I am not sure, but I think there should be only 6 memtables (max) based on the example. 1 is active, 4 are in the queue, 1 is being flushed.
Is this correct? On Wed, Jun 6, 2012 at 9:08 PM, rohit bhatia <rohit2...@gmail.com> wrote: > Also, Could someone please explain how the factor of 7 comes in the > picture in this sentence > > "For example if memtable_total_space_in_mb is 100MB, and > memtable_flush_writers is the default 1 (with one data directory), and > memtable_flush_queue_size is the default 4, and a Column Family has no > secondary indexes. The CF will not be allowed to get above one seventh > of 100MB or 14MB, as if the CF filled the flush pipeline with 7 > memtables of this size it would take 98MB. " > > On Wed, Jun 6, 2012 at 6:22 PM, rohit bhatia <rohit2...@gmail.com> wrote: > > Hi.. > > > > the link http://thelastpickle.com/2011/05/04/How-are-Memtables-measured/ > > mentions that "From version 0.7 onwards the worse case scenario is up > > to CF Count + Secondary Index Count + memtable_flush_queue_size > > (defaults to 4) + memtable_flush_writers (defaults to 1 per data > > directory) memtables in memory the JVM at once.". > > > > So it implies that for flushing, Cassandra copies the memtables content. > > So does this imply that writes to column families are not stopped even > > when it is being flushed? > > > > Thanks > > Rohit > > > > On Wed, Jun 6, 2012 at 9:42 AM, rohit bhatia <rohit2...@gmail.com> > wrote: > >> Hi Aaron > >> > >> Thanks for the link, I have gone through it. But this doesn't justify > >> nodes of exactly same config/specs differing in their flushing > >> frequency. > >> The traffic on all node is same as we are using RandomPartitioner > >> > >> Thanks > >> Rohit > >> > >> On Wed, Jun 6, 2012 at 12:24 AM, aaron morton <aa...@thelastpickle.com> > wrote: > >>> See the section on memtable_total_space_in_mb here > >>> http://thelastpickle.com/2011/05/04/How-are-Memtables-measured/ > >>> > >>> Cheers > >>> ----------------- > >>> Aaron Morton > >>> Freelance Developer > >>> @aaronmorton > >>> http://www.thelastpickle.com > >>> > >>> On 6/06/2012, at 2:27 AM, rohit bhatia wrote: > >>> > >>> I am trying to understand the variance in flushes frequency in a 8 > >>> node Cassandra cluster. > >>> All the flushes are of the same type and initiated by > MeteredFlusher.java => > >>> > >>> "INFO [OptionalTasks:1] 2012-06-05 06:32:05,873 MeteredFlusher.java > >>> (line 62) flushing high-traffic column family CFS(Keyspace='Stats', > >>> ColumnFamily='Minutewise_Channel_Stats') (estimated 501695882 bytes)" > >>> [taken from system.log] > >>> > >>> Number of flushes for 1 column family vary from 6 flushes per day to > >>> 24 flushes per day among nodes of same configuration and same > >>> hardware. > >>> Could you please throw light on the what conditions does > >>> MeteredFlusher use to trigger memtable flushes. > >>> Also how accurate is the estimated size in the above logfile entry. > >>> > >>> Regards > >>> Rohit Bhatia > >>> Software Engineer, Media.net > >>> > >>> >
