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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