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https://issues.apache.org/jira/browse/HBASE-17434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15811748#comment-15811748
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Anastasia Braginsky commented on HBASE-17434:
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According to DefaultMemStore this is how the snapshot() is working there:
Line 1: this.snapshot = active;
Line 2: resetActive();
and this is how getScanners() is working there:
Line 3: list.add(this.active.getScanner(readPt, 1));
Line 4: list.addAll(this.snapshot.getScanners(readPt, 0));
This is how the code worked before we did anything.
So also here there is a moment between two lines (1 and 2) that if scanners are
taken then, the active will appear twice. So we didn't add nothing new here.
> New Synchronization Scheme for Compaction Pipeline
> --------------------------------------------------
>
> Key: HBASE-17434
> URL: https://issues.apache.org/jira/browse/HBASE-17434
> Project: HBase
> Issue Type: Bug
> Reporter: Eshcar Hillel
> Assignee: Eshcar Hillel
> Attachments: HBASE-17434-V01.patch, HBASE-17434-V02.patch,
> HBASE-17434-V03.patch
>
>
> A new copyOnWrite synchronization scheme is introduced for the compaction
> pipeline.
> The new scheme is better since it removes the lock from getSegments() which
> is invoked in every get and scan operation, and it reduces the number of
> LinkedList objects that are created at runtime, thus can reduce GC (not by
> much, but still...).
> In addition, it fixes the method getTailSize() in compaction pipeline. This
> method creates a MemstoreSize object which comprises the data size and the
> overhead size of the segment and needs to be atomic.
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