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From Sankalp Kohli <kohlisank...@gmail.com>
Subject Re: Recommended amount of free disk space for compaction
Date Fri, 29 Nov 2013 11:48:19 GMT
Apart from the compaction, you might want to also look at free space required for repairs.
This could be problem if you have large rows as repair is not at column level. 




> On Nov 28, 2013, at 19:21, Robert Wille <rwille@fold3.com> wrote:
> 
> I’m trying to estimate our disk space requirements and I’m wondering about disk space
required for compaction.
> 
> My application mostly inserts new data and performs updates to existing data very infrequently,
so there will be very few bytes removed by compaction. It seems that if a major compaction
occurs, that performing the compaction will require as much disk space as is currently consumed
by the table. 
> 
> So here’s my question. If Cassandra only compacts one table at a time, then I should
be safe if I keep as much free space as there is data in the largest table. If Cassandra can
compact multiple tables simultaneously, then it seems that I need as much free space as all
the tables put together, which means no more than 50% utilization. So, how much free space
do I need? Any rules of thumb anyone can offer?
> 
> Also, what happens if a node gets low on disk space and there isn’t enough available
for compaction? If I add new nodes to reduce the amount of data on each node, I assume the
space won’t be reclaimed until a compaction event occurs. Is there a way to salvage a node
that gets into a state where it cannot compact its tables?
> 
> Thanks
> 
> Robert
> 

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