I have two CFs in my keyspace.  one i care about allowing a good amount of time 
for tombstones to propagate (GCGraceSeconds large) ... but the other i couldn't 
care and in fact i want them gone ASAP so i don't iterate over them.  has any 
thought been given to making this setting per Keyspace or per ColumnFamily?

my scenario is that i add columns to rows in one CF, UserData, with logging 
data or activity, but we only want to keep, say 5000 columns per user.  So i 
also store the user's ID in another CF, PruneCollection, and periodically 
iterate over it using the IDs found in PruneCollection to "prune" the columns 
in UserData - and then immediately delete the ID from PruneCollection.  if the 
code is adding, say 50 IDs per second to PruneCollection then the number of 
deleted keys starts to build up, forcing my iterator to skip over large amounts 
of deleted keys.  With a small GCGraceSeconds these keys are removed nicely, 
but i can't do that because it affects the tombstones in UserData as well, 
which need to be propagated.

thoughts?

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