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https://issues.apache.org/jira/browse/CASSANDRA-6477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13955394#comment-13955394
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Jeremiah Jordan commented on CASSANDRA-6477:
--------------------------------------------

bq. I may be being dim here, but it seems to me that with this scheme you would 
need to write a reverse record of 25, user1->replaced 24, so when you lookup on 
25, you can then read 24 and check there were no competing updates? Either that 
or read the original record, which sort of defeats the point of 
denormalisation...

No, you resolve it in compaction or on lookup of "24".  Compaction sees the two 
different tombstones for 24 and then resolves them to the correct new value, 
deleting the wrong new value.  Or a look up of "24" pulls in the two 
tombstones, resolves them to the correct one, deletes the wrong one, and 
returns none to the user.

> Partitioned indexes
> -------------------
>
>                 Key: CASSANDRA-6477
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6477
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: API, Core
>            Reporter: Jonathan Ellis
>             Fix For: 3.0
>
>
> Local indexes are suitable for low-cardinality data, where spreading the 
> index across the cluster is a Good Thing.  However, for high-cardinality 
> data, local indexes require querying most nodes in the cluster even if only a 
> handful of rows is returned.



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