How to get user name of record lock

[RobNorthcott]

I'm a bit of an SQL server noob, so forgive me if this is a silly question, but I can't find the answer anywhere...

When my app comes up against a lock and has to wait, I've always displayed a "locked by user xxx" message, so it's easy for the user to shout or run over to the offending workstation and sort it out.

However, I can't work out how to do this with Postgres. I can detect the lock OK by trapping the error when trying to "SELECT .... FOR UPDATE NOWAIT", but can't work out how to identify the offending user. I'm sure it should be possible by looking at the system tables (pg_locks etc), but can't work out exactly how to decipher all the links.

Is this a weird thing to want to do? I'm surprised I can't find anything.

Any pointers much appreciated

Rob

 

[RobNorthcott]

Looks like this forum is dead, but just in case anybody comes across this thread...

We actually managed to work something out that does what we're after.

Using the pgrowlocks() function, then cross-referencing those results with pg_stat_activity by pid = procpid allows us to get the user name and IP address.

For example, if you are tring to lock a record for "BOB" in table "customers" with key field "cust_key",

select usename, client_addr from customers, pg_stat_activity, pgrowlocks('customers')
where cust_key = "BOB" and locked_row = ctid and procpid = pids[1]

will give the user name and IP address of the user having the lock on that record.

Rob