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Posted to mapreduce-issues@hadoop.apache.org by "Xiaoming Shi (JIRA)" <ji...@apache.org> on 2011/03/13 04:16:27 UTC
[jira] Created: (MAPREDUCE-2380) Multiple replace function call can
be replaced with a single for loop to improve performance
Multiple replace function call can be replaced with a single for loop to improve performance
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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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