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https://issues.apache.org/jira/browse/HBASE-22623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16902608#comment-16902608
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Geoffrey Jacoby commented on HBASE-22623:
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1. There does not appear to be a preWALWrite in RegionObserver that I can see
in master, and I don't see it called in doWALAppend. If I'm missing something,
please let me know -- figuring out the hooks and their ordering isn't
well-documented. The coprocessor hook needs to be in RegionObserver along with
all the other mutation-related coprocessor hooks, because of shared context.
2. For my particular use case, annotating the WALKey as provided in HBASE-22622
is sufficient. [~apurtell] pointed out during the review that other use cases
might have need of the edit, and that it would be trivial to add it now rather
than need a breaking change later, which I agree with.
(3). In the hypothetical, no-longer-relevant case where you added extra Cells
to the WALEdit but not the MemStore, you would presumably have the replication
endpoint that consumed them filter them out from being replicated to the remote
peer cluster. The are Cell-level filtering APIs in the replication code.
> Add RegionObserver coprocessor hook for preWALAppend
> ----------------------------------------------------
>
> Key: HBASE-22623
> URL: https://issues.apache.org/jira/browse/HBASE-22623
> Project: HBase
> Issue Type: New Feature
> Reporter: Geoffrey Jacoby
> Assignee: Geoffrey Jacoby
> Priority: Major
> Fix For: 3.0.0, 1.5.0, 2.3.0
>
>
> While many coprocessor hooks expose the WALEdit to implementing coprocs,
> there aren't any that expose the WALKey before it's created and added to the
> WALEntry.
> It's sometimes useful for coprocessors to be able to edit the WALKey, for
> example to add extended attributes using the fields to be added in
> HBASE-22622.
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