From: MichaelDBA <MichaelDBA@sqlexec.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: aditya desai <admad123@gmail.com>
Cc: Pgsql Performance <pgsql-performance@lists.postgresql.org>
Subject: Re: ALTER STATEMENT getting blocked
Date: Thu, 19 Jan 2023 16:06:17 -0500
Message-ID: <5687dadc-ffd7-458c-563d-441674fd9b04@sqlexec.com> (raw)
In-Reply-To: <4178687.1674150355@sss.pgh.pa.us>
References: <CAN0SRDFCTuHU6ENsJmhxRtzLF6N4hXPONQsOtoF8ZiwNuSx+bg@mail.gmail.com>
<4178687.1674150355@sss.pgh.pa.us>
Do something like this to get it without being behind other
transactions...You either get in and get your work done or try again
DO language plpgsql $$
BEGIN
FOR get_lock IN 1 .. 100 LOOP
BEGIN
ALTER TABLE mytable <do something>;
EXIT;
END;
END LOOP;
END;
$$;
Tom Lane wrote on 1/19/2023 12:45 PM:
> aditya desai <admad123@gmail.com> writes:
>> We have a Postgres 11.16 DB which is continuously connected to informatica
>> and data gets read from it continuously.
>> When we have to ALTER TABLE.. ADD COLUMN.. it gets blocked by the SELECTs
>> on the table mentioned by process above.
>> Is there any way to ALTER the table concurrently without getting blocked?
>> Any parameter or option? Can someone give a specific command?
> ALTER TABLE requires exclusive lock to do that, so it will queue up
> behind any existing table locks --- but then new lock requests will
> queue up behind its request. So this'd only happen if your existing
> reading transactions don't terminate. Very long-running transactions
> are unfriendly to other transactions for lots of reasons including
> this one; see if you can fix your application to avoid that. Or
> manually cancel the blocking transaction(s) after the ALTER begins
> waiting.
>
> regards, tom lane
>
>
Regards,
Michael Vitale
Michaeldba@sqlexec.com <mailto:michaelvitale@sqlexec.com>
703-600-9343
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To: pgsql-performance@postgresql.org
Cc: MichaelDBA@sqlexec.com, tgl@sss.pgh.pa.us, admad123@gmail.com, pgsql-performance@lists.postgresql.org
Subject: Re: ALTER STATEMENT getting blocked
In-Reply-To: <5687dadc-ffd7-458c-563d-441674fd9b04@sqlexec.com>
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