From f73cf585727aec1fd926fdf2b729935bf6c9c6e2 Mon Sep 17 00:00:00 2001 From: Amit Kapila Date: Tue, 17 Sep 2019 11:20:00 +0530 Subject: [PATCH] Doc: document autovacuum interruption. It's important users be able to know (without looking at the source code) that running DDL or DDL-like commands frequently can interrupt autovacuum enough that it will effectively never run, resulting in lots of pain with dead tuples. Reported-by: James Coleman Author: James Coleman Reviewed-by: Amit Kapila Backpatch-through: 9.4 Discussion: https://postgr.es/m/CAAaqYe-XYyNwML1=f=gnd0qWg46PnvD=BDrCZ5-L94B887XVxQ@mail.gmail.com --- doc/src/sgml/maintenance.sgml | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml index d95c218..6957e21 100644 --- a/doc/src/sgml/maintenance.sgml +++ b/doc/src/sgml/maintenance.sgml @@ -825,6 +825,26 @@ analyze threshold = analyze base threshold + analyze scale factor * number of tu autovacuum_vacuum_cost_limit storage parameters have been set are not considered in the balancing algorithm. + + + Autovacuum workers generally don't block other commands. If a process + attempts to acquire a lock that conficts with the + SHARE UPDATE EXCLUSIVE lock held by autovacuum, lock + acquisition will interrupt the autovacuum. For conflicting lock modes, + see . However, if the autovacuum + is running to prevent transaction ID wraparound (i.e., the autovacuum query + name in the pg_stat_activity view ends with + (to prevent wraparound)), the autovacuum is not + automatically interrupted. + + + + + Regularly running commands that acquire locks conflicting with a + SHARE UPDATE EXCLUSIVE lock (e.g., ANALYZE) can + effectively prevent autovacuums from ever completing. + + -- 1.8.3.1