Thread:

On Tue, 2021-03-30 at 12:36 +0530, Devendra Yadav wrote:
> Hope everything is well with you. 

Thanks, yes.  I hope you are fine too.

> We are running on PostgreSQL v 12.1 , Redhat 7.8.
> We are running a query  - ALTER TABLE mytable ADD COLUMN deposited DOUBLE PRECISION;
> 
> This query is blocked by pid 0. It's not a postgres PID and won't allow to terminate from postgres. 
> What would  be the way forward to troubleshoot this?

That is probably a stale prepared transaction.

Look into "pg_prepared_xacts" for any prepared transactions and use

  ROLLBACK PREPARED 'name';

to remove stale entries.

When using prepared transactions, you must use a transaction manager
that does these things for you.  Also, you should monitor prepared
transactions.

Yours,
Laurenz Albe
-- 
Cybertec | https://www.cybertec-postgresql.com

Devendra Yadav <devendra.857@gmail.com> writes:
> We are running on PostgreSQL v 12.1 , Redhat 7.8.
> We are running a query  - ALTER TABLE mytable ADD COLUMN deposited DOUBLE
> PRECISION;
> This query is blocked by pid 0. It's not a postgres PID and won't allow to
> terminate from postgres.

It would be better if you showed the evidence that makes you think this,
as it's fairly likely that the true problem is somewhere else than
you think.

At a guess, however, a pg_locks display that suggests a lock is held
by "pid 0" might be trying to represent a lock held by a prepared-but-
uncommitted transaction.  Try looking into the pg_prepared_xacts view.

            regards, tom lane