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From James Churchman <jameschurch...@gmail.com>
Subject Re: Frequent updates of freshly written columns
Date Fri, 18 Feb 2011 15:24:31 GMT
ok great, thanks for the exact clarification

On 18 Feb 2011, at 14:11, Aklin_81 wrote:

> Compaction does not 'mutate' the sst files, it 'merges' several sst files into one with
new indexes, merged data rows & deleting tombstones. Thus you reclaim your disk space.
> 
> 
> On Fri, Feb 18, 2011 at 7:34 PM, James Churchman <jameschurchman@gmail.com> wrote:
> 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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