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From Kévin LOVATO <>
Subject Re: TTL and gc_grace_period
Date Fri, 05 Jun 2015 16:02:06 GMT
Great, so is there any reason I wouldn't want to set gc_grace_seconds to 0
on an "insert once/ttl only" column family, since it feels like the best
thing to do?

On Fri, Jun 5, 2015 at 5:35 PM, Tyler Hobbs <> wrote:

> On Fri, Jun 5, 2015 at 10:30 AM, Kévin LOVATO <> wrote:
>> I have a column family with data (metrics) that is never overwritten and
>> only deleted using TTLs, and I am wondering if it would be reasonable to
>> have a very low gc_grace_period (even 0) on that CF. I would like to do
>> that mainly to save space and also to prevent tombstone scanning.
> Yes, you can safely lower gc_grace_seconds.  You would only _not_ want to
> lower gc_grace_seconds if you did deletes or overwrote cells with a lower
> TTL.
>> From what I understand of what I could read online, when an expired TTLed
>> column is compacted, it is replaced by a tombstone, so having
>> gc_grace_period would prevent that. Although this would allow the
>> appearance of ghost/zombie columns.
>> The question I'm trying to answer here is the following: Would those
>> ghost columns be able to appear, and if so, would it be a problem, since
>> they would themselves be marked as "expired"?
> You don't need to worry about expired data being revived because every
> node that has a copy of that data will have the same TTL.
> --
> Tyler Hobbs
> DataStax <>

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