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https://issues.apache.org/jira/browse/PIG-965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12790492#action_12790492
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Thejas M Nair commented on PIG-965:
-----------------------------------
Reviewed the latest patch.
Comments :
* RegexInit.java, in determineBestRegexMethod Line 85 - 120
There are while loops where we are testing only for preceding '\'
The handling of preceding escapes could be done in a separate function, since
the logic is used at multiple places
* RegexInit.java lines 61,147
// This is the case when an old number of escapes
I believe you meant "odd"
* RegexImpl.java - following comments are not relevant anymore
+// LHSXXXX means LHS is constantExpression and RHS varies with each Tuple
+// RHSXXXX means RHS is constantExpression and LHS varies with each Tuple
* NonConstantRegex , line 34-35
{code}
|| rhs.length() != oldString.length()
|| rhs.compareTo(oldString) != 0
{code}
could be simplified as -
{code}
|| !rhs.equals(oldString)
{code}
Did you chose the former because it might be faster ? That can be the case in
this situation, because equals has a additional check of - "instanceOf String"
. So I think the existing code is fine. A comment there might be useful.
Can you also publish your numbers for the comparison of
dk.brics.automaton.RunAutomaton and optimization 2 (Use string comparisons for
simple common regexes ) in the jira ?
> 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
> Assignee: Ankit Modi
> Attachments: automaton.jar, poregex2.patch
>
>
> 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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