Replace hardcoded 200000000 with autovacuum_freeze_max_age

Parts of the code used autovacuum_freeze_max_age to determine whether
anti-multixact-wraparound vacuums are necessary, while others used a
hardcoded 200000000 value.  This leads to problems when
autovacuum_freeze_max_age is set to a non-default value.  Use the latter
everywhere.

Backpatch to 9.3, where vacuuming of multixacts was introduced.

Andres Freund

diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index e3f5cbc0cd9ca2a20ffe8b1332a249d877aaafcb..de0193aaf6453d2b74e275c6cc207f262389e29d 100644 (file)
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -74,6 +74,7 @@
 #include "funcapi.h"
 #include "miscadmin.h"
 #include "pg_trace.h"
+#include "postmaster/autovacuum.h"
 #include "storage/lmgr.h"
 #include "storage/pmsignal.h"
 #include "storage/procarray.h"
@@ -1958,6 +1959,10 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid)
        /*
         * We'll refuse to continue assigning MultiXactIds once we get within 100
         * multi of data loss.
+        *
+        * Note: This differs from the magic number used in
+        * SetTransactionIdLimit() since vacuum itself will never generate new
+        * multis.
         */
        multiStopLimit = multiWrapLimit - 100;
        if (multiStopLimit < FirstMultiXactId)
@@ -1979,9 +1984,12 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid)
 
        /*
         * We'll start trying to force autovacuums when oldest_datminmxid gets to
-        * be more than 200 million transactions old.
+        * be more than autovacuum_freeze_max_age mxids old.
+        *
+        * It's a bit ugly to just reuse limits for xids that way, but it doesn't
+        * seem worth adding separate GUCs for that purpose.
         */
-       multiVacLimit = oldest_datminmxid + 200000000;
+       multiVacLimit = oldest_datminmxid + autovacuum_freeze_max_age;
        if (multiVacLimit < FirstMultiXactId)
                multiVacLimit += FirstMultiXactId;