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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-19001) Remove the hooks in RegionObserver which are designed to construct a StoreScanner which is marked as IA.Private
Date Tue, 17 Oct 2017 13:08:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-19001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16207615#comment-16207615

Anoop Sam John commented on HBASE-19001:

Am +1
Pls mention abt the removal of method from Region in the Release Notes also.
So you already proposed a solution for the Tephra usage?
bq.I think the first one is not a problem for flush/compaction, we always read all versions
when flush/compaction.
In the wrapper outer scanner, we will get all the Cells (even which might get removed by SQM
logics). I think so. Pls verify?  We already have this use case in the Examples module I believe.

> Remove the hooks in RegionObserver which are designed to construct a StoreScanner which
is marked as IA.Private
> ---------------------------------------------------------------------------------------------------------------
>                 Key: HBASE-19001
>                 URL: https://issues.apache.org/jira/browse/HBASE-19001
>             Project: HBase
>          Issue Type: Sub-task
>          Components: Coprocessors
>            Reporter: Duo Zhang
>            Assignee: Duo Zhang
>             Fix For: 2.0.0-alpha-4
>         Attachments: HBASE-19001-v1.patch, HBASE-19001.patch
> There are three methods here
> {code}
> KeyValueScanner preStoreScannerOpen(ObserverContext<RegionCoprocessorEnvironment>
>       Store store, Scan scan, NavigableSet<byte[]> targetCols, KeyValueScanner
s, long readPt)
>       throws IOException;
> InternalScanner preFlushScannerOpen(ObserverContext<RegionCoprocessorEnvironment>
>       Store store, List<KeyValueScanner> scanners, InternalScanner s, long readPoint)
>       throws IOException;
> InternalScanner preCompactScannerOpen(ObserverContext<RegionCoprocessorEnvironment>
>       Store store, List<? extends KeyValueScanner> scanners, ScanType scanType,
long earliestPutTs,
>       InternalScanner s, CompactionLifeCycleTracker tracker, CompactionRequest request,
>       long readPoint) throws IOException;
> {code}
> For the flush and compact ones, we've discussed many times, it is not safe to let user
inject a Filter or even implement their own InternalScanner using the store file scanners,
as our correctness highly depends on the complicated logic in SQM and StoreScanner. CP users
are expected to wrap the original InternalScanner(it is a StoreScanner anyway) in preFlush/preCompact
methods to do filtering or something else.
> For preStoreScannerOpen it even returns a KeyValueScanner which is marked as IA.Private...
This is less hurt but still, we've decided to not expose StoreScanner to CP users so here
this method is useless. CP users can use preGetOp and preScannerOpen method to modify the
Get/Scan object passed in to inject into the scan operation.

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