Re: Implement waiting for wal lsn replay: reloaded

Álvaro Herrera <alvherre@kurilemu.de>

From: Álvaro Herrera <alvherre@kurilemu.de>

To: Xuneng Zhou <xunengzhou@gmail.com>

Cc: Alexander Korotkov <aekorotkov@gmail.com>, Michael Paquier <michael@paquier.xyz>, jian he <jian.universality@gmail.com>, Tomas Vondra <tomas@vondra.me>, Yura Sokolov <y.sokolov@postgrespro.ru>, pgsql-hackers@lists.postgresql.org

Date: 2025-10-15T08:51:42Z

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 →

Clean up 019_replslot_limit.pl comments
- 0b866bb90368 19 (unreleased) landed
Stabilize 019_replslot_limit.pl: wait on slot restart_lsn
- cdb1d1cf1de6 19 (unreleased) landed
Use WAIT FOR LSN in PostgreSQL::Test::Cluster::wait_for_catchup()
- 7e8aeb9e483d 19 (unreleased) landed
- f30848cb05d4 19 (unreleased) landed
Add tab completion for the WAIT FOR LSN MODE option
- 76948337f724 19 (unreleased) landed
Add the MODE option to the WAIT FOR LSN command
- 49a181b5d634 19 (unreleased) landed
Extend xlogwait infrastructure with write and flush wait types
- 7a39f43d885b 19 (unreleased) landed
Unify error messages
- 502e256f2262 19 (unreleased) cited
Optimize shared memory usage for WaitLSNProcInfo
- 75e82b2f5a6f 19 (unreleased) landed
Fix WaitLSNWakeup() fast-path check for InvalidXLogRecPtr
- ede6acef4967 19 (unreleased) landed
Fix incorrect function name in comments
- 23792d738158 19 (unreleased) landed
Add infrastructure for efficient LSN waiting
- 3b4e53a075ea 19 (unreleased) landed
Add pairingheap_initialize() for shared memory usage
- 8af3ae0d4b36 19 (unreleased) landed
Implement WAIT FOR command
- 447aae13b030 19 (unreleased) landed

I didn't review the patch other than look at the grammar, but I disagree
with using opt_with in it.  I think WITH should be a mandatory word, or
just not be there at all.  The current formulation lets you do one of:

1. WAIT FOR LSN '123/456' WITH (opt = val);
2. WAIT FOR LSN '123/456' (opt = val);
3. WAIT FOR LSN '123/456';

and I don't see why you need two ways to specify an option list.

So one option is to remove opt_wait_with_clause and just use
opt_utility_option_list, which would remove the WITH keyword from there
(ie. only keep 2 and 3 from the above list).  But I think that's worse:
just look at the REPACK grammar[1], where we have to have additional
productions for the optional parenthesized option list.

So why not do just

+opt_wait_with_clause:
+           WITH '(' utility_option_list ')'        { $$ = $3; }
+           | /*EMPTY*/                             { $$ = NIL; }
+           ;

which keeps options 1 and 3 of the list above.

Note: you don't need to worry about WITH_LA, because that's only going
to show up when the user writes WITH TIME or WITH ORDINALITY (see
parser.c), and that's a syntax error anyway.


[1] https://postgr.es/m/202510101352.vvp4p3p2dblu@alvherre.pgsql

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
"La virtud es el justo medio entre dos defectos" (Aristóteles)