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https://issues.apache.org/jira/browse/CASSANDRA-6477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13955527#comment-13955527
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Jeremiah Jordan commented on CASSANDRA-6477:
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[~benedict] two threads update age = null. generate tombstones {{24,
user1->null}}, two of them, so those are OK and not a problem, updated to the
same value, we also need to generate {{null: user1}} as an append to the index.
Then update age=25 generates tombstone {{null, user1->25}} and age=26
generates tombstone {{null, user1->26}}. Those two tombstones will be resolved
on compaction/memtable clash, or when someone asks for age=null as a query.
This will require keeping track of null columns in the index. Something
similar would need to be done for a full delete of the row.
> 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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