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https://issues.apache.org/jira/browse/PIG-965?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ankit Modi updated PIG-965:
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Attachment: poregex2.patch
poregex.patch
These are patches for two implementations
One (poregex.patch) is an implementation applying optimization mentioned above
in the JIRA.
Second (poregex2.patch) implementation applies optimization 1 and uses
dk.brics.automaton for running simple regular expressions. Otherwise it reverts
back to java.util.regex.
In 1 the decision to use optimization two or use java.util.regex is decided by
getSimpleString method
In 2 the decision to use dk.brics.automaton is done by
determineBestRegexMethod. ( changes to build.xml is this patch are temporary )
Both patches use RegexInit as an implementation which makes a decision (
calling the above mentioned decision functions ) and then sets the
implementation to one decided by the decision function.
In second patch, the decision function was created looking at the support of
operators in dk.brics.automaton and its grammar. I tried out the classes
supported and not supported in dk.brics.automaton and decided upon it.
I could not find any specific page mentioning the difference between regex
language java.util.regex and dk.brics.automaton.
> 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: poregex.patch, 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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