Re: Never kill -9 postgres client processes on Linux... but why not?

On 04/18/2018 11:53 PM, Mark Kirkwood wrote:
> Hi,
>
>
> On 19/04/18 16:40, Wells Oliver wrote:
>> Had an issue tonight where I had a bunch of stalled queries from a client
>> connection and I just... could... not... kill... them. We disconnected
>> the client machine, turned it off, picked it up, shook it around, yelled
>> at it, and still these idle queries remained in pg_stat_activity.
>>
>> Then I did select pg_cancel_backend(pid) from pg_stat_activity where
>> client_addr = '..' and they just would... not... go.. away.
>>
>> So me being the big smart system administrator guy with shell access, I
>> logged in, and did a kill -9 xxx where xxx was the sme pid from the
>> pg_stat_activity result and... they finally went away!
>>
>> Felt good about myself until I realized, well, so did every other
>> connection, and in fact PG momentarily went into recovery mode.
>>
>> Everything was fine, but a) why is it a bad idea to kill -9 a client PG
>> process, but pg_cancel_backend() is OK-- and b) what to do about stalled
>> PG queries that won't die when you disconnect AND when you
>> pg_cancel_backend() them?
>>
>
> Did you try pg_terminate_backend? I'm guessing that might not have worked
> either...but is worth it trying before belting them with kill -9!

+1 to pg_terminate_backend.  On the rare occasion pg_cancel_backend doesn't
work, I hit the pid with pg_terminate_backend, and that always works.

--
Angular momentum makes the world go 'round.