Update autovacuum_freeze_max_age documentation to mention that the

default is low because of pg_clog file removal.

Backpatch to 9.0.X.

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 06ff79a41723d8a3ff60549d8f0c3bc8d42c4f25..d1ad1af6af8dc170d9f8e319120a9b4dfa043c0d 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1,4 +1,4 @@
-
+
 
 
   Server Configuration
@@ -4150,12 +4150,16 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
        
         Specifies the maximum age (in transactions) that a table's
         pg_class.relfrozenxid field can
-        attain before a VACUUM operation is forced to allow removal
-        of old files from the pg_clog subdirectory and prevent
-        transaction ID wraparound within the table.  Note that the system
-        will launch autovacuum processes to prevent wraparound even when
-        autovacuum is otherwise disabled.
-        The default is 200 million transactions.
+        attain before a VACUUM operation is forced
+        to prevent transaction ID wraparound within the table.
+        Note that the system will launch autovacuum processes to
+        prevent wraparound even when autovacuum is otherwise disabled.
+       
+
+       
+        Vacuum also allows removal of old files from the
+        pg_clog subdirectory, which is why the default
+        is a relatively low 200 million transactions.
         This parameter can only be set at server start, but the setting
         can be reduced for individual tables by
         changing storage parameters.