Reword messages about impending (M)XID exhaustion.

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

1 files changed, 6 insertions, 5 deletions

diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index 66f2c6a02e8..9389eef973d 100644
--- 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>