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Commit772faaf

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Revert: Implement pg_wal_replay_wait() stored procedure
This commit reverts06c418e,e37662f,bf1e650,25f4242,ee79928, and74eaf66 per review by Heikki Linnakangas.Discussion:https://postgr.es/m/b155606b-e744-4218-bda5-29379779da1a%40iki.fi
1 parent922c4c4 commit772faaf

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20 files changed

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‎doc/src/sgml/func.sgml

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Original file line numberDiff line numberDiff line change
@@ -28770,119 +28770,6 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
2877028770
the pause, the rate of WAL generation and available disk space.
2877128771
</para>
2877228772

28773-
<para>
28774-
There are also procedures to control the progress of recovery.
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They are shown in <xref linkend="procedures-recovery-control-table"/>.
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These procedures may be executed only during recovery.
28777-
</para>
28778-
28779-
<table id="procedures-recovery-control-table">
28780-
<title>Recovery Control Procedures</title>
28781-
<tgroup cols="1">
28782-
<thead>
28783-
<row>
28784-
<entry role="func_table_entry"><para role="func_signature">
28785-
Procedure
28786-
</para>
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<para>
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Description
28789-
</para></entry>
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</row>
28791-
</thead>
28792-
28793-
<tbody>
28794-
<row>
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<entry role="func_table_entry"><para role="func_signature">
28796-
<indexterm>
28797-
<primary>pg_wal_replay_wait</primary>
28798-
</indexterm>
28799-
<function>pg_wal_replay_wait</function> (
28800-
<parameter>target_lsn</parameter> <type>pg_lsn</type>,
28801-
<parameter>timeout</parameter> <type>bigint</type> <literal>DEFAULT</literal> <literal>0</literal>)
28802-
<returnvalue>void</returnvalue>
28803-
</para>
28804-
<para>
28805-
If <parameter>timeout</parameter> is not specified or zero, this
28806-
procedure returns once WAL is replayed upto
28807-
<literal>target_lsn</literal>.
28808-
If the <parameter>timeout</parameter> is specified (in
28809-
milliseconds) and greater than zero, the procedure waits until the
28810-
server actually replays the WAL upto <literal>target_lsn</literal> or
28811-
until the given time has passed. On timeout, an error is emitted.
28812-
</para></entry>
28813-
</row>
28814-
</tbody>
28815-
</tgroup>
28816-
</table>
28817-
28818-
<para>
28819-
<function>pg_wal_replay_wait</function> waits till
28820-
<parameter>target_lsn</parameter> to be replayed on standby.
28821-
That is, after this function execution, the value returned by
28822-
<function>pg_last_wal_replay_lsn</function> should be greater or equal
28823-
to the <parameter>target_lsn</parameter> value. This is useful to achieve
28824-
read-your-writes-consistency, while using async replica for reads and
28825-
primary for writes. In that case <acronym>lsn</acronym> of the last
28826-
modification should be stored on the client application side or the
28827-
connection pooler side.
28828-
</para>
28829-
28830-
<para>
28831-
You can use <function>pg_wal_replay_wait</function> to wait for
28832-
the <type>pg_lsn</type> value. For example, an application could update
28833-
the <literal>movie</literal> table and get the <acronym>lsn</acronym> after
28834-
changes just made. This example uses <function>pg_current_wal_insert_lsn</function>
28835-
on primary server to get the <acronym>lsn</acronym> given that
28836-
<varname>synchronous_commit</varname> could be set to
28837-
<literal>off</literal>.
28838-
28839-
<programlisting>
28840-
postgres=# UPDATE movie SET genre = 'Dramatic' WHERE genre = 'Drama';
28841-
UPDATE 100
28842-
postgres=# SELECT pg_current_wal_insert_lsn();
28843-
pg_current_wal_insert_lsn
28844-
--------------------
28845-
0/306EE20
28846-
(1 row)
28847-
</programlisting>
28848-
28849-
Then an application could run <function>pg_wal_replay_wait</function>
28850-
with the <acronym>lsn</acronym> obtained from primary. After that the
28851-
changes made of primary should be guaranteed to be visible on replica.
28852-
28853-
<programlisting>
28854-
postgres=# CALL pg_wal_replay_wait('0/306EE20');
28855-
CALL
28856-
postgres=# SELECT * FROM movie WHERE genre = 'Drama';
28857-
genre
28858-
-------
28859-
(0 rows)
28860-
</programlisting>
28861-
28862-
It may also happen that target <acronym>lsn</acronym> is not achieved
28863-
within the timeout. In that case the error is thrown.
28864-
28865-
<programlisting>
28866-
postgres=# CALL pg_wal_replay_wait('0/306EE20', 100);
28867-
ERROR: timed out while waiting for target LSN 0/306EE20 to be replayed; current replay LSN 0/306EA60
28868-
</programlisting>
28869-
28870-
</para>
28871-
28872-
<para>
28873-
<function>pg_wal_replay_wait</function> can't be used within
28874-
the transaction, another procedure or function. Any of them holds a
28875-
snapshot, which could prevent the replay of WAL records.
28876-
28877-
<programlisting>
28878-
postgres=# BEGIN;
28879-
BEGIN
28880-
postgres=*# CALL pg_wal_replay_wait('0/306EE20');
28881-
ERROR: pg_wal_replay_wait() must be only called in non-atomic context
28882-
DETAIL: Make sure pg_wal_replay_wait() isn't called within a transaction, another procedure, or a function.
28883-
</programlisting>
28884-
28885-
</para>
2888628773
</sect2>
2888728774

