[jira] [Commented] (HBASE-24321) Add writable MinVersions and read-only Scan to coproc ScanOptions

["Geoffrey Jacoby (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-24321?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17099273#comment-17099273 ] 

Geoffrey Jacoby commented on HBASE-24321:
-----------------------------------------

My current plan is to add the following to ScanOptions:

* int getMinVersions()
* void setMinVersions(int)
* Scan getScan(), which returns a read-only copy of the Scan. 

Putting everything on ScanOptions avoids the need to change any coprocessor hook interfaces. 

> 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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