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https://issues.apache.org/jira/browse/CASSANDRA-13929?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16504704#comment-16504704
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Jason Brown commented on CASSANDRA-13929:
-----------------------------------------
On the whole, this looks pretty good. I'm running tests locally now, and will
run in circleci shortly.
[~jay.zhuang] There's one thing I'm wondering: in {{#reuse{}}}, we do not
explicitly null out the {{values}} array, like we used to do in {{#cleanup()}}:
{code}
Arrays.fill(values, null);
{code}
While every access of {{values}} seems safe, and uses the {{count}} to ensure
proper sizing of any built {{Object[]}}, I'd like to be over-cautious and null
out the array to prevent the possibility of data leak wherein a reuse of
Builder erroneously gets extra data from the last use. This error doesn't seem
like it's possible in the current code, but I'd like to future-proof this - I'd
be a complete nightmare to debug.
wdyt?
> 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: 3.11.3
>
> 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,
> cassandra_heapcpu_memleak_patching_test_30d.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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