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https://issues.apache.org/jira/browse/HBASE-24321?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17099438#comment-17099438
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Duo Zhang commented on HBASE-24321:
-----------------------------------
Reading the comment of ScanOptions, the intenion here is that, for complicated
scan logic for compaction/flush, you should wrapper the InternalScanner? You
can see the WriteHeavyIncrementObserver in hbase-examples module for more
details.
> Add writable MinVersions and read-only Scan to coproc ScanOptions
> -----------------------------------------------------------------
>
> Key: HBASE-24321
> URL: https://issues.apache.org/jira/browse/HBASE-24321
> Project: HBase
> Issue Type: Improvement
> Reporter: Geoffrey Jacoby
> Assignee: Geoffrey Jacoby
> Priority: Major
> Fix For: 2.3.0
>
>
> Between HBase 1.x and 2.0, the RegionObserver pre*ScannerOpen coprocessors
> were significantly changed so that the coproc implementer no longer has
> access to the actual Scanner, just a ScanOptions object that can be changed
> in limited ways. This is safer and prevents resource leaks and other bugs.
> While ScanOptions provides support for changing TTL, KeepDeletedCells, and
> MaxVersions, a fourth column family config parameter, MinVersions, appears to
> have been missed. This prevents coproc implementers from changing MinVersions
> dynamically. An example of this is PHOENIX-5645, which in the forthcoming
> Phoenix 4.16 (based on HBase 1.x) will allow users to configure a moving
> window where all versions are kept, and thus point-in-time queries are safe.
> This cannot be put in the forthcoming Phoenix 5.1 (based on HBase 2.1 and
> 2.2) because of the coproc changes.
> Relatedly, preStoreScannerOpen lacks access to the Scan in HBase 2.0 and up.
> This prevents coprocs from reading the Scan parameters to check if, for
> example, a Scan has set the max time to a point in the past, and thus needs
> to override KeepDeletedCells. This can lead to incorrect behavior when doing
> point-in-time queries or using transactional engines that treat physically
> committed HBase writes as logically uncommitted parts of a transaction. It's
> also a correctness problem for PHOENIX-5645. Please note that only
> _read-only_ access to the Scan from the store scanner coproc hook is in scope
> for this change.
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