On 03/12/2014 12:03 PM, Andres Freund wrote: > Hi, > > On 2014-03-12 12:00:25 -0700, Josh Berkus wrote: >> I was just reading Michael's explanation of replication slots >> (http://michael.otacoo.com/postgresql-2/postgres-9-4-feature-highlight-replication-slots/) >> and realized there was something which had completely escaped me in the >> pre-commit discussion: >> >> select pg_drop_replication_slot('slot_1'); >> ERROR: 55006: replication slot "slot_1" is already active >> LOCATION: ReplicationSlotAcquire, slot.c:339 >> >> What defines an "active" slot? > > One with a connected walsender.
In a world of network proxies, a walsender could be "connected" for hours after the replica has ceased to exist. Fortunately, wal_sender_timeout is changeable on a reload. We check for actual standby feedback for the timeout, yes? > >> It seems like there's no way for a DBA to drop slots from the master if >> it's rapidly running out of disk WAL space without doing a restart, and >> there's no way to drop the slot for a replica which the DBA knows is >> permanently offline but was connected earlier. Am I missing something? > > It's sufficient to terminate the walsender and then drop the slot. That > seems ok for now? We have no safe way to terminate the walsender that I know of; pg_terminate_backend() doesn't include walsenders last I checked. So the procedure for this would be: 1) set wal_sender_timeout to some low value (1); 2) reload 3) call pg_drop_replication_slot('slotname') Clumsy, but it will do for a first pass; we can make it better (for example, by adding a "force" boolean to pg_drop_replication_slot) in 9.5. -- Josh Berkus PostgreSQL Experts Inc. http://pgexperts.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers