[
https://issues.apache.org/jira/browse/HBASE-17434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15811590#comment-15811590
]
Eshcar Hillel commented on HBASE-17434:
---------------------------------------
The logic and timing of moving segments into the pipeline and out of it is done
by CompactingMemStore.
CompactingMemStore maintains two invariants/conditions:
(1) not to remove a segment before it is added to the next entity in the
active-pipeline-snapshot chain
(2) when creating the scanners for the memstore create them in the same order
as the data flows, namely active then pipeline then snapshot.
With these two invariants we are guaranteed not to skip any data in a get or
scan operation but may scan the same segment twice.
If and when getScanners() is added to CompactionPipeline then it needs to
follow the guidelines in the documentation: get a local copy of the
readOnlyCopy and create scanners for the local copy.
> 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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
