Re: Cannot terminate backend

Afraid so. You can wait longer, I guess. You may have found two bugs… the lack of an interrupt in the dbscan loop, which I’m working on now. And maybe an infinite looping case? In which case if you want a fix on that, you’ll have to share your data and query.

P.

> On Mar 31, 2023, at 7:41 AM, Arnaud Lesauvage <arnaud(dot)listes(at)codata(dot)eu> wrote:
>
>> On Fri, 2023-03-31 at 13:46 +0000, Arnaud Lesauvage wrote:
>>> I have a long running query that I seem unable to either cancel or
>> terminate.
>>> What could be the reason for this, and what is the bet way to terminate
>> this kind of query ?
>>>
>>> The query is a CTE using postgis ST_ClusterDBSCAN function. The CTE
>> returns approximately 150k rows.
>>> The SQL is as follows :
>>>
>>> EXPLAIN ANALYZE
>>> WITH subq AS (
>>> SELECT id, geom, ST_ClusterDBSCAN(geom, eps := 1000, minpoints
>>> := 1) OVER() AS cluster_id
>>> FROM mytable
>>> )
>>> SELECT cluster_id, count(id), ST_Collect(geom) FROM subq GROUP BY
>>> cluster_id;
>>>
>>> pg_stat_activity show no wait event.
>>> pg_cancel_backend(mypid) returns true but the state does not change in
>> pg_stat_activity.
>>> pg_terminate_backend(mypid) yields the same result (as superuser)
>>> Pg_stat_activity show no wait_event.
>>>
>>> SELECT version();
>>> PostgreSQL 14.5 (Ubuntu 14.5-1.pgdg20.04+1) on x86_64-pc-linux-gnu,
>>> compiled by gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0, 64-bit
>>
>> The most likely explanation is that one of the PostGIS functions runs for a
>> long time without checking CHECK_FOR_INTERRUPTS().
>> That would be a PostGIS bug. Try to construct a reproducible test case that
>> you can share!
>>
>> Perhaps this trick can help:
>> https://www.cybertec-postgresql.com/en/cancel-hanging-postgresql-
>> query/
>
>
> Thanks Laurenz
> Unfortunately, I don't have a shell access to the server, so I guess I'll have to ask to sysadmin to kill -9 ?
>
> Regards
> Arnaud