Tom van der Woerdt created CASSANDRA-13810:
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Summary: Overload because of hint pressure + MVs
Key: CASSANDRA-13810
URL: https://issues.apache.org/jira/browse/CASSANDRA-13810
Project: Cassandra
Issue Type: Bug
Reporter: Tom van der Woerdt
Cluster setup: 3 DCs, 20 Cassandra nodes each, all 3.0.14, with approx. 200GB
data per machine. Many tables have MVs associated.
During some maintenance we did a rolling restart of all nodes in the cluster.
This caused a buildup of hints/batches, as expected. Most nodes came back just
fine, except for two nodes.
These two nodes came back with a loadavg of >100, and 'nodetool tpstats' showed
a million (not exaggerating) MutationStage tasks per second(!). It was clear
that these were mostly (all?) mutations coming from hints, as indicated by
thousands of log entries per second in debug.log :
{noformat}
DEBUG [SharedPool-Worker-107] 2017-08-27 13:16:51,098 HintVerbHandler.java:95 -
Failed to apply hint
java.util.concurrent.CompletionException:
org.apache.cassandra.exceptions.WriteTimeoutException: Operation timed out -
received only 0 responses.
at
java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:292)
~[na:1.8.0_144]
at
java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:308)
~[na:1.8.0_144]
at
java.util.concurrent.CompletableFuture.uniAccept(CompletableFuture.java:647)
~[na:1.8.0_144]
at
java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:632)
~[na:1.8.0_144]
at
java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:474)
~[na:1.8.0_144]
at
java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:1977)
~[na:1.8.0_144]
at org.apache.cassandra.db.Keyspace.applyInternal(Keyspace.java:481)
~[apache-cassandra-3.0.14.jar:3.0.14]
at
org.apache.cassandra.db.Keyspace.lambda$applyInternal$0(Keyspace.java:495)
~[apache-cassandra-3.0.14.jar:3.0.14]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
~[na:1.8.0_144]
at
org.apache.cassandra.concurrent.AbstractLocalAwareExecutorService$FutureTask.run(AbstractLocalAwareExecutorService.java:164)
~[apache-cassandra-3.0.14.jar:3.0.14]
at org.apache.cassandra.concurrent.SEPWorker.run(SEPWorker.java:105)
~[apache-cassandra-3.0.14.jar:3.0.14]
at java.lang.Thread.run(Thread.java:748) ~[na:1.8.0_144]
Caused by: org.apache.cassandra.exceptions.WriteTimeoutException: Operation
timed out - received only 0 responses.
... 6 common frames omitted
{noformat}
After reading the relevant code, it seems that a hint is considered droppable,
and in the mutation path when the table contains a MV and the lock fails to
acquire and the mutation is droppable, it throws a WTE without waiting until
the timeout expires. This explains why Cassandra is able to process a million
mutations per second without actually considering them 'dropped' in the
'nodetool tpstats' output.
I managed to recover the two nodes by stopping handoffs on all nodes in the
cluster and reenabling them one at a time. It's likely that the hint/batchlog
settings were sub-optimal on this cluster, but I think that the retry
behavior(?) of hints should be improved as it's hard to express hint throughput
in kb/s when the mutations can involve MVs.
More data available upon request -- I'm not sure which bits are relevant and
which aren't.
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