Document that autovacuum_freeze_max_age is used for pg_clog recycling.

We already mentioned xid wraparound.

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d437727d3357d06bb354887e58e331843b6ec049..8e91a744d71f0c285e5876a5e3980898501258b7 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1,4 +1,4 @@
-
+
 
 
   Server Configuration
@@ -4150,7 +4150,8 @@ 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 prevent
+        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.