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https://issues.apache.org/jira/browse/HBASE-4999?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrew Purtell resolved HBASE-4999.
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Resolution: Incomplete
> Constraints - Enhance checkAndPut to do atomic arbitrary constraint checks
> --------------------------------------------------------------------------
>
> Key: HBASE-4999
> URL: https://issues.apache.org/jira/browse/HBASE-4999
> Project: HBase
> Issue Type: Improvement
> Components: Client, Coprocessors
> Reporter: Suraj Varma
> Labels: CAS, checkAndPut, constraints
>
> Related work: HBASE-4605
> It would be great if checkAndPut (CAS) can be enhanced to not just use a
> value comparison as a gating factor for the put, but rather have the
> capability of doing arbitrary constraint checks on the column value (where
> the current comparinator approach is a subset of possible constraints that
> can be checked). Commonly used constraints (like comparisons) can be provided
> out of the box and we should have the ability to accept custom constraints
> set by the client for the checkAndPut call.
> One use-case would be the ability to implement something like the below in
> HBase.
> Pseudo sql:
> update table-name
> set column-name = new-value
> where (column-value - new-value) > threshold-value
> ... where the mutation would go through only if the specified constraint in
> the where clause is true.
> Current options include using a co-processor to do
> preCheckAndPut/postCheckAndPut constraint checks - but this is not atomic.
> i.e. the row lock needs to be released by the co-processor before the real
> checkAndPut call, thus not meeting the atomic requirement.
> Everything above is still meant to be at row level (so, no cross-row
> constraint checking is implied here).
> And ideal end result would be that an HBase client would be able to specify a
> set of constraints on multiple column qualifiers as part of the checkAndPut
> call. The call goes through if all the constraints are satisfied or doesn't
> if any of the constraints fail. And the above checkAndPut should be
> atomically executed (just like current checkAndPut semantics).
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