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https://issues.apache.org/jira/browse/CASSANDRA-9779?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14623464#comment-14623464
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Jonathan Ellis commented on CASSANDRA-9779:
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Since {{INSERT}} and {{UPDATE}} are semantically identical I don't think it's
worth disallowing UPDATE on these tables. Instead, we would define our
behavior to be: if you violate the INSERTS ONLY contract by updating existing
rows, Cassandra will give you one of those versions back when you query it, but
not necessarily the most recent. This allows us to preserve our optimizations
while doing something reasonable in the face of a broken contract.
> Append-only optimization
> ------------------------
>
> Key: CASSANDRA-9779
> URL: https://issues.apache.org/jira/browse/CASSANDRA-9779
> Project: Cassandra
> Issue Type: New Feature
> Components: API, Core
> Reporter: Jonathan Ellis
> Fix For: 3.x
>
>
> Many common workloads are append-only: that is, they insert new rows but do
> not update existing ones. However, Cassandra has no way to infer this and so
> it must treat all tables as if they may experience updates in the future.
> If we added syntax to tell Cassandra about this ({{WITH INSERTS ONLY}} for
> instance) then we could do a number of optimizations:
> - Compaction would only need to worry about defragmenting partitions, not
> rows. We could default to DTCS or similar.
> - CollationController could stop scanning sstables as soon as it finds a
> matching row
> - Most importantly, materialized views wouldn't need to worry about deleting
> prior values, which would eliminate the majority of the MV overhead
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