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From "Thiago Pinto (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-2380) Multiple replace function call can be replaced with a single for loop to improve performance
Date Fri, 13 May 2016 23:12:13 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2380?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15283290#comment-15283290
] 

Thiago Pinto commented on MAPREDUCE-2380:
-----------------------------------------

Duplicated issue.

> Multiple replace function call can be replaced with a single for loop to improve performance

> ---------------------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-2380
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2380
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: tools/rumen
>    Affects Versions: 0.21.0
>            Reporter: Xiaoming Shi
>
> {noformat}
> ./hadoop-0.21.0/mapred/src/tools/org/apache/hadoop/tools/rumen/LoggedTaskAttempt.java
 line:362
> ./chukwa-0.4.0/src/java/org/apache/hadoop/chukwa/datacollection/writer/localfs/LocalWriter.java
  line:249
> {noformat}
> 4 consecutive replace() is called to remove the special characters.  It's 3+ times slower
than using a for loop 
> replace them all.
> {noformat}
> e.g.
>  - str.replace('a', '#');
>  - str.replace('b', '%');
>  + StringBuilder sb = new StringBuilder( str.length() );
>  + for (int i=0; i < str.length(); i++)
>  +  {
>  +           char c = str.charAt(i);
>  +         if ( c == 'a' )
>  +               sb.append('#');
>  +       else if ( c== 'b' )
>  +               sb.append('%');
>  +       else 
>  +              sb.append(c); 
>  +  }
>  +  str  = sb.toString();
> {noformat}
> This bug has the same problem as the MySQL bug : http://bugs.mysql.com/bug.php?id=45699



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