Hi John,
> Why does your app need 20 connections just to start up? That's a bit of a
> rhetorical question, but needing so many connections to start up seems odd to
> me.
It doesn't. It only needs 1-2 at a time, but it makes 100s of queries
in loops, each time using a connection from the pool and passing it back.
> Are you using the Tomcat pool or another one? If it's Tomcat, I think you
> should use some of the abandoned connection settings described here:
There're a few wrappers around the org.apache.commons.dbcp classes. I
have abandoned connection settings in place.
The code - in fact, the build - remains completely unchanged throughout
my testing of 9.0.68, 9.0.70 - 9.0.79 as it used the same .war file.
Whilst that doesn't eliminate my code from the equation, it looks like
a problem outside my code.
I will happily revise that view if nobody else has run into a similar
problem in the last 8 months - or if they have and found a cause outside Tomcat.
> If your app is reserving connections and not releasing them, they will be
> considered abandoned. With logAbandoned=true, you'll get a stack trace
> showing where the connection was obtained.
With 9.0.68 and 9.0.70 (indeed with most Tomcat versions I've used
since 8.0... ) we have worked hard to ensure that it does release connections
back to the pool appropriately.
These connections are not "abandoned" - a release was attempted.
> Also, you can take thread dumps to see what your threads are doing. If they
> are actually using the connection, you might see a query in flight. Then you
> can ask yourself why they're taking so long.
I know what the SQL is. It's in the log file. The SQL isn't slow, it's
called multiple times for different tables/data during startup but with the
versions of Tomcat with which I am having problems, it only manages 20 calls
before exhausting the pool.
The SQL is run serially, not in parallel.
Thanks,
Tim
----
> Hi,
>
> For various diagnostics, I tried Tomcat 9.0.79 recently on a development
> machine. It didn't solve the problem I was experiencing - that was later
> identified as a problem in IntelliJ with remote deployment and is not why I'm
> mailing.
>
> I tweaked my Tomcat 9.0.79 configuration to start my application manually, as
> IntelliJ refused to deploy remotely.
>
> This lead to it quickly exhausting its connection pool and then hanging*
> before the application could complete its startup activity.
> * Each request for a connection from the pool timed out. The
> log
> shows that all 20 connections were allocated.
>
> I pointed my system back to 9.0.68, and it started up fine.
>
> I tried all versions I could find back from 9.0.78 through 9.0.71 - and ran
> into
> the same connection pool problem as 9.0.79 with every version.
>
> v9.0.70 worked.
> (well, at least didn't exhibit the same problem - the
> application
> completed its startup activity and was operational).
>
> I would therefore conclude that something about the way I'm managing my
> database connection pool is preventing 9.0.71 onward from freeing up the
> connections.
>
> My application uses javax.sql.DataSource with Corretto JDK 11 (11.0.16+8-
> LTS, to be specific).
>
> It struck me as odd as that means that all releases in the last 8 months have
> this problem for my application. Has anyone else, here, run into a similar
> problem?
>
> If a pool size of 20 is just too low, I think I'd need to set mine to a few
> hundred to complete the application startup and I'm not willing to try that
> without further insight.
>
> Thanks,
> Tim
>
> --
> Tim Scott (he/him/his)
> OCLC * Lead Software Engineer / Technical Product Manager
>
>
> cc: IT file
Why does your app need 20 connections just to start up? That's a bit of a
rhetorical question, but needing so many connections to start up seems odd to
me.
Are you using the Tomcat pool or another one? If it's Tomcat, I think you
should use some of the abandoned connection settings described here:
https://tomcat.apache.org/tomcat-9.0-doc/jdbc-pool.html
If your app is reserving connections and not releasing them, they will be
considered abandoned. With logAbandoned=true, you'll get a stack trace showing
where the connection was obtained.
Also, you can take thread dumps to see what your threads are doing. If they
are actually using the connection, you might see a query in flight. Then you
can ask yourself why they're taking so long.
John
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