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From Andy Burgess <>
Subject Time-to-live on SuperColumns
Date Wed, 19 Jan 2011 11:36:44 GMT

I'm trying to use the time-to-live functionality, which I've patched 
into Cassandra 0.6.6. My problem is that my sstables are not emptying. 
When my data expires, they do reduce in size, but only by a fraction of 
what I expected. I've come to realise that this must be because I've set 
the TTL on my Columns, but actually, I need the SuperColumns to expire 
too - I believe that my sstables remain large because I (probably) have 
a lot of empty SuperColumns. Unfortunately, I can't see a way to set a 
TTL on a SuperColumn.

Does anyone have any suggestions for what I can do here?

Actually, I've also just been playing with a few tests of "manually" 
deleting a SuperColumn, rather than using TTL - i.e. using Hector's 
Deletion with setSuper_column. Whilst this appears to work as far as 
making the data unavailable to the client is concerned, it only appears 
to reduce sstable size by about three quarters. This is in the case 
where I know that the sstable contains only my test inserts, which I 
have completely deleted. Why doesn't the sstable reduce in size to 
(almost) nothing?


Andy Burgess
Principal Development Engineer
Application Delivery
WorldPay Ltd.
270-289 Science Park, Milton Road
Cambridge, CB4 0WE, United Kingdom (Depot Code: 024)
Office: +44 (0)1223 706 779| Mobile: +44 (0)7909 534 940

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