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From "Sylvain Lebresne (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-5149) Respect slice count even if column expire mid-request
Date Tue, 26 Feb 2013 10:50:12 GMT


Sylvain Lebresne commented on CASSANDRA-5149:

bq. I have trouble coming up with a use case for it.

You mean, for querying the expiration time of a column? My own experience with TTL leads me
to believe that anyone using expiring columns will want to query the expiration time at one
point or another. I personally had a case where if some TTLed columns were read, we were "extending"
the TTL and how long it was extended depended on the current expiration time. Or, on the other
end of the spectrum, wanting to update a column value without extending the TTL. I had also
a number of case where not all columns had the same TTL, if any, and just knowing if the column
was an expiring one was necessary (including but not limited to checking during development
that the code was doing what it was supposed to do in terms of setting TTLs).

Also, if we were to transform expiring column to standard column on read, even ignoring the
fact that we wouldn't be able to return the expiration time to clients, you'd have to be careful
about read-repair "cancelling" your TTLs.  

Besides, as said above, especially if it's fix-for 2.0 (and so things like "this may require
a protocol change" become largely irrelevant), I think normalizing all code on having expiration
be based on a time fixed at well know places (like we do for gcBefore really) is the right
long term solution.
> Respect slice count even if column expire mid-request
> -----------------------------------------------------
>                 Key: CASSANDRA-5149
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>    Affects Versions: 0.7.0
>            Reporter: Sylvain Lebresne
>             Fix For: 2.0
> This is a follow-up of CASSANDRA-5099.
> If a column expire just while a slice query is performed, it is possible for replicas
to count said column as live but to have the coordinator seeing it as dead when building the
final result. The effect that the query might return strictly less columns that the requested
slice count even though there is some live columns matching the slice predicate but not returned
in the result.

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