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https://issues.apache.org/jira/browse/HBASE-13378?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14573464#comment-14573464
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Enis Soztutar commented on HBASE-13378:
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bq. I'd be ok with this change in 0.98 with a release note describing the
change in semantics. In either case the user is asking for increased possible
concurrency in exchange for 'dirty' reads. What this patch does is alter a bit
how dirty is dirty, depending. (smile) I'm not sure what Enis Soztutar or Nick
Dimiduk would want to do wrt. 1.0 and 1.1, or Sean Busbey for 1.2.
I would put this in the "not a bug fix" bucket, and would not include in 1.0
and 1.1 release lines.
> RegionScannerImpl synchronized for READ_UNCOMMITTED Isolation Levels
> --------------------------------------------------------------------
>
> Key: HBASE-13378
> URL: https://issues.apache.org/jira/browse/HBASE-13378
> Project: HBase
> Issue Type: New Feature
> Reporter: John Leach
> Assignee: John Leach
> Priority: Minor
> Attachments: HBASE-13378.patch, HBASE-13378.txt
>
> Original Estimate: 2h
> Time Spent: 2h
> Remaining Estimate: 0h
>
> This block of code below coupled with the close method could be changed so
> that READ_UNCOMMITTED does not synchronize.
> {CODE:JAVA}
> // synchronize on scannerReadPoints so that nobody calculates
> // getSmallestReadPoint, before scannerReadPoints is updated.
> IsolationLevel isolationLevel = scan.getIsolationLevel();
> synchronized(scannerReadPoints) {
> this.readPt = getReadpoint(isolationLevel);
> scannerReadPoints.put(this, this.readPt);
> }
> {CODE}
> This hotspots for me under heavy get requests.
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