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https://issues.apache.org/jira/browse/CASSANDRA-7743?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14096631#comment-14096631
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Benedict commented on CASSANDRA-7743:
-------------------------------------
I haven't got to that stage yet, I'm just analysing the code right now. It's
why I asked for your input, was hoping you could disabuse me if I'm completely
wrong. I don't 100% understand the control flow, as it doesn't make much sense
(to me) to be adding it to a different cache. However if you look in
PooledByteBuf.deallocate(), it calls PoolArena.free() to release the memory,
which in turn calls parent.threadCache.get().add() to cache its memory;
obviously the threadCache.get() is grabbing the threadlocal cache for the
thread releasing, not the source PoolThreadCache.
Also worth noting I'm not convinced that, even if I'm correct, this fully
explains the behaviour. We should only release on a different thread if an
exception occurs during processing anyway, so I'm still digging for a more
satisfactory full explanation of the behaviour.
> Possible C* OOM issue during long running test
> ----------------------------------------------
>
> Key: CASSANDRA-7743
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7743
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Environment: Google Compute Engine, n1-standard-1
> Reporter: Pierre Laporte
> Assignee: Benedict
> Fix For: 2.1.0
>
>
> During a long running test, we ended up with a lot of
> "java.lang.OutOfMemoryError: Direct buffer memory" errors on the Cassandra
> instances.
> Here is an example of stacktrace from system.log :
> {code}
> ERROR [SharedPool-Worker-1] 2014-08-11 11:09:34,610 ErrorMessage.java:218 -
> Unexpected exception during request
> java.lang.OutOfMemoryError: Direct buffer memory
> at java.nio.Bits.reserveMemory(Bits.java:658) ~[na:1.7.0_25]
> at java.nio.DirectByteBuffer.<init>(DirectByteBuffer.java:123)
> ~[na:1.7.0_25]
> at java.nio.ByteBuffer.allocateDirect(ByteBuffer.java:306)
> ~[na:1.7.0_25]
> at io.netty.buffer.PoolArena$DirectArena.newChunk(PoolArena.java:434)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at io.netty.buffer.PoolArena.allocateNormal(PoolArena.java:179)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at io.netty.buffer.PoolArena.allocate(PoolArena.java:168)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at io.netty.buffer.PoolArena.allocate(PoolArena.java:98)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at
> io.netty.buffer.PooledByteBufAllocator.newDirectBuffer(PooledByteBufAllocator.java:251)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at
> io.netty.buffer.AbstractByteBufAllocator.directBuffer(AbstractByteBufAllocator.java:155)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at
> io.netty.buffer.AbstractByteBufAllocator.directBuffer(AbstractByteBufAllocator.java:146)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at
> io.netty.buffer.AbstractByteBufAllocator.ioBuffer(AbstractByteBufAllocator.java:107)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at
> io.netty.channel.AdaptiveRecvByteBufAllocator$HandleImpl.allocate(AdaptiveRecvByteBufAllocator.java:104)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at
> io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:112)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at
> io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:507)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at
> io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:464)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at
> io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:378)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:350)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at
> io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116)
> ~[netty-all-4.0.20.Final.jar:4.0.20.Final]
> at java.lang.Thread.run(Thread.java:724) ~[na:1.7.0_25]
> {code}
> The test consisted of a 3-nodes cluster of n1-standard-1 GCE instances (1
> vCPU, 3.75 GB RAM) running cassandra-2.1.0-rc5, and a n1-standard-2 instance
> running the test.
> After ~2.5 days, several requests start to fail and we see the previous
> stacktraces in the system.log file.
> The output from linux ‘free’ and ‘meminfo’ suggest that there is still memory
> available.
> {code}
> $ free -m
> total used free shared buffers cached
> Mem: 3702 3532 169 0 161 854
> -/+ buffers/cache: 2516 1185
> Swap: 0 0 0
> $ head -n 4 /proc/meminfo
> MemTotal: 3791292 kB
> MemFree: 173568 kB
> Buffers: 165608 kB
> Cached: 874752 kB
> {code}
> These errors do not affect all the queries we run. The cluster is still
> responsive but is unable to display tracing information using cqlsh :
> {code}
> $ ./bin/nodetool --host 10.240.137.253 status duration_test
> Datacenter: DC1
> ===============
> Status=Up/Down
> |/ State=Normal/Leaving/Joining/Moving
> -- Address Load Tokens Owns (effective) Host ID
> Rack
> UN 10.240.98.27 925.17 KB 256 100.0%
> 41314169-eff5-465f-85ea-d501fd8f9c5e RAC1
> UN 10.240.137.253 1.1 MB 256 100.0%
> c706f5f9-c5f3-4d5e-95e9-a8903823827e RAC1
> UN 10.240.72.183 896.57 KB 256 100.0%
> 15735c4d-98d4-4ea4-a305-7ab2d92f65fc RAC1
> $ echo 'tracing on; select count(*) from duration_test.ints;' | ./bin/cqlsh
> 10.240.137.253
> Now tracing requests.
> count
> -------
> 9486
> (1 rows)
> Statement trace did not complete within 10 seconds
> {code}
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