<para>

The sole disadvantage of increasing <varname>autovacuum_freeze_max_age</>

(and <varname>vacuum_freeze_table_age</> along with it)

is that the <filename>pg_xact</> subdirectory of the database cluster

will take more space, because it must store the commit status of all

transactions back to the <varname>autovacuum_freeze_max_age</> horizon.

The commit status uses two bits per transaction, so if

<varname>autovacuum_freeze_max_age</> is set to its maximum allowed

value of two billion, <filename>pg_xact</> can be expected to

grow to about half a gigabyte. If this is trivial compared to your

total database size, setting <varname>autovacuum_freeze_max_age</> to

its maximum allowed value is recommended. Otherwise, set it depending

on what you are willing to allow for <filename>pg_xact</> storage.

(The default, 200 million transactions, translates to about 50MB of

<filename>pg_xact</> storage.)

(and <varname>vacuum_freeze_table_age</> along with it) is that

the <filename>pg_xact</> and <filename>pg_commit_ts</filename>

subdirectories of the database cluster will take more space, because it

must store the commit status and (if <varname>track_commit_timestamp</> is

enabled) timestamp of all transactions back to

the <varname>autovacuum_freeze_max_age</> horizon. The commit status uses

two bits per transaction, so if

<varname>autovacuum_freeze_max_age</> is set to its maximum allowed value

of two billion, <filename>pg_xact</> can be expected to grow to about half

a gigabyte and <filename>pg_commit_ts</filename> to about 20GB. If this

is trivial compared to your total database size,

setting <varname>autovacuum_freeze_max_age</> to its maximum allowed value

is recommended. Otherwise, set it depending on what you are willing to

allow for <filename>pg_xact</> and <filename>pg_commit_ts</> storage.

(The default, 200 million transactions, translates to about 50MB

of <filename>pg_xact</> storage and about 2GB of <filename>pg_commit_ts</>

storage.)

</para>

<para>