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https://issues.apache.org/jira/browse/CASSANDRA-13929?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16363884#comment-16363884
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Thomas Steinmaurer edited comment on CASSANDRA-13929 at 2/14/18 12:51 PM:
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[~norman], a concrete example for a *single* Recycler$Stack instance from our 
loadtest.
!memleak_heapdump_recyclerstack.png|width=300!

Looks like we have a lot of largish 32K object arrays, which seem to be empty 
as shallow heap = retained heap for this object arrays. So, a quick look on the 
patch of [~jay.zhuang], this might help. [~jjirsa], will re-patch a single node 
and report back after a considerable uptime.


was (Author: tsteinmaurer):
[~norman], a concrete example for a single Recycler$Stack instance:
!memleak_heapdump_recyclerstack.png|width=300!

Looks like we have a lot of largish 32K object arrays, which seem to be empty 
as shallow heap = retained heap for this object arrays. So, a quick look on the 
patch of [~jay.zhuang], this might help. [~jjirsa], will re-patch a single node 
and report back after a considerable uptime.

> BTree$Builder / io.netty.util.Recycler$Stack leaking memory
> -----------------------------------------------------------
>
>                 Key: CASSANDRA-13929
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13929
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Thomas Steinmaurer
>            Assignee: Jay Zhuang
>            Priority: Major
>             Fix For: 3.11.x
>
>         Attachments: cassandra_3.11.0_min_memory_utilization.jpg, 
> cassandra_3.11.1_NORECYCLE_memory_utilization.jpg, 
> cassandra_3.11.1_mat_dominator_classes.png, 
> cassandra_3.11.1_mat_dominator_classes_FIXED.png, 
> cassandra_3.11.1_snapshot_heaputilization.png, 
> cassandra_3.11.1_vs_3.11.2recyclernullingpatch.png, 
> dtest_example_80_request.png, dtest_example_80_request_fix.png, 
> dtest_example_heap.png, memleak_heapdump_recyclerstack.png
>
>
> Different to CASSANDRA-13754, there seems to be another memory leak in 
> 3.11.0+ in BTree$Builder / io.netty.util.Recycler$Stack.
> * heap utilization increase after upgrading to 3.11.0 => 
> cassandra_3.11.0_min_memory_utilization.jpg
> * No difference after upgrading to 3.11.1 (snapshot build) => 
> cassandra_3.11.1_snapshot_heaputilization.png; thus most likely after fixing 
> CASSANDRA-13754, more visible now
> * MAT shows io.netty.util.Recycler$Stack as top contributing class => 
> cassandra_3.11.1_mat_dominator_classes.png
> * With -Xmx8G (CMS) and our load pattern, we have to do a rolling restart 
> after ~ 72 hours
> Verified the following fix, namely explicitly unreferencing the 
> _recycleHandle_ member (making it non-final). In 
> _org.apache.cassandra.utils.btree.BTree.Builder.recycle()_
> {code}
>         public void recycle()
>         {
>             if (recycleHandle != null)
>             {
>                 this.cleanup();
>                 builderRecycler.recycle(this, recycleHandle);
>                 recycleHandle = null; // ADDED
>             }
>         }
> {code}
> Patched a single node in our loadtest cluster with this change and after ~ 10 
> hours uptime, no sign of the previously offending class in MAT anymore => 
> cassandra_3.11.1_mat_dominator_classes_FIXED.png
> Can' say if this has any other side effects etc., but I doubt.



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