Re: Problem with permanent connections from Tomcat

Hi,
An elegant solution to this problem is to instruct the Tomcat
developers
to use conection-pooling datasources. That way their Tomcat server
takes care of the connection pool and terminates idle connections
when they time out. This way Tomcat also tear down its connections
when it's shut down.

I run this setup with Tomcat 5.0.24 and it works great for me.

/John

>>> Tom Arthurs <tom@jobflash.com> 07-02-2005 11:04:16 >>>
Hi, Daniel

I run a similar environment and I've seen this problem a lot.

It's a java code problem -- your developers need to run a profiler to
see where the resource leaks are -- they need to make sure that
everytime they open a connection, they also close it as well -- and
don't forget to to close the statements.  We use borland's optimizeit
which is not free (by a long shot) but it's probably worth the
investment -- you can't promote code to production that is leaking
resources like this.  (Are you using connection pooling on tomcat?)

If they all shutdown their tomcat instances, it should release the
connection, don't know how popular that suggestion would be though.

If you have the berkely version of ps (on solaris I use /usr/ucb/ps
-auxww | grep post) you can see where each of these connections is
coming from and some indication of what it's doing, and you can do a
kill -15 on each one of them -- which is a more graceful recovery.

For a quick and dirty fix -- do pg_ctl stop -m i
That's an immediate shutdown -- though it's still a "dirty" shutdown
and the db must recover on startup, so make sure your backups and
txlogs are good -- *don't* run out of room for the txlogs.

Daniel Rubio wrote:
> Hi all
>
> Our developers are making some kind of DoS on my postgres
installation.
> They use Tomcat to develop in java and they have an instance on every

> computer (only 3).
>
> It seems that tomcat makes permanent connections to the configured
> database, but they have this number limited to 5, and max_connections
in
> postgresql.conf is 40, and no more connections are made to the
database
> because is a development environment.
>
> The number of connections starts increasing and when arrives to 40 (
ps
> -ef | grep postm | wc -l ) the server doesn't accept more connections

> but it seems that neither finish these that are open, and no one can

> acces to the database (here is the DoS I say).
>
> Here is what the log says
>
> 2005-02-07 10:13:26 LOG:  connection received: host=127.0.0.1
port=55834
> 2005-02-07 10:13:26 LOG:  connection authorized: user=test
database=test
> 2005-02-07 10:13:26 FATAL:  connection limit exceeded for
non-superusers
>
> I try to stop the postmaster with pg_ctl but it says that postmaster

> doesn't stops and I have to make kill -9 for the processes to stop
:(
>
> What could I make to solve this?
>
> I've tried with:
>
> statement_timeout = 100000
>
> but nothing happens ... :(
>

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