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 > > >
