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https://issues.apache.org/jira/browse/HBASE-15991?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15326918#comment-15326918
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Eshcar Hillel commented on HBASE-15991:
---------------------------------------
Some comments:
1. The exception is due to StealJobQueue extending PriorityBlockingQueue which
throws the exception when it cannot determine the position of the item in the
queue. I agree there is no need in a priority queue for the in-memory flush, at
least for now. If it is required in the future the attribute for comparison
will become obvious as well.
2. We should consider the pros/cons of LinkedBlockingQueue vs other queue such
as ConcurrentLinkedQueue.
see in
http://stackoverflow.com/questions/1301691/java-queue-implementations-which-one
"The most important difference between LinkedBlockingQueue and
ConcurrentLinkedQueue is that if you request an element from a
LinkedBlockingQueue and the queue is empty, your thread will wait until there
is something there. A ConcurrentLinkedQueue will return right away with the
behavior of an empty queue."
on the other hand in ConcurrentLinkedQueue
"Beware that, unlike in most collections, the size method is NOT a
constant-time operation. Because of the asynchronous nature of these queues,
determining the current number of elements requires a traversal of the
elements."
So we need to consider what is more important having a size method with
constant time, or making sure retrieving an element never blocks.
> CompactingMemstore#InMemoryFlushRunnable should implement
> Comparable/Comparator
> -------------------------------------------------------------------------------
>
> Key: HBASE-15991
> URL: https://issues.apache.org/jira/browse/HBASE-15991
> Project: HBase
> Issue Type: Sub-task
> Affects Versions: 2.0.0
> Reporter: ramkrishna.s.vasudevan
> Assignee: ramkrishna.s.vasudevan
> Priority: Critical
> Fix For: 2.0.0
>
> Attachments: HBASE-15991.patch, HBASE-15991_test.patch
>
>
> Configuring CompactingMemstore for a table fails due to the following error
> {code}
> 2016-06-08 23:27:03,761 ERROR [B.defaultRpcServer.handler...
> 2016-06-08 23:27:03,761 ERROR
> [B.defaultRpcServer.handler=38,queue=8,port=16041] ipc.RpcServer: Unexpected
> throwable object
> java.lang.ClassCastException:
> org.apache.hadoop.hbase.regionserver.CompactingMemStore$InMemoryFlushRunnable
> cannot be cast to java.lang.Comparable
> at
> java.util.concurrent.PriorityBlockingQueue.siftUpComparable(PriorityBlockingQueue.java:357)
> at
> java.util.concurrent.PriorityBlockingQueue.offer(PriorityBlockingQueue.java:489)
> at
> org.apache.hadoop.hbase.util.StealJobQueue$1.offer(StealJobQueue.java:56)
> at
> java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1361)
> at
> org.apache.hadoop.hbase.regionserver.CompactingMemStore.checkActiveSize(CompactingMemStore.java:258)
> at
> org.apache.hadoop.hbase.regionserver.AbstractMemStore.internalAdd(AbstractMemStore.java:403)
> at
> org.apache.hadoop.hbase.regionserver.AbstractMemStore.add(AbstractMemStore.java:113)
> at org.apache.hadoop.hbase.regionserver.HStore.add(HStore.java:630)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.applyToMemstore(HRegion.java:3769)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.applyFamilyMapToMemstore(HRegion.java:3740)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.doMiniBatchMutate(HRegion.java:3222)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.batchMutate(HRegion.java:2954)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.batchMutate(HRegion.java:2896)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.doBatchOp(RSRpcServices.java:868)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.doNonAtomicRegionMutation(RSRpcServices.java:830)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.multi(RSRpcServices.java:2307)
> at
> org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:34826)
>
> {code}
> It is a straight forward fix. But If we implement the Comparable the
> compareTo() should be based on what attribute? Should be based on the time?
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