VACUUM performs an aggressive scan if the table's pg_class.relfrozenxid field has reached the age specified by this setting. An aggressive scan differs from a regular VACUUM in that it visits every page that might contain unfrozen XIDs or MXIDs, not just those that might contain dead tuples. The default is 150 million transactions. Although users can set this value anywhere from zero to two billion, VACUUM will silently limit the effective value to 95% of autovacuum_freeze_max_age, so that a periodic manual VACUUM has a chance to run before an anti-wraparound autovacuum is launched for the table. For more information see vacuum-for-wraparound.
- Overhauling "Routine Vacuuming" docs, particularly its handling of freezing
- Re: New strategies for freezing, advancing relfrozenxid early
- Re: Temporary tables versus wraparound... again
- Re: Option to not use ringbuffer in VACUUM, using it in failsafe mode
- Re: Overhauling "Routine Vacuuming" docs, particularly its handling of freezing