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From James Churchman <jameschurch...@gmail.com>
Subject Re: Frequent updates of freshly written columns
Date Fri, 18 Feb 2011 14:04:46 GMT
but a compaction will mutate the sstables and reclaim the space (eventually)  ? 


james

On 18 Feb 2011, at 08:36, Sylvain Lebresne wrote:

> On Fri, Feb 18, 2011 at 8:14 AM, Aklin_81 <asdkl93@gmail.com> wrote:
> Are the very freshly written columns to a row in memtables, efficiently updated/overwritten
by edited/new column values. 
> 
> After flushing of memtable, are those(edited + unedited ones) columns stored together
on disk (in same blocks!?) as if they were written in one single operation or same time ??
I know if old columns are edited then several copies of same column will be dispersed in different
sst tables, what about fresh columns ?
> 
> Are there any disadvantages to frequently updating fresh columns present in memtable
? 
> 
> The SSTables are immutable but the memtable are not. As long as you update/overwrite
a column that is still in memtable, it is simply replaced in memory (so it's as efficient
as it gets).
> In other words, when the memtable is flushed, only the last version of the column goes
in. 
> 
> --
> Sylvain


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