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https://issues.apache.org/jira/browse/HBASE-22622?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16873519#comment-16873519
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Geoffrey Jacoby commented on HBASE-22622:
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[~Apache9] - like a view in a relational database, each view is associated with
a fixed query against a parent table or view. So in the FOO.BAR example above,
if BAR is a view, it might have a query of "SELECT * FROM FOO.PARENT WHERE
KeyColumn = '123'"
Then if the user says " SELECT * FROM FOO.BAR WHERE KeyColumn2 = '456' ",
Phoenix knows to create a Scan that's the equivalent of "SELECT * FROM
FOO.PARENT WHERE KeyColumn = '123' AND KeyColumn2 = '456'.
While a view can have another view as a parent, at some point in the chain
there will be a table that maps 1:1 to an HBase table. So now we have a Scan
with both the appropriate table, projected columns, and Filters. A similar
thing happens on UPSERTs to create appropriate Puts and on DELETE statements to
create HBase Deletes.
> WALKey Extended Attributes
> --------------------------
>
> Key: HBASE-22622
> URL: https://issues.apache.org/jira/browse/HBASE-22622
> Project: HBase
> Issue Type: New Feature
> Components: wal
> Reporter: Geoffrey Jacoby
> Assignee: Geoffrey Jacoby
> Priority: Major
>
> It would be useful if the WAL protobuf and WALKey class included an optional
> map of extended key/value attributes that downstream coprocessors could use
> to annotate WAL Entries. While standard HBase replication would not use them,
> custom replication endpoints could use the data to make filtering decisions
> or take actions.
> An example use case would be allowing a tool like Phoenix to annotate
> WAL.Entries to indicate that a given Entry is associated with a particular
> Phoenix view rather than the base Phoenix table. (Multiple logical views in
> Phoenix can map to the same physical HBase table.) A custom replication
> endpoint might choose to replicate some views but not others.
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