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https://issues.apache.org/jira/browse/HBASE-22623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16904119#comment-16904119
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stack edited comment on HBASE-22623 at 8/9/19 7:28 PM:
-------------------------------------------------------

bq. "...but what I'm trying to understand is why. "

Because we were afraid to expose this fundamental for others to manipulate. 
WALEdit shows up in a bunch of contexts. There is the original write to the 
WAL; there is the WAL Replay; and there is replication-time. Any mis-accounting 
of Cells or sizes would mess us up. Debugging a cluster with missing or 
mis-accounted edits is a time sink. We were being conservative.



A few more notes:

 * I'm late to the party. Sorry. Duo raises points I would have (but does a 
better job making his point). Anoop notes that there are inconsistencies in our 
CP API which come to light because Geoffrey has brought the spotlight; that is 
no surprise. Lets file issues at least for now while iron is hot.
 * This is a really good discussion.


was (Author: stack):
bq. "...but what I'm trying to understand is why. "

Because we were afraid to expose this fundamental for others to manipulate. 
WALEdit shows up in a bunch of contexts. There is the original write to the 
WAL; there is the WAL Replay; and there is replication-time. Any mis-accounting 
of Cells or sizes would mess us up. Debugging a cluster with missing or 
mis-accounted edits is a time sink. We were being conservative.



A few more notes:

 * I'm late to the party. Sorry. Duo raises points I would have. Anoop notes 
that there are inconsistencies in our CP API which come to light because 
Geoffrey has brought the spotlight. There is no surprise here.
 * This is a really good discussion.

> 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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