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 <rohit2412@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 <rohit2412@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 <rohit2412@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 <aaron@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
>>>
>>>