Increase threshold for multixact member emergency autovac to 50%. Analysis by Noah Misch shows that the 25% threshold set by commit 53bb309d2d5a9432d2602c93ed18e58bd2924e15 is lower than any other, similar autovac threshold. While we don't know exactly what value will be optimal for all users, it is better to err a little on the high side than on the low side. A higher value increases the risk that users might exhaust the available space and start seeing errors before autovacuum can clean things up sufficiently, but a user who hits that problem can compensate for it by reducing autovacuum_multixact_freeze_max_age to a value dependent on their average multixact size. On the flip side, if the emergency cap imposed by that patch kicks in too early, the user will experience excessive wraparound scanning and will be unable to mitigate that problem by configuration. The new value will hopefully reduce the risk of such bad experiences while still providing enough headroom to avoid multixact member exhaustion for most users.
Along the way, adjust the documentation to reflect the effects of commit 04e6d3b877e060d8445eb653b7ea26b1ee5cec6b, which taught autovacuum to run for multixact wraparound even when autovacuum is configured off. Branch ------ REL9_4_STABLE Details ------- http://git.postgresql.org/pg/commitdiff/ea70595a3b0ff58bbd9a613fb9458ff6583cbb12 Modified Files -------------- doc/src/sgml/maintenance.sgml | 7 ++++--- src/backend/access/transam/multixact.c | 2 +- 2 files changed, 5 insertions(+), 4 deletions(-) -- Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers
