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https://issues.apache.org/jira/browse/HBASE-13082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15033927#comment-15033927
 ] 

Hadoop QA commented on HBASE-13082:
-----------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest 
attachment 
  http://issues.apache.org/jira/secure/attachment/12775032/HBASE-13082_18.patch
  against master branch at commit 7979ac46cce36f21033f8ed03c8d0dd5fddde005.
  ATTACHMENT ID: 12775032

    {color:green}+1 @author{color}.  The patch does not contain any @author 
tags.

    {color:green}+1 tests included{color}.  The patch appears to include 46 new 
or modified tests.

    {color:green}+1 hadoop versions{color}. The patch compiles with all 
supported hadoop versions (2.4.0 2.4.1 2.5.0 2.5.1 2.5.2 2.6.0 2.6.1 2.7.0 
2.7.1)

    {color:green}+1 javac{color}.  The applied patch does not increase the 
total number of javac compiler warnings.

    {color:green}+1 protoc{color}.  The applied patch does not increase the 
total number of protoc compiler warnings.

    {color:red}-1 javadoc{color}.  The javadoc tool appears to have generated 2 
warning messages.

                {color:red}-1 checkstyle{color}.  The applied patch generated 
new checkstyle errors. Check build console for list of new errors.

    {color:green}+1 findbugs{color}.  The patch does not introduce any  new 
Findbugs (version 2.0.3) warnings.

    {color:green}+1 release audit{color}.  The applied patch does not increase 
the total number of release audit warnings.

    {color:green}+1 lineLengths{color}.  The patch does not introduce lines 
longer than 100

  {color:green}+1 site{color}.  The mvn post-site goal succeeds with this patch.

     {color:red}-1 core tests{color}.  The patch failed these unit tests:
                       org.apache.hadoop.hbase.io.TestHeapSize

Test results: 
https://builds.apache.org/job/PreCommit-HBASE-Build/16717//testReport/
Release Findbugs (version 2.0.3)        warnings: 
https://builds.apache.org/job/PreCommit-HBASE-Build/16717//artifact/patchprocess/newFindbugsWarnings.html
Checkstyle Errors: 
https://builds.apache.org/job/PreCommit-HBASE-Build/16717//artifact/patchprocess/checkstyle-aggregate.html

                Javadoc warnings: 
https://builds.apache.org/job/PreCommit-HBASE-Build/16717//artifact/patchprocess/patchJavadocWarnings.txt
Console output: 
https://builds.apache.org/job/PreCommit-HBASE-Build/16717//console

This message is automatically generated.

> Coarsen StoreScanner locks to RegionScanner
> -------------------------------------------
>
>                 Key: HBASE-13082
>                 URL: https://issues.apache.org/jira/browse/HBASE-13082
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>            Assignee: ramkrishna.s.vasudevan
>         Attachments: 13082-test.txt, 13082-v2.txt, 13082-v3.txt, 
> 13082-v4.txt, 13082.txt, 13082.txt, HBASE-13082.pdf, HBASE-13082_1.pdf, 
> HBASE-13082_12.patch, HBASE-13082_13.patch, HBASE-13082_14.patch, 
> HBASE-13082_15.patch, HBASE-13082_16.patch, HBASE-13082_17.patch, 
> HBASE-13082_18.patch, HBASE-13082_1_WIP.patch, HBASE-13082_2.pdf, 
> HBASE-13082_2_WIP.patch, HBASE-13082_3.patch, HBASE-13082_4.patch, 
> HBASE-13082_9.patch, HBASE-13082_9.patch, HBASE-13082_withoutpatch.jpg, 
> HBASE-13082_withpatch.jpg, LockVsSynchronized.java, gc.png, gc.png, gc.png, 
> hits.png, next.png, next.png
>
>
> Continuing where HBASE-10015 left of.
> We can avoid locking (and memory fencing) inside StoreScanner by deferring to 
> the lock already held by the RegionScanner.
> In tests this shows quite a scan improvement and reduced CPU (the fences make 
> the cores wait for memory fetches).
> There are some drawbacks too:
> * All calls to RegionScanner need to be remain synchronized
> * Implementors of coprocessors need to be diligent in following the locking 
> contract. For example Phoenix does not lock RegionScanner.nextRaw() and 
> required in the documentation (not picking on Phoenix, this one is my fault 
> as I told them it's OK)
> * possible starving of flushes and compaction with heavy read load. 
> RegionScanner operations would keep getting the locks and the 
> flushes/compactions would not be able finalize the set of files.
> I'll have a patch soon.



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