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https://issues.apache.org/jira/browse/FLINK-10470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16633712#comment-16633712
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ASF GitHub Bot commented on FLINK-10470:
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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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