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From Sylvain Lebresne <sylv...@datastax.com>
Subject Re: Using ttl to expire columns rather than using delete
Date Wed, 12 Oct 2011 15:32:53 GMT
On Wed, Oct 12, 2011 at 3:51 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
> Well, the reason you'd want to run repair is to get the tombstone on
> nodes that missed the insert.  And that would only be important if you
> sometimes generate inserts that would be otherwise shadowed by the
> tombstone, right?

The initial question was about "can I use inserting with ttl=1 instead of
issuing deletes", so that would be a case where you do shadow a previous
version with a very small ttl and so repair is important.

But you're right that if you only issue data with expiration (no deletes) and
that you
  * either do not overwrite columns
  * or are sure that when you do overwrite, the value you're overwriting has
     a ttl that is lesser or equal than the ttl of the value you're
overwriting with
     (+gc_grace to be precise)
then yes, repair is not necessary because you can't have shadowed value
resurfacing. And that's the case Eric is talking about btw.

But again, using inserts with tiny ttl in place of tombstones is not
one of those situation, so repair is necessary as usual.

--
Sylvain


>
> On Wed, Oct 12, 2011 at 2:17 AM, Sylvain Lebresne <sylvain@datastax.com> wrote:
>> Unfortunately, expiring column are no magic bullet. If you insert
>> columns with ttl=1,
>> you're roughly doing the same thing than deleting, so the exact same
>> rule concerning
>> repair applies.
>>
>> What can be said on repair and expiring columns (and that may or may
>> not be helpful)
>> is that if you have a column family on which all and every column you
>> insert has a
>> ttl > n (for some n, including n = infinity) and ttl are your only
>> means of deletion for
>> that CF (i.e, no deletes), then it would be enough to run repair on
>> that column family
>> only every gc_grace + n period of time (instead of every gc_grace period).
>>
>> --
>> Sylvain
>>
>> On Wed, Oct 12, 2011 at 3:49 AM, Terry Cumaranatunge <cumarana@gmail.com> wrote:
>>> Hello,
>>>
>>> If you set a ttl and expire a column, I've read that this eventually turns
>>> into a tombstone and will be cleaned out by the GC. Are expirations
>>> considered a form of delete that still requires a node repair to be run in
>>> gc_grace_period seconds? The operations guide says you have to run node
>>> repair if you have deletes, so I'm trying to find out if we can upsert the
>>> column with expirations using a ttl=1 to substitute deletes. The node repair
>>> operations is very intensive in our environment and causes a
>>> significant performance degradation on the system.
>>>
>>> Thanks
>>
>
>
>
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of DataStax, the source for professional Cassandra support
> http://www.datastax.com
>

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