[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=14077115#comment-14077115 ] 

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

[~smarlow] [~gbadner]
I can try to disable the L2 cache on this particular flow as you suggested. However we are dealing with a large JEE application. It exposes around 150 services (EJBs) with thousands of operations (public methods). Identifying all the operations that exhibit this "import" pattern is a huge undertaking. We might have operations that do not cause OOM but still require more memory due to this behavior. Out clients might have to use large heap sizes to avoid issues in Production. The fact that, each time a new entity is persisted, the Hibernate session is leaked into the pending-puts cache for 60s seems not normal to me. If we have multiple transactions going on in parallel, each creating a new entity among other things, can lead to a huge number of Hibernate sessions hanging around until they are evicted from pending-puts cache.

So we might have to stick with our workaround which basically removes the leaked pending-puts entry after each entity is persisted by calling PutFromLoadValidator.acquirePutFromLoadLock(). I noticed that the fix attempted tried to avoid the creation of the pending-put entry. But how about trying to remove the entry in case of new entities? This might be a silly suggestion as I don't have the knowledge to really asses if it is feasible. But the workaround that I did seems to be working (see JPAUtil.removePendingPutAfterCreate() in my test app) although it looks like a terrible hack as it uses non public APIs.

> 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: Enhancement
>          Components: JPA / Hibernate
>    Affects Versions: 18.0.1.Final, 19.0.0.Final
>            Reporter: Sorin Potra
>            Assignee: Scott Marlow
>            Priority: Optional
>         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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