drill-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5879) Optimize "Like" operator
Date Fri, 19 Jan 2018 00:01:00 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16331459#comment-16331459
] 

ASF GitHub Bot commented on DRILL-5879:
---------------------------------------

Github user priteshm commented on the issue:

    https://github.com/apache/drill/pull/1072
  
    @paul-rogers Is this ready for commit?


> Optimize "Like" operator
> ------------------------
>
>                 Key: DRILL-5879
>                 URL: https://issues.apache.org/jira/browse/DRILL-5879
>             Project: Apache Drill
>          Issue Type: Improvement
>          Components: Execution - Relational Operators
>         Environment: * 
>            Reporter: salim achouche
>            Assignee: salim achouche
>            Priority: Minor
>             Fix For: 1.13.0
>
>
> Query: select <column-list> from <table> where colA like '%a%' or colA like
'%xyz%';
> Improvement Opportunities
> # Avoid isAscii computation (full access of the input string) since we're dealing with
the same column twice
> # Optimize the "contains" for-loop 
> Implementation Details
> 1)
> * Added a new integer variable "asciiMode" to the VarCharHolder class
> * The default value is -1 which indicates this info is not known
> * Otherwise this value will be set to either 1 or 0 based on the string being in ASCII
mode or Unicode
> * The execution plan already shares the same VarCharHolder instance for all evaluations
of the same column value
> * The asciiMode will be correctly set during the first LIKE evaluation and will be reused
across other LIKE evaluations
> 2) 
> * The "Contains" LIKE operation is quite expensive as the code needs to access the input
string to perform character based comparisons
> * Created 4 versions of the same for-loop to a) make the loop simpler to optimize (Vectorization)
and b) minimize comparisons
> Benchmarks
> * Lineitem table 100GB
> * Query: select l_returnflag, count(*) from dfs.`<source>` where l_comment not
like '%a%' or l_comment like '%the%' group by l_returnflag
> * Before changes: 33sec
> * After changes    : 27sec



--
This message was sent by Atlassian JIRA
(v7.6.3#76005)

Mime
View raw message