On Sat, Aug 10, 2013 at 12:30 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Tatsuo Ishii <ishii@postgresql.org> writes:
>> I noticed pg_dump does not exit gracefully when killed.
>> start pg_dump
>> kill pg_dump by ctrl-c
>> ps x
>
>> 27246 ? Ds 96:02 postgres: t-ishii dbt3 [local] COPY
>> 29920 ? S 0:00 sshd: ishii@pts/5
>> 29921 pts/5 Ss 0:00 -bash
>> 30172 ? Ss 0:00 postgres: t-ishii dbt3 [local] LOCK TABLE waiting
>
>> As you can see, after killing pg_dump, a backend process is (LOCK
>> TABLE waiting) left behind. I think this could be easily fixed by
>> adding signal handler to pg_dump so that it catches the signal and
>> issues a query cancel request.
>
> If we think that's a problem (which I'm not convinced of) then pg_dump
> is the wrong place to fix it. Any other client would behave the same
> if it were killed while waiting for some backend query. So the right
> fix would involve figuring out a way for the backend to kill itself
> if the client connection goes away while it's waiting.
This seems to me to be quite a bit like the TCP keepalive issue.
We noticed with Slony that if something ungraceful happens in the
networking layer (the specific thing noticed was someone shutting off
networking, e.g. "/etc/init.d/networking stop" before shutting down
Postgres+Slony), the usual timeouts are really rather excessive, on
the order of a couple hours.
Probably it would be desirable to reduce the timeout period, so that
the server could figure out that clients are incommunicado "reasonably
quickly." It's conceivable that it would be apropos to diminish the
timeout values in postgresql.conf, or at least to recommend that users
consider doing so.
--
When confronted by a difficult problem, solve it by reducing it to the
question, "How would the Lone Ranger handle this?"