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https://issues.apache.org/jira/browse/HBASE-10502?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13898132#comment-13898132
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Liyin Tang commented on HBASE-10502:
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Actually HBase-9272 + HBase10502 is quite effective to optimize Join queries.
Assuming a join query such as Table A joins Table B based on row key / some
prefix, then HBase-9272 is useful to issue the initial scan in parallel to
retrieve all the join keys, and then based on join keys, multiple scan queries
for Table B can be constructed and be submitted in parallel by HBase10502.
> [89-fb] ParallelScanner: a client utility to perform multiple scan requests
> in parallel.
> ----------------------------------------------------------------------------------------
>
> Key: HBASE-10502
> URL: https://issues.apache.org/jira/browse/HBASE-10502
> Project: HBase
> Issue Type: New Feature
> Reporter: Liyin Tang
> Fix For: 0.89-fb
>
>
> ParallelScanner is a utility class for the HBase client to perform multiple
> scan requests in parallel. It requires all the scan requests having the same
> caching size for the simplicity purpose.
>
> This class provides 3 very basic functionalities:
> * The initialize function will Initialize all the ResultScanners by calling
> {@link HTable#getScanner(Scan)} in parallel for each scan request.
> * The next function will call the corresponding {@link ResultScanner#next(int
> numRows)} from each scan request in parallel, and then return all the results
> together as a list. Also, if result list is empty, it indicates there is no
> data left for all the scanners and the user can call {@link #close()}
> afterwards.
> * The close function will close all the scanners and shutdown the thread pool.
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