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https://issues.apache.org/jira/browse/CASSANDRA-13929?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16361873#comment-16361873
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Jay Zhuang commented on CASSANDRA-13929:
----------------------------------------
I think it's just caching the largest tree ever built
({{[BTree.java:907|https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/utils/btree/BTree.java#L907]}})
and getting bigger and bigger.
Here is an example with a large number of {{IN}} in a CQL, which causes high
heap usage for {{$Stack}} :
{noformat}
session.execute_async("select id from test.users where id in (%s)" %
','.join(map(str, range(100000))))
{noformat}
Here is a dtest to reproduce that:
{{[large_in_test.py|https://github.com/cooldoger/cassandra-dtest/blob/13929/large_in_test.py]}}
{{$Stack}} uses 25% 10M heap: {{10M = 10 (thread) * 100K (element) * 8 (obj
size)}}
!dtest_example_heap.png!
We could increase heap size and then increase thread number, element number
gradually to make {{$Stack}} to 80%+ heap usage. And I'm sure there're other
use cases could build large BTree. Seems the {{$Stack}} is unable to release
until the {{Thread}} is released and we don't that for {{ThreadPoolExecutor}}.
I'd like to propose the following patch which cleans large BTree builder ({{>
1k elements}}) while recycling:
| Branch | uTest |
| [13929-3.11|https://github.com/cooldoger/cassandra/tree/13929-3.11] |
[!https://circleci.com/gh/cooldoger/cassandra/tree/13929-3.11.svg?style=svg!|https://circleci.com/gh/cooldoger/cassandra/tree/13929-3.11]
|
> 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
> 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_heap.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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