xuneng Zhou <xunengzhou@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Alexander Lakhin <exclusion@gmail.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Euler Taveira <euler@eulerto.com>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Xuneng Zhou <xunengzhou@gmail.com>
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/3b4e53a075ea5671b075f8fd873241179f8e64af
Modified Files
--------------
src/backend/access/transam/Makefile | 3 +-
src/backend/access/transam/meson.build | 1 +
src/backend/access/transam/xlogwait.c | 409 ++++++++++++++++++++++++
src/backend/storage/ipc/ipci.c | 3 +
src/backend/utils/activity/wait_event_names.txt | 3 +
src/include/access/xlogwait.h | 98 ++++++
src/include/storage/lwlocklist.h | 1 +
src/tools/pgindent/typedefs.list | 4 +
8 files changed, 521 insertions(+), 1 deletion(-)
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To: pgsql-committers@postgresql.org
Cc: akorotkov@postgresql.org, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Add infrastructure for efficient LSN waiting
In-Reply-To: <E1vGa4M-0058Gz-2g@gemulon.postgresql.org>
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