Re: Adding some error context for lock wait failures

On Thu, Jul 10, 2025 at 10:36 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> I noted a complaint [1] about how hard it is to debug unforeseen
> lock-timeout failures: we give no details about what we were
> waiting for.  It's not hard to improve that situation, at least
> to the extent of printing numeric locktag details similar to what
> you get in deadlock reports.  (It'd be nice to give object names,
> but just as with deadlocks, incurring any additional lock
> acquisitions here seems too scary.)  The attached patch will
> produce reports like
>
> regression=# begin;
> BEGIN
> regression=*# lock table tenk1;
> ^CCancel request sent
> ERROR:  canceling statement due to user request
> CONTEXT:  waiting for AccessExclusiveLock on relation 77382 of database 77348
> regression=!# abort;
> ROLLBACK
> regression=#  set lock_timeout TO '1s';
> SET
> regression=# begin;
> BEGIN
> regression=*# lock table tenk1;
> ERROR:  canceling statement due to lock timeout
> CONTEXT:  waiting for AccessExclusiveLock on relation 77382 of database 77348
>
> and then the user can manually look up the object's identity.
>

This seems to be quite useful to me, initially I thought if we can
print the relation and database name then this could be even better
but it might be a bad idea to fetch the object name while we are in
error callback.  And anyway deadlock error is also reported in the
same format so this makes sense.

--
Regards,
Dilip Kumar
Google