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https://issues.apache.org/jira/browse/HBASE-18747?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16203316#comment-16203316
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Duo Zhang commented on HBASE-18747:
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{quote}
This preFlush hook some way same as postFlushScannerOpen . correct?
{quote}
Yes.
{quote}
Dont know why we did not go the same way of pre/post hooks.
{quote}
I think in the past we want users to create a StoreScanner in the CP hooks and
in preFlush/preCompact we already have the scanner so we introduce the
preXXXScannerOpen method.
And there is also a preStoreScannerOpen hook which is a hook on the normal read
path. You can see NoOpScanPolicyObserver to see the usage.
Thanks.
> Introduce new example and helper classes to tell CP users how to do filtering
> on scanners
> -----------------------------------------------------------------------------------------
>
> Key: HBASE-18747
> URL: https://issues.apache.org/jira/browse/HBASE-18747
> Project: HBase
> Issue Type: Sub-task
> Components: Coprocessors
> Reporter: Duo Zhang
> Assignee: Duo Zhang
> Priority: Critical
> Fix For: 2.0.0-alpha-4
>
> Attachments: HBASE-18747.patch
>
>
> Finally we decided that CP users should not have the ability to create
> {{StoreScanner}} or {{StoreFileScanner}}, so it is impossible for them to
> filter out some cells when flush or compaction by simply provide a filter
> when constructing {{StoreScanner}}.
> But I think filtering out some cells is a very important usage for CP users,
> so we need to provide the ability in another way. Theoretically it can be
> done with wrapping an {{InternalScanner}}, but I think we need to give an
> example, or even some helper classes to help CP users.
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