Re: strange (maybe) behaviour of table lock

Edoardo Panfili <edoardo(at)aspix(dot)it> writes:
> I have a servlet that uses connection pools.
> The servlet do "LOCK table,table2,table3,table4"
> then do some select (I am testing the code, I will put the update in the
> future) an then I close instruction and connection.
> The first 4 executions of the servlet goes well, the 5th hangs.
> Afther that I use "psql" to do the last query (the one that hangs the
> system) of the servlet, also psql hangs.

Look into the pg_locks view to find out what it's blocked on. Note that
LOCK by default gets an ACCESS EXCLUSIVE lock, which means it will be
blocked by *any* pre-existing access, even an open transaction that
merely read the table awhile back. Are you sure you really need such a
strong lock?

regards, tom lane