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Update autovacuum_freeze_max_age documentation to mention that the 

default is low because of pg_clog file removal.

Backpatch to 9.0.X.
This commit is contained in:
Bruce Momjian 2010-08-24 13:32:25 +00:00
parent 49b27ab551
commit c107c35df3
1 changed files with 11 additions and 7 deletions
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18
doc/src/sgml/config.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.307 2010/08/23 02:43:25 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.308 2010/08/24 13:32:25 momjian Exp $ -->
<chapter Id="runtime-config">
<title>Server Configuration</title>
@ -4150,12 +4150,16 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
<para>
Specifies the maximum age (in transactions) that a table's
<structname>pg_class</>.<structfield>relfrozenxid</> field can
attain before a <command>VACUUM</> operation is forced to allow removal
of old files from the <filename>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 <command>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.
</para>
<para>
Vacuum also allows removal of old files from the
<filename>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.