apparent deadlock

Hello,

I'm working with Pg 7.4 on CentOS, and I'm seeing an apparent deadlock which
is not resolving itself.

According to the postgres documentation, deadlocks should be detected and
resolved by killing one or more transactions involved.

http://www.postgresql.org/docs/current/static/explicit-locking.html

What I'm seeing is an upgrade of an application running a series of alter
table commands to migrate the db schema, but blocking during the process and
never continuing. I finally had to restart the db to unblock the process.

Does anyone have any suggestions for troubleshooting a potential deadlock like
this? I'm not sure how to query existing locks on tables, for example, which
might tell me where the issue is.

Thank you,
mps
--
Michael P. Soulier <michael_soulier(at)mitel(dot)com>, 613-592-2122 x2522
"Any intelligent fool can make things bigger and more complex... It takes a
touch of genius - and a lot of courage to move in the opposite direction."
--Albert Einstein