diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/maintenance.sgml | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml index 84fba9dcb10..2e09fee5aeb 100644 --- a/doc/src/sgml/maintenance.sgml +++ b/doc/src/sgml/maintenance.sgml @@ -586,11 +586,11 @@ statistics in the system tables <structname>pg_class</structname> and <structname>pg_database</structname>. In particular, the <structfield>relfrozenxid</structfield> column of a table's - <structname>pg_class</structname> row contains the freeze cutoff XID that was used - by the last aggressive <command>VACUUM</command> for that table. All rows - inserted by transactions with XIDs older than this cutoff XID are - guaranteed to have been frozen. Similarly, - the <structfield>datfrozenxid</structfield> column of a database's + <structname>pg_class</structname> row contains the oldest remaining unfrozen + XID at the end of the most recent <command>VACUUM</command> that successfully + advanced <structfield>relfrozenxid</structfield> (typically the most recent + aggressive VACUUM). Similarly, the + <structfield>datfrozenxid</structfield> column of a database's <structname>pg_database</structname> row is a lower bound on the unfrozen XIDs appearing in that database — it is just the minimum of the per-table <structfield>relfrozenxid</structfield> values within the database. @@ -638,7 +638,11 @@ SELECT datname, age(datfrozenxid) FROM pg_database; set <literal>age(relfrozenxid)</literal> to a value just a little more than the <varname>vacuum_freeze_min_age</varname> setting that was used (more by the number of transactions started since the - <command>VACUUM</command> started). If no <structfield>relfrozenxid</structfield>-advancing + <command>VACUUM</command> started). <command>VACUUM</command> + will set <structfield>relfrozenxid</structfield> to the oldest XID + that remains in the table, so it's possible that the final value + will be much more recent than strictly required. + If no <structfield>relfrozenxid</structfield>-advancing <command>VACUUM</command> is issued on the table until <varname>autovacuum_freeze_max_age</varname> is reached, an autovacuum will soon be forced for the table. |