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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-10470) Add method to check if pattern can produce empty matches
Date Mon, 01 Oct 2018 08:32:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-10470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16633712#comment-16633712
] 

ASF GitHub Bot commented on FLINK-10470:
----------------------------------------

dawidwys opened a new pull request #6781: [FLINK-10470] Add method to check if pattern can
produce empty matches
URL: https://github.com/apache/flink/pull/6781
 
 
   ## What is the purpose of the change
   
   This change introduces a method that allows checking if a Pattern can produce empty matches.
It is needed to disable such patterns in MATCH_RECOGNIZE, until we are able to provide a full
support of empty matches in CEP (with proper support of reluctant and greedy)
   
   ## Does this pull request potentially affect one of the following parts:
   
     - Dependencies (does it add or upgrade a dependency): (yes / **no**)
     - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: (yes
/ **no**)
     - The serializers: (yes / **no** / don't know)
     - The runtime per-record code paths (performance sensitive): (yes / **no** / don't know)
     - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing,
Yarn/Mesos, ZooKeeper: (yes / **no** / don't know)
     - The S3 file system connector: (yes / **no** / don't know)
   
   ## Documentation
   
     - Does this pull request introduce a new feature? (yes / **no**)
     - If yes, how is the feature documented? (**not applicable** / docs / JavaDocs / not
documented)
   

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> Add method to check if pattern can produce empty matches
> --------------------------------------------------------
>
>                 Key: FLINK-10470
>                 URL: https://issues.apache.org/jira/browse/FLINK-10470
>             Project: Flink
>          Issue Type: Sub-task
>          Components: CEP
>            Reporter: Dawid Wysakowicz
>            Assignee: Dawid Wysakowicz
>            Priority: Major
>              Labels: pull-request-available
>
> There is couple of inconsistencies how CEP library handles greedy and reluctant operators
at the beginning at end of pattern. This results in subtle problems how empty matches should
be generated for patterns like e.g. A? or A*?, where one is greedy and the other one is reluctant.
In order to provide first version of MATCH_RECOGNIZE function we should have a possibility
to disable patterns which can produce empty matches.



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