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From Mike <>
Subject Column Family migration/tombstones
Date Sat, 29 Dec 2012 19:51:43 GMT

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.


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