Re: locking issue on simple selects?

Tobias Brox wrote:
> I thought so, we have a logging script that logs the content of
> the pg_locks table, it didn't log anything interesting but it may be a
> problem with the script itself.  It does an inner join on
> pg_locks.relation = pg_class.oid but when I check now this join seems
> to remove most of the rows in the pg_locks table.

Some of the waits you might be running into will be things waiting on
another transaction holding a lock to finish, which are probably wiped
out by this approach.  There are some useful examples of lock views on
the wiki:

http://wiki.postgresql.org/wiki/Lock_Monitoring
http://wiki.postgresql.org/wiki/Lock_dependency_information
http://wiki.postgresql.org/wiki/Find_Locks

And the idea you have of coverting the pg_class one to an outer join
will help.

The other thing you should try is toggling on log_lock_waits and
possibly reducing deadlock_timeout.  This will put a lot of the
information you're trying to collect right into the logs.

--
Greg Smith, 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
PostgreSQL Training, Services and Support  www.2ndQuadrant.us
Author, "PostgreSQL 9.0 High Performance"    Pre-ordering at:
https://www.packtpub.com/postgresql-9-0-high-performance/book