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https://issues.apache.org/jira/browse/PHOENIX-4552?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16655995#comment-16655995
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Stephen Petschulat commented on PHOENIX-4552:
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Compaction is probably the biggest benefit. Yes, we could do without mutable
secondary index in that case. The idea is we'd set it based on wall clock and
record that as a "change set id". Since it is always increasing (we'd take care
of race conditions) it would then be possible for the client to query for all
of the most recent changes.
That, combined with max versions = 3 would allow change history to be compacted
by hbase quite efficiently. Our particular use cases only requires the client
either query the entire dataset (most recent versions of all data) or else the
most recent change set. The three versions helps ensure "the most recent change
set" stays around long enough for a query client that might take many minutes
to run.
Obviously if our changes come in faster than our longest running query we'd
risk a particular change set getting compacted by HBase, but we're ok with
throttling the update rate and/or tuning the number of versions stored.
> Allow ROW_TIMESTAMP declaration for non PK column
> -------------------------------------------------
>
> Key: PHOENIX-4552
> URL: https://issues.apache.org/jira/browse/PHOENIX-4552
> Project: Phoenix
> Issue Type: New Feature
> Reporter: Stephen Petschulat
> Priority: Minor
>
> By declaring a ROW_TIMESTAMP constraint on a Phoenix table, it does two
> things 1) expose the hbase native timestamp as this column and 2) prepend
> your primary key with this timestamp as well.
> It would be useful to have a similar feature that only exposes the hbase
> native timestamp. This would allow explicit setting of the timestamp when
> upserting data while allowing multiple hbase versions. It is possible to then
> query for that specific key and version(s).
> Potential approach:
> {code:sql}
> CREATE TABLE COMMENTS (
> COMMENT_ID INT NOT NULL,
> REVISION_NUM BIGINT NOT NULL ROW_TIMESTAMP, // NEW use of keyword
> COMMENT_BODY TEXT
> CONSTRAINT PK PRIMARY KEY(COMMENT_ID))
> UPSERT INTO COMMENTS (123, 1, 'edit 1 comment')
> UPSERT INTO COMMENTS (123, 2, 'edit 2 of comment')
> UPSERT INTO COMMENTS (123, 3, 'edit 3 of comment')
> {code}
>
> Current behavior of ROW_TIMESTAMP would create a new primary for each upsert,
> so querying by primary key is no longer straightforward when you don't know
> the version number at query time.
> {code:sql}
> SELECT * FROM COMMENTS WHERE COMMENT_ID = 123 // => returns most recent
> version 'edit 3 of comment'
> SELECT * FROM COMMENTS WHERE COMMENT_ID = 123 AND REVISION_NUM = 1 // =>
> returns explicit version 'edit 1 comment'
> {code}
>
> It can also be useful to return multiple versions (related: PHOENIX-590)
> {code:sql}
> SELECT * FROM COMMENTS WHERE COMMENT_ID = 123 AND REVISION_NUM < 3 // =>
> returns 2 rows
> {code}
>
> Or just the highest version less than or equal to a particular version
> (allowing snapshot queries):
> {code:sql}
> // set CurrentSCN=2 on connection
> SELECT * FROM COMMENTS WHERE COMMENT_ID = 123 // => returns 'edit 2 of
> comment'
> {code}
> CurrentSCN already allows this type of snapshot query but not against an
> explicitly set timestamp with multiple versions. The primary key injection
> prevents this. The above query would behave similar to:
> {code:java}
> scan 'COMMENTS', {TIMERANGE => [0, <maxversionid+1>]}
> {code}
> This returns the highest versioned value for each key that is less than a
> specified maximum version number.
>
>
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