[jira] [Created] (CASSANDRA-6611) Allow for FINAL ttls and FINAL (immutable) inserts to eliminate the need for tombstones

["Donald Smith (JIRA)" <ji...@apache.org>]

Donald Smith created CASSANDRA-6611:
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             Summary: Allow for FINAL ttls and FINAL (immutable) inserts to eliminate the need for tombstones
                 Key: CASSANDRA-6611
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6611
             Project: Cassandra
          Issue Type: New Feature
            Reporter: Donald Smith


Suppose you're not allowed to update the TTL of a column (cell) -- either because CQL is extended to allow syntax like "USING *FINAL* TTL 86400" or because there were a table option saying that TTL is immutable.

If you never update the TTL of a column, then there should be no need for tombstones at all:  any replicas will have the same TTL.  So there’d be no risk of missed deletes.  You wouldn’t even need GCable tombstones.  The purpose of a tombstone is to cover the case where a different node was down and it didn’t notice the delete and it still had the column and tried to replicate it back; but that won’t happen if it too had the TTL.

So, if – and it’s a big if – a table disallowed updates to TTL, then you could really optimize deletion of TTLed columns: you could do away with tombstones entirely.   If a table allows updates to TTL then it’s possible a different node will have the row without the TTL and the tombstone would be needed.

Or am I missing something?

Disallowing updates to rows would seem to enable optimizations in general.   Write-once, non-updatable rows are a common use case. If cassandra had FINAL tables (or FINAL INSERTS) then it could eliminate tombstones for those too. Probably other optimizations would be enabled too.






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