incubator-cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From horschi <hors...@gmail.com>
Subject Re: TTL, Tombstones, and gc_grace
Date Thu, 25 Jul 2013 13:42:41 GMT
Hi Michael,

yes, you should never loose a delete, because there are no real deletes. No
matter what version you are using.

btw: There is actually a ticket that builds an optimization on top of that
assumption: CASSANDRA-4917. Basically, if TTL>gc_grace then do not create
tombstones for expiring-columns. This works because disappear anyway if TTL
is over.

cheers,
Christian


On Thu, Jul 25, 2013 at 3:24 PM, Michael Theroux <mtheroux2@yahoo.com>wrote:

> Hello,
>
> Quick question on Cassandra, TTLs, tombstones, and GC grace.  If we have a
> column family whose only mechanism of deleting columns is utilizing TTLs,
> is repair really necessary to make tombstones consistent, and therefore
> would it be safe to set the gc grace period of the column family to a very
> low value?
>
> I ask because of this blog post based on Cassandra .7:
> http://www.datastax.com/dev/blog/whats-new-cassandra-07-expiring-columns.
>
> "The first time the expired column is compacted, it is transformed into a
> tombstone. This transformation frees some disk space: the size of the value
> of the expired column. From that moment on, the column is a normal
> tombstone and follows the tombstone rules: it will be totally removed by
> compaction (including minor ones in most cases since Cassandra 0.6.6) after
> GCGraceSeconds."
>
> Since tombstones are not written using a replicated write, but instead
> written during compaction, theoretically, it shouldn't be possible to lose
> a tombstone?  Or is this blog post inaccurate for later versions of
> cassandra?  We are using cassandra 1.1.11.
>
> Thanks,
> -Mike
>
>
>

Mime
View raw message