Re: ALTER STATEMENT getting blocked

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(at)gmail(dot)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(at)sqlexec(dot)com <mailto:michaelvitale(at)sqlexec(dot)com>

703-600-9343