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https://issues.apache.org/jira/browse/HBASE-18158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16036309#comment-16036309
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Ted Yu commented on HBASE-18158:
--------------------------------
Nice finding.
MyCompactingMemStoreWithCustomeCompactor ->
MyCompactingMemStoreWithCustomCompactor
> Two running in-memory compaction threads may lose data
> ------------------------------------------------------
>
> Key: HBASE-18158
> URL: https://issues.apache.org/jira/browse/HBASE-18158
> Project: HBase
> Issue Type: Bug
> Affects Versions: 2.0.0
> Reporter: Chia-Ping Tsai
> Assignee: Chia-Ping Tsai
> Fix For: 2.0.0
>
> Attachments: HBASE-18158.v0.patch
>
>
> {code:title=CompactingMemStore.java|borderStyle=solid}
> private void stopCompaction() {
> if (inMemoryFlushInProgress.get()) {
> compactor.stop();
> inMemoryFlushInProgress.set(false);
> }
> }
> {code}
> The stopCompaction() set inMemoryFlushInProgress to false so there may be two
> in-memory compaction threads which execute simultaneously. If there are two
> running InMemoryFlushRunnable, the later InMemoryFlushRunnable may change the
> versionedList.
> {code:title=MemStoreCompactor.java|borderStyle=solid}
> public boolean start() throws IOException {
> if (!compactingMemStore.hasImmutableSegments()) { // no compaction on
> empty pipeline
> return false;
> }
> // get a snapshot of the list of the segments from the pipeline,
> // this local copy of the list is marked with specific version
> versionedList = compactingMemStore.getImmutableSegments();
> {code}
> And the first InMemoryFlushRunnable will use the chagned versionedList to
> remove the corresponding segments.
> {code:title=MemStoreCompactor#doCompaction|borderStyle=solid}
> if (!isInterrupted.get()) {
> if (resultSwapped = compactingMemStore.swapCompactedSegments(
> versionedList, result, (action==Action.MERGE))) {
> // update the wal so it can be truncated and not get too long
> compactingMemStore.updateLowestUnflushedSequenceIdInWAL(true); //
> only if greater
> }
> }
> {code}
> In conclusion, first InMemoryFlushRunnable will remove the worng segment. And
> the later InMemoryFlushRunnable will introduce NPE because first
> InMemoryFlushRunnable set versionedList to null after compaction.
> {code}
> Exception in thread
> "RpcServer.default.FPBQ.Fifo.handler=3,queue=0,port=45712-inmemoryCompactions-1496563908038"
> java.lang.NullPointerException
> at
> org.apache.hadoop.hbase.regionserver.CompactionPipeline.swap(CompactionPipeline.java:119)
> at
> org.apache.hadoop.hbase.regionserver.CompactingMemStore.swapCompactedSegments(CompactingMemStore.java:283)
> at
> org.apache.hadoop.hbase.regionserver.MemStoreCompactor.doCompaction(MemStoreCompactor.java:212)
> at
> org.apache.hadoop.hbase.regionserver.MemStoreCompactor.start(MemStoreCompactor.java:122)
> at
> org.apache.hadoop.hbase.regionserver.CompactingMemStore.flushInMemory(CompactingMemStore.java:388)
> at
> org.apache.hadoop.hbase.regionserver.CompactingMemStore$InMemoryFlushRunnable.run(CompactingMemStore.java:500)
> at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> {code}
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