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From aaron morton <aa...@thelastpickle.com>
Subject Re: Column Family migration/tombstones
Date Wed, 02 Jan 2013 23:41:15 GMT
> 1) As one can imagine, the index and bloom filter for this column family is large.  Am
I correct to assume that bloom filter and index space will not be reduced until after gc_grace_period?
Yes. 

> 2) If I would manually run repair across a cluster, is there a process I can use to safely
remove these tombstones before gc_grace period to free this memory sooner?
There is nothing to specifically purge tombstones. 

You can temporarily reduce the gc_grace_seconds and then trigger compaction. Either by reducing
the min_compaction_threshold to 2 and doing a flush. Or by kicking of a user defined compaction
using the JMX interface. 

> 3) Any words of warning when undergoing this?
Make sure you have a good breakfast. 
(It's more general advice than Cassandra specific.)


Cheers

-----------------
Aaron Morton
Freelance Cassandra Developer
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 30/12/2012, at 8:51 AM, Mike <mtheroux2@yahoo.com> wrote:

> Hello,
> 
> We are undergoing a change to our internal datamodel that will result in the eventual
deletion of over a hundred million rows from a Cassandra column family.  From what I understand,
this will result in the generation of tombstones, which will be cleaned up during compaction,
after gc_grace_period time (default: 10 days).
> 
> A couple of questions:
> 
> 1) As one can imagine, the index and bloom filter for this column family is large.  Am
I correct to assume that bloom filter and index space will not be reduced until after gc_grace_period?
> 
> 2) If I would manually run repair across a cluster, is there a process I can use to safely
remove these tombstones before gc_grace period to free this memory sooner?
> 
> 3) Any words of warning when undergoing this?
> 
> We are running Cassandra 1.1.2 on a 6 node cluster and a Replication Factor of 3.  We
use LOCAL_QUORM consistency for all operations.
> 
> Thanks!
> -Mike


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