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From Aklin_81 <asdk...@gmail.com>
Subject Re: Frequent updates of freshly written columns
Date Fri, 18 Feb 2011 14:11:38 GMT
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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