Play! not shutting down H2 correctly

Question

I'm using Play to write a webapp which is deployed in Tomcat. Because the app won't be processing very much data I'm using the default H2 database with Hibernate. When I want to deploy a new version of the app, I shut down tomcat, wipe the old webapp and WAR, add my new WAR, and start back up.

This worked until a few days ago, when I added the database component. Now, I am often unable to redeploy the app. When I delete the old directory, it is automatically regenerated with this structure:

$ ls -laR myapp/
myapp/:
total 24
drwxr-xr-x  3 root root 4096 Aug 24 17:20 .
drwxr-xr-x 13 root root 4096 Aug 24 17:20 ..
drwxr-xr-x  3 root root 4096 Aug 24 17:20 WEB-INF

myapp/WEB-INF:
total 24
drwxr-xr-x 3 root root 4096 Aug 24 17:20 .
drwxr-xr-x 3 root root 4096 Aug 24 17:20 ..
drwxr-xr-x 3 root root 4096 Aug 24 17:20 application

myapp/WEB-INF/application:
total 24
drwxr-xr-x 3 root root 4096 Aug 24 17:20 .
drwxr-xr-x 3 root root 4096 Aug 24 17:20 ..
drwxr-xr-x 3 root root 4096 Aug 24 17:20 db

myapp/WEB-INF/application/db:
total 24
drwxr-xr-x 3 root root 4096 Aug 24 17:20 .
drwxr-xr-x 3 root root 4096 Aug 24 17:20 ..
drwxr-xr-x 2 root root 4096 Aug 24 17:20 h2

myapp/WEB-INF/application/db/h2:
total 24
drwxr-xr-x 2 root root 4096 Aug 24 17:20 .
drwxr-xr-x 3 root root 4096 Aug 24 17:20 ..
-rw-r--r-- 1 root root  100 Aug 24 17:20 play.lock.db

The same happens when the WAR unzips.

I recently noticed a message whiz by in the catalina.out log complaining about my app not shutting down a process called something like "H2 File Lock Watchdog". Based on a brief search of the H2 docs, I think that process is what's interfering with my app.

EDIT

Here's the complaining line in the log file:

SEVERE: The web application [/myapp] appears to have started a thread named [H2 File Lock Watchdog /var/lib/apache-tomcat-6.0.32/webapps/myapp/WEB-INF/application/db/h2/play.lock.db] but has failed to stop it. This is very likely to create a memory leak.

So, how do I kill this process? I can't restart the machine because it's not mine, and I can't find the watchdog with top or ps. I'd prefer a way for Play to shut it down automagically, but I'm not above building it into my deployment script.

Thanks a million if you've read this far!

Answer 1

I shut down tomcat

Are you sure you have shut down tomcat completely? Because the H2 database is sill running. If you shut down the tomcat process, the database is also stopped (because H2 is running within the tomcat process). Except if you run the database in a different process.

Or did you just shut down the web application within tomcat? If that is the case, then at least one database connection was not closed, so that the database keeps running (and creates this .lock.db file).

Now, I don't know the play framework, and can't say how to ensure all database connections are closed.

One way to force the database to close is to run the SQL statement SHUTDOWN.

I can't find the watchdog with top or ps

top and ps only display processes. The H2 watchdog is a thread within a java process. To see the thread, use:

jps -l (to get the list of Java processes)
jstack -l <pid> (to get a full thread dump)