Revert "Reject concurrent sequence refreshes".

This reverts commit f38afa4abb04e85530c94b88daf11c089375daca.

That commit fixed a race that could leave stale sequence values on the
subscriber after 'ALTER SUBSCRIPTION ... REFRESH SEQUENCES'. It did so by
raising an ERROR during 'ALTER SUBSCRIPTION ... REFRESH SEQUENCES'
whenever a sequence synchronization worker was already running for the
subscription.

That approach caused intermittent buildfarm failures, because the existing
tests did not ensure the sequencesync worker had stopped before executing
'ALTER SUBSCRIPTION ... REFRESH SEQUENCES'. While discussing how to fix
the tests, we concluded that blocking the command while a sequencesync
worker is running is inconvenient for users. So we will fix the original
race differently in a follow-up commit.

Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Author: Amit Kapila <amit.kapila16@gmail.com>
Backpatch-through: 19
Discussion: https://postgr.es/m/3614163.1784163070@sss.pgh.pa.us
Discussion: https://postgr.es/m/20260710045217.f0.noahmisch@microsoft.com

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 94b163cccc97d698de4e56a2480beb73be21151b..ee06a726f420d3f14d1df853e14fece6b0022f18 100644 (file)
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1304,33 +1304,6 @@ AlterSubscription_refresh_seq(Subscription *sub)
        WalReceiverConn *wrconn;
        bool            must_use_password;
 
-       /*
-        * Disallow a concurrent REFRESH SEQUENCES while a sequence sync worker
-        * for this subscription is still running. This avoids a race where the
-        * publisher's sequence advances after the current worker has fetched its
-        * value but before it marks the sequence READY. A user may then issue
-        * another REFRESH SEQUENCES to synchronize the updated value. Since the
-        * affected sequences are already in the INIT state, the running worker
-        * has no indication that a new synchronization has been requested. It
-        * would then apply the stale value it already fetched and mark the
-        * sequence READY, causing the new synchronization request to be lost and
-        * preventing the updated publisher values from being synchronized.
-        */
-       LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-       if (logicalrep_worker_find(WORKERTYPE_SEQUENCESYNC, sub->oid, InvalidOid,
-                                                          true))
-       {
-               LWLockRelease(LogicalRepWorkerLock);
-               ereport(ERROR,
-                               errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-               /* translator: %s is an SQL ALTER command */
-                               errmsg("cannot execute %s while a sequence synchronization worker is running",
-                                          "ALTER SUBSCRIPTION ... REFRESH SEQUENCES"),
-                               errhint("Try again after the current synchronization completes."));
-       }
-
-       LWLockRelease(LogicalRepWorkerLock);
-
        /* Load the library providing us libpq calls. */
        load_file("libpqwalreceiver", false);
 

diff --git a/src/test/subscription/t/036_sequences.pl b/src/test/subscription/t/036_sequences.pl
index b3b3b20f82be547d8905fa3e12f68416c06ee3d6..77ac9386cd86ebdf85e7c57adcc98cf4ffbd68c2 100644 (file)
--- a/src/test/subscription/t/036_sequences.pl
+++ b/src/test/subscription/t/036_sequences.pl
@@ -286,10 +286,6 @@ $node_publisher->safe_psql(
        CREATE SEQUENCE regress_s4 START 10 INCREMENT 2;
 ));
 
-# Wait for the missing sequence added to be synced
-$node_subscriber->poll_query_until('postgres', $synced_query)
-  or die "Timed out while waiting for subscriber to synchronize data";
-
 ##########
 # Ensure that insufficient privileges on the publisher for a sequence
 # are reported correctly as a permission issue, not as a missing sequence.