# Cluster not processing write cypher

**URL:** <https://community.neo4j.com/t/cluster-not-processing-write-cypher/13694>\
**Category:** Cluster\
**Tags:** performance, cluster\
**Created:** [January 16, 2020, 12:33pm UTC](https://community.neo4j.com/t/cluster-not-processing-write-cypher/13694 "2020-01-16T12:33:21Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![mdfrenchman](https://sea1.discourse-cdn.com/flex021/user_avatar/community.neo4j.com/mdfrenchman/32/6094_2.png) [@mdfrenchman](https://community.neo4j.com/u/mdfrenchman)\
**Post date:** [January 16, 2020, 12:33pm UTC](https://community.neo4j.com/t/cluster-not-processing-write-cypher/13694/1 "2020-01-16T12:33:22Z")

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We have a cluster of 3 servers (normal config, leader is read/write, 2 followers are read).

We're having an issue of WRITE queries not completing, they're eventually returning an OOM exception.

The cypher (with labels and props obsfucated):

```auto
UNWIND ["01", "02", "03", "04", "05", "06", "07", "08", "09"] as pnum
MATCH (:Thing {thingUniqueNumber:pnum})-[r:REL_TO_DELETE]->()
RETURN pnum, r

```

returns in 13ms with 27 results.

Replacing the RETURN with `DELETE r` carries on for hours till a log message is reported with oom (I'll update with the actual message if I can).

Possibly related, one of our followers wasn't picking up the heartbeat and getting replicated transactions from the leader after being restarted earlier in the week. The cluster\_state folder was cleared as the recommended solution for that.

Thanks for any help!

-Mike French

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<div class="post-metadata">

**Author:** ![mdfrenchman](https://sea1.discourse-cdn.com/flex021/user_avatar/community.neo4j.com/mdfrenchman/32/6094_2.png) [@mdfrenchman](https://community.neo4j.com/u/mdfrenchman)\
**Post date:** [January 16, 2020, 3:27pm UTC](https://community.neo4j.com/t/cluster-not-processing-write-cypher/13694/2 "2020-01-16T15:27:59Z")

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A reboot of the cluster has resolved the issue. Further investigation returned this:  
ERROR LEAK: ByteBuf.release() was not called before it's garbage-collected. See [Netty.docs: Reference counted objects](http://netty.io/wiki/reference-counted-objects.html) for more information.

What MAY have caused that....  
There were 2 sessions, one adding labels and one removing a different label from the same subset of nodes. That may have caused lock contention.

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**Author:** ![jeremie](https://sea1.discourse-cdn.com/flex021/user_avatar/community.neo4j.com/jeremie/32/3763_2.png) [@jeremie](https://community.neo4j.com/u/jeremie)\
**Post date:** [January 16, 2020, 5:32pm UTC](https://community.neo4j.com/t/cluster-not-processing-write-cypher/13694/3 "2020-01-16T17:32:51Z")

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Hello Mike,

Which version are you using.  
Are you able to reproduce it?

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<div class="post-metadata">

**Author:** ![mdfrenchman](https://sea1.discourse-cdn.com/flex021/user_avatar/community.neo4j.com/mdfrenchman/32/6094_2.png) [@mdfrenchman](https://community.neo4j.com/u/mdfrenchman)\
**Post date:** [January 16, 2020, 6:14pm UTC](https://community.neo4j.com/t/cluster-not-processing-write-cypher/13694/4 "2020-01-16T18:14:57Z")

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enterprise version 3.5.5 and we haven't been able to reproduce it yet.

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<div class="post-metadata">

**Author:** ![jeremie](https://sea1.discourse-cdn.com/flex021/user_avatar/community.neo4j.com/jeremie/32/3763_2.png) [@jeremie](https://community.neo4j.com/u/jeremie)\
**Post date:** [January 19, 2020, 6:10am UTC](https://community.neo4j.com/t/cluster-not-processing-write-cypher/13694/5 "2020-01-19T06:10:30Z")

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1. Can you try to update to the latest maintenance release available?

2. Did you notice some GC pause on any node of the cluster ?  
you should have messages like this in in debug.log `Detected VM stop-the-world`  
as mentionned in [Fatal error occurred when handling a client connection causes crash](https://community.neo4j.com/t/fatal-error-occurred-when-handling-a-client-connection-causes-crash/9005)  
or  
in neo4j.log : java.lang.OutOfMemoryError: Java heap space