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 <jameschurch...@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 <asdk...@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 > >
