Remove replication slot advice from MultiXact wraparound hints

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

diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index 356e826ff16d7b189dd660a0a7d01ad028f1a31a..80f938bebbfc0b65f239e6c814559978165ad26d 100644 (file)
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -821,6 +821,12 @@ 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

diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index 5067c2a3e394d56fac6bf4e2665e742c8be6a707..9020f1448c44129239c18608569d5d81131450b6 100644 (file)
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -1260,14 +1260,14 @@ 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.")));
                }
 
                /*
@@ -1291,7 +1291,7 @@ GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
                                                                           oldest_datname,
                                                                           multiWrapLimit - result),
                                                 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",
@@ -1300,7 +1300,7 @@ GetNewMultiXactId(int nmembers, MultiXactOffset *offset)
                                                                           oldest_datoid,
                                                                           multiWrapLimit - result),
                                                 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 */
@@ -2647,7 +2647,7 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid,
                                                                   oldest_datname,
                                                                   multiWrapLimit - curMulti),
                                         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",
@@ -2656,7 +2656,7 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid,
                                                                   oldest_datoid,
                                                                   multiWrapLimit - curMulti),
                                         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.")));
        }
 }
 

diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index c42c8a680d3a6da38a9b1d9f55b0b31f87dfb5cb..b6c4216d428905236ff4da0ef6056ca6683adc75 100644 (file)
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -1155,7 +1155,7 @@ 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