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Posted to mapreduce-issues@hadoop.apache.org by "Thiago Pinto (JIRA)" <ji...@apache.org> on 2016/05/13 23:12:13 UTC
[jira] [Commented] (MAPREDUCE-2380) Multiple replace function call
can be replaced with a single for loop to improve performance
[ 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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