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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Cassandra and TTL
Date Tue, 12 Jan 2010 16:56:09 GMT
I'm skeptical that this is a common use-case...  If truncating old
sstables entirely
(https://issues.apache.org/jira/browse/CASSANDRA-531) meets your
needs, that is going to be less work and more performant.

-Jonathan

On Tue, Jan 12, 2010 at 10:45 AM, Sylvain Lebresne <sylvain@yakaz.com> wrote:
> Hello,
>
> I have to deal with a lot of different data and Cassandra seems to be a good
> fit for my needs so far. However, some of this data is volatile by nature and
> for those, I would need to set something akin to a TTL. Those TTL could be
> long, but keeping those data forever would be useless.
>
> I could deal with that by hand, writing some daemon that run regularly and
> remove what should be removed. However this is not particularly efficient, nor
> convenient, and I would find it really cool to be able to provide a TTL when
> inserting something and don't have to care more than that.
>
> Which leads me to my question: why Cassandra doesn't allow to set a TTL for
> data ? Is it for technical reason ? For philosophical reason ? Or just nobody
> had needed it sufficiently to write it ?
>
> From what I understand of how Cassandra works, it seems to me that it
> could be done pretty efficiently (even though I agree that it wouldn't
> be a minor
> change). That is, it would require to add a ttl to column (and/or row). When
> reading a column whose timestamp + ttl is expired, it would ignore it (as for
> tombstoned column). Then during compaction, expired column would be
> collected.
>
> Is there any major difficulties/obstacles I don't see ?
> Or maybe is there some trick I don't know about that allow to do such a thing
> already ?
>
> And if not, would that be something that would interest the Cassandra
> community ? Or does nobody ever need such a thing ? (I personally believe it
> to be a desirable feature, but maybe I am the only one.)
>
> Thanks,
> Sylvain
>

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