[jboss-jira] [JBoss JIRA] (WFLY-13259) Memory leak in Hibernate pending-puts cache when L2 cache is enabled

[Sorin Potra (Jira)]

    [ https://issues.redhat.com/browse/WFLY-13259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14008264#comment-14008264 ] 

Sorin Potra commented on WFLY-13259:
------------------------------------

I modified the web app to call EntityManager.close() in all servlets and the context listener (the only servlet used in the scenario tested is AddChildServlet). This has a beneficial effect on memory usage as the size of the SessionImpl instances has decreased. But the memory leak is still there. I modified the client to execute 3500 transactions before slowing down (initially it was executing 1400 transactions). I kept -Xmx to the default value of 512M. The Child pending-puts cache has a retained heap size of about 180MB after executing 3500 transactions. Please find attached the new web-app and its client (simple-hibernate-war.war.2020-03-25, simple-hibernate-war.zip.2020-03-25, simple-hibernate-war-client.zip.2020-03-25).

The scenario in our production app is a bit different as the entry point is an EJB, not a servlet as in the test app and the production app uses container managed transactions and entity managers. Bur the pending-puts leak is present in both scenarios.

> Memory leak in Hibernate pending-puts cache when L2 cache is enabled
> --------------------------------------------------------------------
>
>                 Key: WFLY-13259
>                 URL: https://issues.redhat.com/browse/WFLY-13259
>             Project: WildFly
>          Issue Type: Bug
>          Components: JPA / Hibernate
>    Affects Versions: 18.0.1.Final, 19.0.0.Final
>            Reporter: Sorin Potra
>            Assignee: Scott Marlow
>            Priority: Critical
>         Attachments: PathToGCRoots_strong_refs.PNG, afterOOM.hprof.zip, beforeOOM.hprof.zip, pending-puts-leak.PNG, simple-hibernate-war-client.zip, simple-hibernate-war-client.zip.2020-03-25, simple-hibernate-war.war, simple-hibernate-war.war.2020-03-25, simple-hibernate-war.zip, simple-hibernate-war.zip.2020-03-25
>
>
> Under certain conditions, described below, WildFly / Hibernate can leak memory into the pending-puts cache eventually causing an OutOfMemoryError. Attached you can find a web application and a standalone client that can be used to reproduce the problem. The web app defines two entities: a Parent and a Child. There is a bidirectional one-to-many relationship between the Parent and the Child. JPA L2 cache is enabled (Infinispan is the cache provider).
> Repeatedly executing a transaction that creates a new Child and adds it to the list of children in the Parent will cause the memory usage to increase steadily until OOM is encountered. If the execution of these transactions is stopped before reaching OOM, the memory will be reclaimed after a few minutes of inactivity.
> Attached you can find the following:
> - simple-hibernate-war.war - the web app that can be deployed in WildFly to reproduce the issue.
> - simple-hibernate-war.zip - the source code for the above web app. The servlet that is invoked by the client to create and persist a new Child is com.microfocus.sa.web.AddChildServlet
> - simple-hibernate-war-client.zip - the standalone client that can be used to invoke the AddChildServlet. After unzipping the archive, the client can be run with the following command from the client folder:
>   
>   java -cp bin com.microfocus.sa.client.AddChildClient
>   
> If you need to run the client multiple times, you have to restart WildFly in between the runs, to start from a fresh state (the web app uses the h2 in memory databasewhich is reset at each restart).
> - pending-puts-leak.PNG - a screeshot from Memory Analyzer showing a leaked SessionImpl instance



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