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From Robert Coli <>
Subject Re: how to store file in the cassandra?
Date Wed, 28 Apr 2010 17:50:40 GMT
On 4/26/10 2:44 AM, dir dir wrote:
> Suppose I have a MPEG video files 15 MB. To save this video file into 
> Cassandra database I will store
> this file into array of byte. One day, I feel this video is not 
> necessary again,
> therefore I delete it from the database. My question is, after I 
> delete this
> video from Cassandra database, should I perform defragmentation operation
> into Cassandra's file database??
Yes, you will need to perform a compaction on the SSTable in order for 
the data to be deleted from disk after a deletion from cassandra cluster.
Thus, a delete operation can't just wipe out all traces of the data 
being removed immediately: if we did, and a replica did not receive the 
delete operation, when it becomes available again it will treat the 
replicas that did receive the delete as having missed a write update, 
and repair them! So, instead of wiping out data on delete, Cassandra 
replaces it with a special value called a tombstone. The tombstone can 
then be propagated to replicas that missed the initial remove request.
Here, we defined a constant, GCGraceSeconds, and had each node track 
tombstone age locally. Once it has aged past the constant, it can be 
GC'd during compaction (see MemtableSStable).


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