Add note about diskspace usage of pg_commit_ts

Author: Thomas Munro

diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index fe1e0ed2b3da93e2ccb7d3975b900c0fd30b24df..616aece6c0e2aaeea6cde7c454372db49a8262e0 100644 (file)
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -526,19 +526,23 @@
 
    
     The sole disadvantage of increasing autovacuum_freeze_max_age
-    (and vacuum_freeze_table_age along with it)
-    is that the pg_xact subdirectory of the database cluster
-    will take more space, because it must store the commit status of all
-    transactions back to the autovacuum_freeze_max_age horizon.
-    The commit status uses two bits per transaction, so if
-    autovacuum_freeze_max_age is set to its maximum allowed
-    value of two billion, pg_xact can be expected to
-    grow to about half a gigabyte.  If this is trivial compared to your
-    total database size, setting autovacuum_freeze_max_age to
-    its maximum allowed value is recommended.  Otherwise, set it depending
-    on what you are willing to allow for pg_xact storage.
-    (The default, 200 million transactions, translates to about 50MB of
-    pg_xact storage.)
+    (and vacuum_freeze_table_age along with it) is that
+    the pg_xact and pg_commit_ts
+    subdirectories of the database cluster will take more space, because it
+    must store the commit status and (if track_commit_timestamp is
+    enabled) timestamp of all transactions back to
+    the autovacuum_freeze_max_age horizon.  The commit status uses
+    two bits per transaction, so if
+    autovacuum_freeze_max_age is set to its maximum allowed value
+    of two billion, pg_xact can be expected to grow to about half
+    a gigabyte and pg_commit_ts to about 20GB.  If this
+    is trivial compared to your total database size,
+    setting autovacuum_freeze_max_age to its maximum allowed value
+    is recommended.  Otherwise, set it depending on what you are willing to
+    allow for pg_xact and pg_commit_ts storage.
+    (The default, 200 million transactions, translates to about 50MB
+    of pg_xact storage and about 2GB of pg_commit_ts
+    storage.)