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https://issues.apache.org/jira/browse/PIG-965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12766985#action_12766985
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Thejas M Nair commented on PIG-965:
-----------------------------------
I found another regex library that is supposed to be faster than
java.util.regex . - dk.brics.automaton.RegExp (BSD license, used in apache
nutch). It does not support all features of java regex, but it is a candidate
that can be used for purposes of this patch (common simpler regexes).
It is faster than java regex, but much slower than 'optimization2' (see numbers
in code comments below)
{code}
String prefix = "123";
Pattern p = Pattern.compile("123.*");
RegExp r = new RegExp("123.*");
Automaton a = r.toAutomaton();
while((str = in.readLine()) != null ){
// optimization 1 - takes 30 secs
// if((p.matcher(str).matches()))
// matches++;
//optimization 2 - takes 15 secs
// int len = prefix.length();
// boolean matched = true;
// for(int i=0; i<len; i++){
// if(prefix.charAt(i) != str.charAt(i)){
// matched = false;
// break;
// }
// }
// if(matched)
// matches++;
// dk.brics.automaton - takes 25 secs
// if(a.run(str))
// matches++;
tot++;
}
{code}
> PERFORMANCE: optimize common case in matches (PORegex)
> ------------------------------------------------------
>
> Key: PIG-965
> URL: https://issues.apache.org/jira/browse/PIG-965
> Project: Pig
> Issue Type: Improvement
> Components: impl
> Reporter: Thejas M Nair
>
> Some frequently seen use cases of 'matches' comparison operator have follow
> properties -
> 1. The rhs is a constant string . eg "c1 matches 'abc%' "
> 2. Regexes such that look for matching prefix , suffix etc are very common.
> eg - "abc%', "%abc", '%abc%'
> To optimize for these common cases , PORegex.java can be changed to -
> 1. Compile the pattern (rhs of matches) re-use it if the pattern string has
> not changed.
> 2. Use string comparisons for simple common regexes (in 2 above).
> The implementation of Hive like clause uses similar optimizations.
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