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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6066) some low hanging read path improvement ideas
Date Wed, 16 Jan 2013 02:38:14 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6066?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13554679#comment-13554679
] 

Hadoop QA commented on HBASE-6066:
----------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12565053/6066-rebased-1.patch
  against trunk revision .

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

    {color:red}-1 tests included{color}.  The patch doesn't appear to include any new or modified
tests.
                        Please justify why no new tests are needed for this patch.
                        Also please list what manual steps were performed to verify this patch.

    {color:green}+1 hadoop2.0{color}.  The patch compiles against the hadoop 2.0 profile.

    {color:green}+1 javadoc{color}.  The javadoc tool did not generate any warning messages.

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

    {color:red}-1 findbugs{color}.  The patch appears to introduce 2 new Findbugs (version
1.3.9) 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:red}-1 core tests{color}.  The patch failed these unit tests:
                       org.apache.hadoop.hbase.regionserver.TestJoinedScanners

Test results: https://builds.apache.org/job/PreCommit-HBASE-Build/4037//testReport/
Findbugs warnings: https://builds.apache.org/job/PreCommit-HBASE-Build/4037//artifact/trunk/patchprocess/newPatchFindbugsWarningshbase-hadoop2-compat.html
Findbugs warnings: https://builds.apache.org/job/PreCommit-HBASE-Build/4037//artifact/trunk/patchprocess/newPatchFindbugsWarningshbase-common.html
Findbugs warnings: https://builds.apache.org/job/PreCommit-HBASE-Build/4037//artifact/trunk/patchprocess/newPatchFindbugsWarningshbase-protocol.html
Findbugs warnings: https://builds.apache.org/job/PreCommit-HBASE-Build/4037//artifact/trunk/patchprocess/newPatchFindbugsWarningshbase-server.html
Findbugs warnings: https://builds.apache.org/job/PreCommit-HBASE-Build/4037//artifact/trunk/patchprocess/newPatchFindbugsWarningshbase-hadoop1-compat.html
Findbugs warnings: https://builds.apache.org/job/PreCommit-HBASE-Build/4037//artifact/trunk/patchprocess/newPatchFindbugsWarningshbase-examples.html
Findbugs warnings: https://builds.apache.org/job/PreCommit-HBASE-Build/4037//artifact/trunk/patchprocess/newPatchFindbugsWarningshbase-hadoop-compat.html
Console output: https://builds.apache.org/job/PreCommit-HBASE-Build/4037//console

This message is automatically generated.
                
> some low hanging read path improvement ideas 
> ---------------------------------------------
>
>                 Key: HBASE-6066
>                 URL: https://issues.apache.org/jira/browse/HBASE-6066
>             Project: HBase
>          Issue Type: Sub-task
>          Components: Performance
>            Reporter: Kannan Muthukkaruppan
>            Assignee: Michal Gregorczyk
>            Priority: Critical
>              Labels: noob
>             Fix For: 0.96.0
>
>         Attachments: 0001-jira-HBASE-6066-89-fb-Some-read-performance-improvem.patch,
6066-rebased-1.patch, metric-stringbuilder-fix.patch
>
>
> I was running some single threaded scan performance tests for a table with small sized
rows that is fully cached. Some observations...
> We seem to be doing several wasteful iterations over and/or building of temporary lists.
> 1) One such is the following code in HRegionServer.next():
> {code}
>    boolean moreRows = s.next(values, HRegion.METRIC_NEXTSIZE);
>    if (!values.isEmpty()) {
>      for (KeyValue kv : values) {              ------> #### wasteful in most cases
>        currentScanResultSize += kv.heapSize();
>    }
>    results.add(new Result(values));
> {code}
> By default the "maxScannerResultSize" is Long.MAX_VALUE. In those cases,
> we can avoid the unnecessary iteration to compute currentScanResultSize.
> 2) An example of a wasteful temporary array, is "results" in
> RegionScanner.next().
> {code}
>       results.clear();
>       boolean returnResult = nextInternal(limit, metric);
>       outResults.addAll(results);
> {code}
> results then gets copied over to outResults via an addAll(). Not sure why we can not
directly collect the results in outResults.
> 3) Another almost similar exmaple of a wasteful array is "results" in StoreScanner.next(),
which eventually also copies its results into "outResults".
> 4) Reduce overhead of "size metric" maintained in StoreScanner.next().
> {code}
>   if (metric != null) {
>      HRegion.incrNumericMetric(this.metricNamePrefix + metric,
>                                copyKv.getLength());
>   }
>   results.add(copyKv);
> {code}
> A single call to next() might fetch a lot of KVs. We can first add up the size of those
KVs in a local variable and then in a finally clause increment the metric one shot, rather
than updating AtomicLongs for each KV.
> 5) RegionScanner.next() calls a helper RegionScanner.next() on the same object. Both
are synchronized methods. Synchronized methods calling nested synchronized methods on the
same object are probably adding some small overhead. The inner next() calls isFilterDone()
which is a also a synchronized method. We should factor the code to avoid these nested synchronized
methods.

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