Reword messages about impending (M)XID exhaustion.

robertmhaas · robertmhaas · commit 2406c4e34ccc · 2023-10-17T10:34:21.000-04:00
First, we shouldn't recommend switching to single-user mode, because that's terrible advice. Especially on newer versions where VACUUM will enter emergency mode when nearing (M)XID exhaustion, it's perfectly fine to just VACUUM in multi-user mode. Doing it that way is less disruptive and avoids disabling the safeguards that prevent actual wraparound, so recommend that instead. Second, be more precise about what is going to happen (when we're nearing the limits) or what is happening (when we actually hit them). The database doesn't shut down, nor does it refuse all commands. It refuses commands that assign whichever of XIDs and MXIDs are nearly exhausted. No back-patch. The existing hint that advises going to single-user mode is sufficiently awful advice that removing it or changing it might be justifiable even though we normally avoid changing user-facing messages in back-branches, but I (rhaas) felt that it was better to be more conservative and limit this fix to master only. Aside from the usual risk of breaking translations, people might be used to the existing message, or even have monitoring scripts that look for it. Alexander Alekseev, John Naylor, Robert Haas, reviewed at various times by Peter Geoghegan, Hannu Krosing, and Andres Freund. Discussion: http://postgr.es/m/CA+TgmoZBg95FiR9wVQPAXpGPRkacSt2okVge+PKPPFppN7sfnQ@mail.gmail.com
diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
@@ -656,7 +656,7 @@ SELECT datname, age(datfrozenxid) FROM pg_database;
 
 <programlisting>
 WARNING:  database "mydb" must be vacuumed within 39985967 transactions
-HINT:  To avoid a database shutdown, execute a database-wide VACUUM in that database.
+HINT:  To avoid XID assignment failures, execute a database-wide VACUUM in that database.
 </programlisting>
 
     (A manual <command>VACUUM</command> should fix the problem, as suggested by the
@@ -667,16 +667,17 @@ HINT:  To avoid a database shutdown, execute a database-wide VACUUM in that data
     there are fewer than three million transactions left until wraparound:
 
 <programlisting>
-ERROR:  database is not accepting commands to avoid wraparound data loss in database "mydb"
-HINT:  Stop the postmaster and vacuum that database in single-user mode.
+ERROR:  database is not accepting commands that assign new XIDs to avoid wraparound data loss in database "mydb"
+HINT:  Execute a database-wide VACUUM in that database.
 </programlisting>
 
     In this condition any transactions already in progress can continue,
     but only read-only transactions can be started. Operations that
     modify database records or truncate relations will fail.
     The <command>VACUUM</command> command can still be run normally.
-    Contrary to what the hint states, it is not necessary or desirable to stop the
-    postmaster or enter single user-mode in order to restore normal operation.
+    Note that, contrary to what was sometimes recommended in earlier releases,
+    it is not necessary or desirable to stop the postmaster or enter single
+    user-mode in order to restore normal operation.
     Instead, follow these steps:
 
     <orderedlist>
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
@@ -2335,7 +2335,7 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid,
 								   multiWrapLimit - curMulti,
 								   oldest_datname,
 								   multiWrapLimit - curMulti),
-					 errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
+					 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.")));
 		else
 			ereport(WARNING,
@@ -2344,7 +2344,7 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid,
 								   multiWrapLimit - curMulti,
 								   oldest_datoid,
 								   multiWrapLimit - curMulti),
-					 errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
+					 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.")));
 	}
 }
diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c
@@ -126,16 +126,16 @@ GetNewTransactionId(bool isSubXact)
 			if (oldest_datname)
 				ereport(ERROR,
 						(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
-						 errmsg("database is not accepting commands to avoid wraparound data loss in database \"%s\"",
+						 errmsg("database is not accepting commands that assign new XIDs to avoid wraparound data loss in database \"%s\"",
 								oldest_datname),
-						 errhint("Stop the postmaster and vacuum that database in single-user mode.\n"
+						 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.")));
 			else
 				ereport(ERROR,
 						(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
-						 errmsg("database is not accepting commands to avoid wraparound data loss in database with OID %u",
+						 errmsg("database is not accepting commands that assign new XIDs to avoid wraparound data loss in database with OID %u",
 								oldest_datoid),
-						 errhint("Stop the postmaster and vacuum that database in single-user mode.\n"
+						 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.")));
 		}
 		else if (TransactionIdFollowsOrEquals(xid, xidWarnLimit))
@@ -148,14 +148,14 @@ GetNewTransactionId(bool isSubXact)
 						(errmsg("database \"%s\" must be vacuumed within %u transactions",
 								oldest_datname,
 								xidWrapLimit - xid),
-						 errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
+						 errhint("To avoid XID 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.")));
 			else
 				ereport(WARNING,
 						(errmsg("database with OID %u must be vacuumed within %u transactions",
 								oldest_datoid,
 								xidWrapLimit - xid),
-						 errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
+						 errhint("To avoid XID 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.")));
 		}
 
@@ -463,14 +463,14 @@ SetTransactionIdLimit(TransactionId oldest_datfrozenxid, Oid oldest_datoid)
 					(errmsg("database \"%s\" must be vacuumed within %u transactions",
 							oldest_datname,
 							xidWrapLimit - curXid),
-					 errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
+					 errhint("To avoid XID 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.")));
 		else
 			ereport(WARNING,
 					(errmsg("database with OID %u must be vacuumed within %u transactions",
 							oldest_datoid,
 							xidWrapLimit - curXid),
-					 errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
+					 errhint("To avoid XID 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.")));
 	}
 }
