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Posted to issues@hbase.apache.org by "Hudson (Jira)" <ji...@apache.org> on 2021/11/02 02:35:00 UTC
[jira] [Commented] (HBASE-26384) Segment already flushed to hfile
may still be remained in CompactingMemStore
[ https://issues.apache.org/jira/browse/HBASE-26384?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17437107#comment-17437107 ]
Hudson commented on HBASE-26384:
--------------------------------
Results for branch branch-2.4
[build #228 on builds.a.o|https://ci-hadoop.apache.org/job/HBase/job/HBase%20Nightly/job/branch-2.4/228/]: (x) *{color:red}-1 overall{color}*
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details (if available):
(/) {color:green}+1 general checks{color}
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(x) {color:red}-1 jdk8 hadoop2 checks{color}
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(/) {color:green}+1 jdk8 hadoop3 checks{color}
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(/) {color:green}+1 source release artifact{color}
-- See build output for details.
(/) {color:green}+1 client integration test{color}
> Segment already flushed to hfile may still be remained in CompactingMemStore
> -----------------------------------------------------------------------------
>
> Key: HBASE-26384
> URL: https://issues.apache.org/jira/browse/HBASE-26384
> Project: HBase
> Issue Type: Bug
> Components: in-memory-compaction
> Affects Versions: 3.0.0-alpha-1, 2.4.8
> Reporter: chenglei
> Assignee: chenglei
> Priority: Major
> Labels: branch-2
> Fix For: 2.5.0, 3.0.0-alpha-2, 2.4.9
>
>
> When {{CompactingMemStore}} prepares flushing, {{CompactingMemStore.snapshot}} invokes following {{CompactingMemStore.pushPipelineToSnapshot}} method to get {{Snapshot}}, following line 570 and line 575 uses {{CompactionPipeline#version}} to track whether the Segments in {{CompactionPipeline#pipeline}} has changed since it gets {{VersionedSegmentsList}} in line 570 before emptying {{CompactionPipeline#pipeline}} in line 575.
> {code:java}
> 565 private void pushPipelineToSnapshot() {
> 566 int iterationsCnt = 0;
> 567 boolean done = false;
> 568 while (!done) {
> 569 iterationsCnt++;
> 570 VersionedSegmentsList segments = pipeline.getVersionedList();
> 571 pushToSnapshot(segments.getStoreSegments());
> 572 // swap can return false in case the pipeline was updated by ongoing compaction
> 573 // and the version increase, the chance of it happenning is very low
> 574 // In Swap: don't close segments (they are in snapshot now) and don't update the region size
> 575 done = pipeline.swap(segments, null, false, false);
> .......
> }
> {code}
> However, when {{CompactingMemStore#inMemoryCompaction}} executes {{CompactionPipeline#flattenOneSegment}}, it does not change {{CompactionPipeline#version}} , if there is an {{in memeory compaction}} which executes {{CompactingMemStore#flattenOneSegment}} between above line 570 and line 575, the {{CompactionPipeline#version}} not change, but the {{Segment}} in {{CompactionPipeline}} has changed. Because {{CompactionPipeline#version}} not change, {{pipeline.swap}} in above line 575 could think it is safe to invoke following {{CompactionPipeline#swapSuffix}} method to remove {{Segment}} in {{CompactionPipeline}} , but the {{Segment}} in {{CompactionPipeline}} has changed because of {{CompactingMemStore#flattenOneSegment}} , so the {{Segment}} not removed in following line 295 and still remaining in {{CompactionPipeline}}.
> {code:java}
> 293 private void swapSuffix(List<? extends Segment> suffix, ImmutableSegment segment,
> 294 boolean closeSegmentsInSuffix) {
> 295 pipeline.removeAll(suffix);
> 296 if(segment != null) pipeline.addLast(segment);
> ....
> {code}
> However {{CompactingMemStore.snapshot}} think it is successful and continues to flush the {{Segment}} got by {{CompactingMemStore.snapshot}} as normal, but the {{Segment}} with the same cells still be left in {{CompactingMemStore}}. Leaving {{Segment}} which already flushed in {{MemStore}} is dangerous: if a Major Compaction before the left {{Segment}} flushing, there may be data erroneous.
> My Fix in the PR is as following:
> # Increasing the {{CompactionPipeline#version}} in {{CompactingMemStore#flattenOneSegment}} .
> Branch-2 has this problem but master not， because the branch-2 patch for HBASE-18375 omitting this.
> # For {{CompactionPipeline#swapSuffix}} , explicitly checking that the {{Segment}} in {{suffix}} input parameter is same as the {{Segment}} in {{pipeline}} one by one from
> the last element to the first element of {{suffix}} ， I think explicitly throwing Exception is better than hiding error and causing subtle problem.
> I made separate PRs for master and branch-2 so the code for master and brach-2 could consistent and master could also has UTs for this problem.
> [PR#3777|https://github.com/apache/hbase/pull/3777] is for master and [PR#3779|https://github.com/apache/hbase/pull/3779] is for branch-2.The difference between them is patch for brach-2 including following code in {{CompactionPipeline.replaceAtIndex}} which not included in branch-2 patch for HBASE-18375:
> {code:java}
> // the version increment is indeed needed, because the swap uses removeAll() method of the
> // linked-list that compares the objects to find what to remove.
> // The flattening changes the segment object completely (creation pattern) and so
> // swap will not proceed correctly after concurrent flattening.
> version++;
> {code}
>
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