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https://issues.apache.org/jira/browse/HBASE-15716?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15721718#comment-15721718
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binlijin commented on HBASE-15716:
----------------------------------
Looks like we can not use the patch for master version now?
Mvcc read point is not always advancing.
{code}
// synchronize on scannerReadPoints so that nobody calculates
// getSmallestReadPoint, before scannerReadPoints is updated.
IsolationLevel isolationLevel = scan.getIsolationLevel();
long mvccReadPoint = PackagePrivateFieldAccessor.getMvccReadPoint(scan);
synchronized (scannerReadPoints) {
if (mvccReadPoint > 0) {
this.readPt = mvccReadPoint;
} else if (nonce == HConstants.NO_NONCE || rsServices == null
|| rsServices.getNonceManager() == null) {
this.readPt = getReadPoint(isolationLevel);
} else {
this.readPt =
rsServices.getNonceManager().getMvccFromOperationContext(nonceGroup, nonce);
}
scannerReadPoints.put(this, this.readPt);
}
{code}
> HRegion#RegionScannerImpl scannerReadPoints synchronization constrains random
> read
> ----------------------------------------------------------------------------------
>
> Key: HBASE-15716
> URL: https://issues.apache.org/jira/browse/HBASE-15716
> Project: HBase
> Issue Type: Bug
> Components: Performance
> Reporter: stack
> Assignee: stack
> Attachments:
> 15716.implementation.using.ScannerReadPoints.branch-1.patch,
> 15716.prune.synchronizations.patch, 15716.prune.synchronizations.v3.patch,
> 15716.prune.synchronizations.v4.patch, 15716.prune.synchronizations.v4.patch,
> 15716.wip.more_to_be_done.patch, HBASE-15716.branch-1.001.patch,
> HBASE-15716.branch-1.002.patch, HBASE-15716.branch-1.003.patch,
> HBASE-15716.branch-1.004.patch, HBASE-15716.branch-1.005.patch,
> ScannerReadPoints.java, ScannerReadPoints.v2.java, Screen Shot 2016-04-26 at
> 2.05.45 PM.png, Screen Shot 2016-04-26 at 2.06.14 PM.png, Screen Shot
> 2016-04-26 at 2.07.06 PM.png, Screen Shot 2016-04-26 at 2.25.26 PM.png,
> Screen Shot 2016-04-26 at 6.02.29 PM.png, Screen Shot 2016-04-27 at 9.49.35
> AM.png, Screen Shot 2016-06-30 at 9.52.52 PM.png, Screen Shot 2016-06-30 at
> 9.54.08 PM.png, TestScannerReadPointDoesntGoBack.java,
> TestScannerReadPoints.java, before_after.png,
> current-branch-1.vs.NoSynchronization.vs.Patch.png, hits.png,
> remove.locks.patch, remove_cslm.patch
>
>
> Here is a [~lhofhansl] special.
> When we construct the region scanner, we get our read point and then store it
> with the scanner instance in a Region scoped CSLM. This is done under a
> synchronize on the CSLM.
> This synchronize on a region-scoped Map creating region scanners is the
> outstanding point of lock contention according to flight recorder (My work
> load is workload c, random reads).
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