|Summary:||Reloading context orphans currently open jndi datasource connections|
|Product:||Tomcat 4||Reporter:||Wayne Schroeder <raz>|
|Component:||Unknown||Assignee:||Tomcat Developers Mailing List <dev>|
Description Wayne Schroeder 2003-11-27 21:15:10 UTC
I fiddled around with this a while and have determined to the best of my ability that this is a real bug. I have a jndi datasource connected to a postgresql server. I have two jndi resources (a reader and writer) so that later I can implement a system with replication etc and deal with writes and reads to different connections. To summarize, after using the system, there are two connections to postgres that get reused -- one reader and writer. Under load, this number increases and will slowly go back down. I usually end up with two idle connections (one reader and one writer) left under no load. If you reload the context where the datasource is at (it's a context specific datasource), the number of connections will jump by two when used. Each reload produces 2 more connections min until I restart the server. It appears that after a reload, the 'persisted connections' get abandoned / orphaned. Eventually, I hit my max connections and cannot aquire any more and the system fails. I have tried the abandond collection parameters and have added debug logging to my code to ensure that I am indeed calling close on the connections I checkout, even on exceptions and error cases. Under normal useage without reloads, no connection leakage happens. This is on a solaris 8 machine with the 4.1.27-hotfix-22096.tar.gz applied. Let me know if more information is required. I have this in a development environment and can let somone attach in jdb and hammer on the thing since it's not a production system -- if that will help in getting a repro. Wayne
Comment 1 Glenn Nielsen 2003-12-06 16:38:26 UTC
I have verified your bug report. If this is happening with a JNDI Named DataSource it might also be happening with other JNDI resources created. And be a source of a memory leak. Great bug report. I don't have a solution yet, but will be researching this. Thanks Wayne
Comment 2 Remy Maucherat 2003-12-06 16:47:57 UTC
I think the only clean way to "fix" this is to define the data source as global, and use links. There's no API in JNDI for releasing resources, so ... (and I don't want to introduce any proprietary APIs either). Maybe waiting for GC would be the solution, and maybe there's a memory leak associated with the JNDI context.
Comment 3 Glenn Nielsen 2003-12-07 17:34:01 UTC
Yes, it may be that when the JNDI resource is defined within a Context and the context is reloaded or stopped, the previous JNDI objects may still consume their resources including db connections until they are GC'd. At a minimum we need to verify whether the already existing resources become eligible for GC after a reload/stop of a Context and there is no memory/resource leak. Even if there is no memory leak and the previous JNDI DataSource becomes eligible for GC it might be nice to explicitly close the db connections. If the DBCP DataSource is being used a possible solution to free up resources would be a Context LifeCycle Listener that does a close on the DBCP DataSource during a Context reload/stop.
Comment 4 Mark Thomas 2005-06-08 01:20:26 UTC
I have confirmed that with the latest code for 4.1.x that the orphaned connections are eligible for garbage collection. It is possible, but I have not confirmed it, that as a result of bug 20758 these connections were not eligible for gc in 4.1.30 and earlier but this is only speculation on my part. I agree with Glenn that it is possible that some explicit clean-up could be performed using a Context LifeCycle Listener but this is a 'nice to have'. Therefore, since there is no memory leak here, I am changing this issue to an enhancement.
Comment 5 Rafael Leite 2007-04-11 07:57:55 UTC
Hey Mark! I respectfully disagree with you about this being a enhancement. If the datasources are left to be garbage collected, their connections with the database remain opened (as i just experienced on Tomcat 5.0.28). Since most database installations rely on a maximum number of connections, the new datasource resulting of the context's reload might not be able to connect to the database, right? If these affirmations are right, IMHO this issue is a bug. What do you think? Thank you for your time! :)
Comment 6 Cyril Bonté 2011-02-05 16:32:22 UTC
Hi, I wanted to open a bug report but finally found this old one. (In reply to comment #4) > I agree with Glenn that it is possible that some explicit clean-up could be > performed using a Context LifeCycle Listener but this is a 'nice to have'. > Therefore, since there is no memory leak here, I am changing this issue to an > enhancement. I don't totally agree because some pool configurations can cause a memory leak (due to a thread leak). For example, when DBCP is configured with timeBetweenEvictionRunsMillis > 0, the thread won't stop at reload. After several reloads, PermGen becomes full. This is still true with Tomcat 7.
Comment 7 Mark Thomas 2011-03-08 17:20:28 UTC
A LifecycleListener isn't necessarily the best place for this and it would require explicit configuration. I have added some clean-up for DataSource resources when naming resources are stopped but this is far from a generic solution for all resources (and neither is it meant to be). As Remy points out what is needed is a standard interface for releasing JNDI resources. DataSources are sufficiently widely used and the issues sufficiently problematic that I think it makes sense to address them. The clean-up has been added to Tomcat 7 and will be included in 7.0.11 onwards. Regarding the thread leak with Commons DBCP, that is a Commons DBCP bug although one that might be hard to fix.