2888828775
<sect2 id="functions-snapshot-synchronization">

‎src/backend/access/transam/xact.c

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@@ -38,7 +38,6 @@
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#include"commands/async.h"
3939
#include"commands/tablecmds.h"
4040
#include"commands/trigger.h"
41-
#include"commands/waitlsn.h"
4241
#include"common/pg_prng.h"
4342
#include"executor/spi.h"
4443
#include"libpq/be-fsstubs.h"
@@ -2772,11 +2771,6 @@ AbortTransaction(void)
27722771
*/
27732772
LWLockReleaseAll();
27742773

2775-
/*
2776-
* Cleanup waiting for LSN if any.
2777-
*/
2778-
WaitLSNCleanup();
2779-
27802774
/* Clear wait information and command progress indicator */
27812775
pgstat_report_wait_end();
27822776
pgstat_progress_end_command();

‎src/backend/access/transam/xlog.c

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@@ -66,7 +66,6 @@
6666
#include"catalog/catversion.h"
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#include"catalog/pg_control.h"
6868
#include"catalog/pg_database.h"
69-
#include"commands/waitlsn.h"
7069
#include"common/controldata_utils.h"
7170
#include"common/file_utils.h"
7271
#include"executor/instrument.h"
@@ -6130,12 +6129,6 @@ StartupXLOG(void)
61306129
UpdateControlFile();
61316130
LWLockRelease(ControlFileLock);
61326131

6133-
/*
6134-
* Wake up all waiters for replay LSN. They need to report an error that
6135-
* recovery was ended before achieving the target LSN.
6136-
*/
6137-
WaitLSNSetLatches(InvalidXLogRecPtr);
6138-
61396132
/*
61406133
* Shutdown the recovery environment. This must occur after
61416134
* RecoverPreparedTransactions() (see notes in lock_twophase_recover())

‎src/backend/access/transam/xlogrecovery.c

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@@ -43,7 +43,6 @@
4343
#include"backup/basebackup.h"
4444
#include"catalog/pg_control.h"
4545
#include"commands/tablespace.h"
46-
#include"commands/waitlsn.h"
4746
#include"common/file_utils.h"
4847
#include"miscadmin.h"
4948
#include"pgstat.h"
@@ -1829,16 +1828,6 @@ PerformWalRecovery(void)
18291828
break;
18301829
}
18311830

1832-
/*
1833-
* If we replayed an LSN that someone was waiting for then walk
1834-
* over the shared memory array and set latches to notify the
1835-
* waiters.
1836-
*/
1837-
if (waitLSN&&
1838-
(XLogRecoveryCtl->lastReplayedEndRecPtr >=
1839-
pg_atomic_read_u64(&waitLSN->minWaitedLSN)))
1840-
WaitLSNSetLatches(XLogRecoveryCtl->lastReplayedEndRecPtr);
1841-
18421831
/* Else, try to fetch the next WAL record */
18431832
record=ReadRecord(xlogprefetcher,LOG, false,replayTLI);
18441833
}while (record!=NULL);

‎src/backend/catalog/system_functions.sql

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@@ -414,9 +414,6 @@ CREATE OR REPLACE FUNCTION
414414
json_populate_recordset(base anyelement, from_json json, use_json_as_textboolean DEFAULT false)
415415
RETURNS SETOF anyelement LANGUAGE internal STABLE ROWS100AS'json_populate_recordset' PARALLEL SAFE;
416416

417-
CREATEOR REPLACE PROCEDURE pg_wal_replay_wait(target_lsn pg_lsn, timeout int8 DEFAULT0)
418-
LANGUAGE internalAS'pg_wal_replay_wait';
419-
420417
CREATE OR REPLACEFUNCTIONpg_logical_slot_get_changes(
421418
IN slot_name name,IN upto_lsn pg_lsn,IN upto_nchangesint, VARIADIC optionstext[] DEFAULT'{}',
422419
OUT lsn pg_lsn, OUT xid xid, OUT datatext)

‎src/backend/commands/Makefile

Lines changed: 1 addition & 2 deletions
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@@ -61,7 +61,6 @@ OBJS = \
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vacuum.o\
6262
vacuumparallel.o\
6363
variable.o\
64-
view.o\
65-
waitlsn.o
64+
view.o
6665

6766
include$(top_srcdir)/src/backend/common.mk

‎src/backend/commands/meson.build

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@@ -50,5 +50,4 @@ backend_sources += files(
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'vacuumparallel.c',
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'variable.c',
5252
'view.c',
53-
'waitlsn.c',
5453
)

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