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From "Benedict (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-6167) Add end-slice termination predicate
Date Fri, 14 Feb 2014 15:08:20 GMT


Benedict commented on CASSANDRA-6167:

This new example doesn't seem to be a good argument for it. If you're attempting outlier detection,
you expect it *not* to be present, and so will ordinarily read the whole 10k events. So it
does not save you anything.

> Add end-slice termination predicate
> -----------------------------------
>                 Key: CASSANDRA-6167
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: API, Core
>            Reporter: Tupshin Harper
>            Priority: Minor
>              Labels: ponies
> When doing performing storage-engine slices, it would sometimes be beneficial to have
the slice terminate for other reasons other than number of columns or min/max cell name.
> Since we are able to look at the contents of each cell as we read it, this is potentially
doable with very little overhead. 
> Probably more challenging than the storage-engine implementation itself, is to come up
with appropriate CQL syntax (Thrift, should we decide to support it, would be trivial).
> Two possibilities ar
> 1) special where function:
> SELECT pk,event from cf WHERE pk IN (1,5,10,11) AND partition_predicate({predicate})
> or a bigger language change, but i think one I prefer. more like:
> 2) SELECT pk,event from cf where pk IN (1,5,10,11) UNTIL PARTITION event {predicate}
> Neither feels perfect, but I do like the fact that the second one at least clearly states
what it is intended to do.
> By using "UNTIL PARTITION", we could re-use the UNTIL keyword to handle other kinds of
early-termination of selects that the coordinator might be able to do, such as stop retrieving
additional rows from shards after a particular criterion was met.

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