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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17379) Lack of synchronization in CompactionPipeline#getScanners()
Date Wed, 28 Dec 2016 17:44:58 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17379?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15783353#comment-15783353
] 

stack commented on HBASE-17379:
-------------------------------

bq. stack I agree we should minimize synchronization. But we do need some synchronization
to avoid ConcurrentModificationException in such cases.

We have worked with this pattern elsewhere [~eshcar]. Lets be careful adding in new locking.
Crossing the synchronization may be fast when uncontended but when many threads,  it requires
coordination which throttles throughput.

In other places we've done copy-on-write or we've done explicit versioned views (changes in
pipeline happen orders of magnitude less often than gets... we should make use of this fact).
I can try dig up a soln. that would work here if needed if it'd help.

Meantime, let us revert the aggravating patch, HBASE-17081 so you can have the weekend free.

> Lack of synchronization in CompactionPipeline#getScanners()
> -----------------------------------------------------------
>
>                 Key: HBASE-17379
>                 URL: https://issues.apache.org/jira/browse/HBASE-17379
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 2.0.0
>            Reporter: Ted Yu
>            Assignee: Ted Yu
>         Attachments: 17379.v1.txt, 17379.v2.txt, 17379.v3.txt, 17379.v4.txt, 17379.v5.txt
>
>
> From https://builds.apache.org/job/PreCommit-HBASE-Build/5053/testReport/org.apache.hadoop.hbase.regionserver/TestHRegionWithInMemoryFlush/testWritesWhileGetting/
:
> {code}
> java.io.IOException: java.util.ConcurrentModificationException
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.handleException(HRegion.java:5886)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.initializeScanners(HRegion.java:5856)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.<init>(HRegion.java:5819)
> 	at org.apache.hadoop.hbase.regionserver.HRegion.instantiateRegionScanner(HRegion.java:2786)
> 	at org.apache.hadoop.hbase.regionserver.HRegion.getScanner(HRegion.java:2766)
> 	at org.apache.hadoop.hbase.regionserver.HRegion.get(HRegion.java:7036)
> 	at org.apache.hadoop.hbase.regionserver.HRegion.get(HRegion.java:7015)
> 	at org.apache.hadoop.hbase.regionserver.HRegion.get(HRegion.java:6994)
> 	at org.apache.hadoop.hbase.regionserver.TestHRegion.testWritesWhileGetting(TestHRegion.java:4141)
> 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
> 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> 	at java.lang.reflect.Method.invoke(Method.java:498)
> 	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
> 	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
> 	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
> 	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
> 	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
> 	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
> 	at org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:55)
> 	at org.junit.rules.RunRules.evaluate(RunRules.java:20)
> 	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
> 	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
> 	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
> 	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
> 	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
> 	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
> 	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
> 	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
> 	at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:298)
> 	at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:292)
> 	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
> 	at java.lang.Thread.run(Thread.java:745)
> Caused by: java.util.ConcurrentModificationException: null
> 	at java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:966)
> 	at java.util.LinkedList$ListItr.next(LinkedList.java:888)
> 	at org.apache.hadoop.hbase.regionserver.CompactionPipeline.getScanners(CompactionPipeline.java:220)
> 	at org.apache.hadoop.hbase.regionserver.CompactingMemStore.getScanners(CompactingMemStore.java:298)
> 	at org.apache.hadoop.hbase.regionserver.HStore.getScanners(HStore.java:1154)
> 	at org.apache.hadoop.hbase.regionserver.Store.getScanners(Store.java:97)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.getScannersNoCompaction(StoreScanner.java:353)
> 	at org.apache.hadoop.hbase.regionserver.StoreScanner.<init>(StoreScanner.java:210)
> 	at org.apache.hadoop.hbase.regionserver.HStore.createScanner(HStore.java:1892)
> 	at org.apache.hadoop.hbase.regionserver.HStore.getScanner(HStore.java:1880)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.initializeScanners(HRegion.java:5842)
> 	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.<init>(HRegion.java:5819)
> 	at org.apache.hadoop.hbase.regionserver.HRegion.instantiateRegionScanner(HRegion.java:2786)
> 	at org.apache.hadoop.hbase.regionserver.HRegion.getScanner(HRegion.java:2766)
> 	at org.apache.hadoop.hbase.regionserver.HRegion.get(HRegion.java:7036)
> {code}
> The cause is in CompactionPipeline#getScanners() where there is no synchronization around
iterating pipeline.
> The code causing ConcurrentModificationException:
> {code}
>     for (Segment segment : this.pipeline) {
> {code}
> was introduced by HBASE-17081



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