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Remove replication slot advice from MultiXact wraparound hints

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Previously, MultiXactId wraparound hints suggested dropping stale
replication slots. While that advice is appropriate for transaction ID
wraparound, where replication slots can hold back XID horizons,
it was misleading for MultiXactId wraparound. Following it could lead
users to drop replication slots unnecessarily without helping resolve
the MultiXactId wraparound condition.

MultiXact cleanup is not directly delayed by replication slots.
Instead, it depends on whether old MultiXactIds can still be seen
as live by running transactions.

This commit removes the replication slot advice from MultiXactId
wraparound hints, and documents that stale replication slots are
normally not relevant to resolving MultiXactId wraparound problems.

Backpatch to all supported branches.

BUG #18876
Reported-by: Haruka Takatsuka <harukat@sraoss.co.jp>
Author: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/18876-0d0b53bad5a1f4c1@postgresql.org
Backpatch-through: 14
This commit is contained in:
Fujii Masao 2026-07-03 11:16:34 +09:00
parent 89f5f860cc
commit 4ebbf00188
3 changed files with 13 additions and 7 deletions
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6
doc/src/sgml/maintenance.sgml
View file

@ -869,6 +869,12 @@ HINT: Execute a database-wide VACUUM in that database.
<simpara>Running transactions and prepared transactions can be ignored if there
is no chance that they might appear in a multixact.</simpara>
</listitem>
<listitem>
<simpara>Unlike transaction ID wraparound, replication slots do not
directly hold back multixact cleanup. Dropping stale replication
slots is therefore not usually relevant to resolving multixact ID
wraparound problems.</simpara>
</listitem>
<listitem>
<simpara>MXID information is not directly visible in system views such as
<literal>pg_stat_activity</literal>; however, looking for old XIDs is still a good

12
src/backend/access/transam/multixact.c
View file

@ -1040,14 +1040,14 @@ GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
errmsg("database is not accepting commands that assign new MultiXactIds to avoid wraparound data loss in database \"%s\"",
oldest_datname),
errhint("Execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
"You might also need to commit or roll back old prepared transactions.")));
else
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("database is not accepting commands that assign new MultiXactIds to avoid wraparound data loss in database with OID %u",
oldest_datoid),
errhint("Execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
"You might also need to commit or roll back old prepared transactions.")));
}
/*
@ -1073,7 +1073,7 @@ GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
errdetail("Approximately %.2f%% of MultiXactIds are available for use.",
(double) (multiWrapLimit - result) / (MaxMultiXactId / 2) * 100),
errhint("Execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
"You might also need to commit or roll back old prepared transactions.")));
else
ereport(WARNING,
(errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
@ -1084,7 +1084,7 @@ GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
errdetail("Approximately %.2f%% of MultiXactIds are available for use.",
(double) (multiWrapLimit - result) / (MaxMultiXactId / 2) * 100),
errhint("Execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
"You might also need to commit or roll back old prepared transactions.")));
}
/* Re-acquire lock and start over */
@ -2211,7 +2211,7 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid)
errdetail("Approximately %.2f%% of MultiXactIds are available for use.",
(double) (multiWrapLimit - curMulti) / (MaxMultiXactId / 2) * 100),
errhint("To avoid MultiXactId assignment failures, execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
"You might also need to commit or roll back old prepared transactions.")));
else
ereport(WARNING,
(errmsg_plural("database with OID %u must be vacuumed before %u more MultiXactId is used",
@ -2222,7 +2222,7 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid)
errdetail("Approximately %.2f%% of MultiXactIds are available for use.",
(double) (multiWrapLimit - curMulti) / (MaxMultiXactId / 2) * 100),
errhint("To avoid MultiXactId assignment failures, execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
"You might also need to commit or roll back old prepared transactions.")));
}
}

2
src/backend/commands/vacuum.c
View file

@ -1177,7 +1177,7 @@ vacuum_get_cutoffs(Relation rel, const VacuumParams *params,
ereport(WARNING,
(errmsg("cutoff for freezing multixacts is far in the past"),
errhint("Close open transactions soon to avoid wraparound problems.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
"You might also need to commit or roll back old prepared transactions.")));
/*
* Determine the minimum freeze age to use: as specified by the caller, or