[PJUG Javamail] What causes "Too many open files" in Tomcat

[Wayne Carstensen]

I don't know if this applies to your problem, but we have had similar 
issues with some libraries not explicitly closing file resources. They 
are expecting that a garbage collection will .close() the file resource 
when the owing object goes out of scope (in your case 
/usr/dict/wordlist.pwd). I can only assume this is because they have the 
.close() sitting in a finalize() method.

In our case, the 'too many files open' occurs when we are opening 
numerous files briefly to calculate the checksums or gather values from 
thousands of files. For the simple cases we forced the garbage collector 
to run with a System.gc(); This is not entirely reliable since there is 
no guarantee that gc will do any work. In a severe case we were forced 
to limit the amount of memory available to the JVM to encourage garbage 
collection early and often so that file handles would be released. 
Needless to say it was a joy to find the right -Xmx value that was low 
enough to encourage enough gc() and large enough to complete the task! 
If I recall, the major offender was the Byte Code Engineering Library 
(BCEL).

If the process is highly repetitious, like a pounding from a test loop 
or simply heavy traffic, this would be an indication that the system has 
been unable to release the file resources timely. The use of 
SurvivorRatio=8 in the recommended JVM parms may be trying to speak to 
this issue since the default is 25.

To debug this, I would look for ways to insert strategic thread sleeps 
and gc() calls to see if the problem is delayed (as in more successful 
iterations) or averted altogether. If either of these approaches work, 
my condolences. It may require the added chore of explicitly setting 
variables to null to encourage more thorough minor garbage collections. 
Since this message is coming from Tomcat activities, your hands are 
definitely tied.

Good luck Rob.

- Wayne


Wayne Carstensen
C-Ware, Inc.

Rob Tanner wrote:
> Hi,
> 
> I’m getting messages like these in the catalina.out log:
> 
>     java.net.SocketException: Too many open files
>     java.io.FileNotFoundException: /usr/dict/wordlist.pwd (Too many open
>     files)
>     java.io.FileNotFoundException:
>     /var/apache/apache-tomcat-5.5.23/webapps/AccountManager/WEB-INF/classes/log4j.properties
>     (Too many open files)
>     java.net.SocketException: Too many open files
> 
> 
> 
> And, of course, I have to stop and restart Tomcat to get it to work 
> again.  This is not a system error; it’s only in Tomcat.  I did some 
> googling and found a suggestion with regard to Java arguments when 
> Tomcat starts up.  
> 
> These are the options I’m starting Tomcat with: '-XX:NewSize=128m 
> -XX:MaxNewSize=128m -XX:SurvivorRatio=8 -Xms256m -Xmx512m'
> 
> I’ve also gone through the most active apps and made sure that I was not 
> leaving any database or LDAP connections open.
> 
> Any ideas?
> 
> Thanks,
> Rob
> 
> 
> 
> *Rob Tanner
> *JAVA Developer
> Linfield College, McMinnville Oregon