Thanks samal... I got it now.... On Thu, Jul 21, 2011 at 4:11 PM, samal <sa...@wakya.in> wrote:
> > Any ways , some where memtable has to be stored right, like we say memtable > data is flushed to create sstable on disk. > >> Exactly from which location or memory it will be getting from. is it like >> an objects streams or like it is storing the values in commitlog. >> > > A Memtable is Cassandra's in-memory representation of key/value pairs. > > >> my next question is , data is written to commit log. all the data is >> available here, and the sstable are getting created on disk, then where and >> when these memtables are coming into picture > > > Commitlog is append only file which record write sequentially, more[2], can > be thought as check sum file, which to used to recalculate data for > memtables in case of crash. > A write first hits the *CommitLog*, then Cassandra stores/writes values to > in-memory data structures called Memtables. The Memtables are flushed to > disk whenever one of the configurable thresholds is met.[3] > <http://wiki.apache.org/cassandra/MemtableThresholds> > For each column family there is corresponding memtable. > There is generally one commitlog file for all CF. > > SSTables are immutable once written to disk cannot be modified. It will > only be replaced by new SSTable after compaction > > > [1]http://wiki.apache.org/cassandra/ArchitectureOverview > [2]http://wiki.apache.org/cassandra/ArchitectureCommitLog > [3]http://wiki.apache.org/cassandra/MemtableThresholds > >
