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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-2126) Improving performance of merge sort by multi-threaded implementation
Date Fri, 17 Jul 2015 22:45:04 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-2126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14632060#comment-14632060
] 

Hadoop QA commented on PHOENIX-2126:
------------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12745904/PHOENIX-2126_v1.0.patch
  against master branch at commit f006df5451859eb9d22130bb46b58460eee49674.
  ATTACHMENT ID: 12745904

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

    {color:green}+1 tests included{color}.  The patch appears to include 3 new or modified
tests.

    {color:red}-1 patch{color}.  The patch command could not apply the patch.

Console output: https://builds.apache.org/job/PreCommit-PHOENIX-Build/122//console

This message is automatically generated.

> Improving performance of merge sort by multi-threaded implementation
> --------------------------------------------------------------------
>
>                 Key: PHOENIX-2126
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-2126
>             Project: Phoenix
>          Issue Type: Improvement
>    Affects Versions: 4.1.0, 4.2.0
>            Reporter: Ankit Singhal
>         Attachments: PHOENIX-2126_v1.0.patch
>
>
> {code}
> CREATE TABLE IF NOT EXISTS DSP_VIEW_DAILY1 (
> dim1 INTEGER NOT NULL,
> A.B INTEGER,
> A.M DECIMAL,
> CONSTRAINT PK PRIMARY KEY
> (dim1))
> SALT_BUCKETS =256,DEFAULT_COLUMN_FAMILY='A';
> {code}
> *Query to benchmark:-*
> {code}
> select dim1,sum(b),sum(m) from table where Datemth>=201505 and Datemth<=201505
and dim1 IS NOT NULL  group by dim1 order by sum(m) desc nulls last limit 10;
> {code}
> *current scenario:-*
> *CASE 1: * consider the case when dim1 is high cardinality attribute (10K+) and table
have salt bucket set to 256, we will get 256 iterators from above query at the client and
MergeSortRowKeyResultIterator has to merge these 256 iterators with single thread. So let's
say each iterator has 10k tuples returned, then merge sort needs to merge 2.5M tuples which
will be costly if it is done with single thread and the query spend most of its time on client
> *CASE 2: * consider the case when dim1 is high cardinality attribute (10K+) and table
have salt bucket set to 1, we will get 1 iterator from  above query at the client and MergeSortRowKeyResultIterator
doesn't need to merge anything. Here, it is fine with single thread.
> *CASE 3: * consider the case when dim1 is low cardinality attribute (10-100) and table
have salt bucket set to 256, we will get 256 iterator from  above query at the client and
MergeSortRowKeyResultIterator has to merge these 256 iterators with single thread. here the
single thread is also fine as he has to merge only 2560 tuples.
> *Solution for case1 problem is:-*
> Optimized the implementation of merging 'n'-sorted iterators(having 'm' tuples)  by using
"min heap" which optimizes the time complexity from 
> O(n2m) to O(nmLogn) (as heapify takes (Logn) time).
> And, By using multiple-threads('t') to process group of iterators which further optimized
the complexity to 
> T(nm)=T(nm)/t+T(t)



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