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From Karl Hiramoto <>
Subject Re: Compaction doubles disk space
Date Wed, 30 Mar 2011 08:46:34 GMT
On 30/03/2011 09:08, aaron morton wrote:
> Also as far as I understand we cannot immediately delete files because 
> other operations (including repair) may be using them. The data in the 
> pre compacted files is just as correct as the data in the compacted 
> file, it's just more compact. So the easiest thing to do is let the 
> JVM sort out if anything else is using them.
> Perhaps it could be improved by actively tracking which files are in 
> use so they may be deleted quicker. But right so long as unused space 
> is freed when needed it's working as designed AFAIK.

I've run out of space on multiple occasions, and we have nagios alarms 
going off frequently when disk usage is over 90%.   I check cassandra 
and the data/ directory is 2X  to 4X bigger than it needs to be, and no 
compaction or repair is currently running.  I restart the cassandra 
process, or force a GC, it deletes a lot of old SSTables and the data/ 
directory goes down to 1/2 to 1/4  of the size it was a few minutes ago.

Under lots of disk pressure here.


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