Re: Replication slots and footguns

On Wed, Mar 12, 2014 at 3:03 PM, Andres Freund <andres@2ndquadrant.com> 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.
>
>> 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?

Urgh.  That error message looks susceptible to improvement.  How about:

replication slot "%s" cannot be dropped because it is currently in use

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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