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Date: Wed, 6 Jun 2012 18:22:41 +0530
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Subject: Re: MeteredFlusher in system.log entries
From: rohit bhatia <rohit2412@gmail.com>
To: user@cassandra.apache.org
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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> w=
rote:
>> See the section on memtable_total_space_in_mb here
>> =A0http://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.jav=
a =3D>
>>
>> "INFO [OptionalTasks:1] 2012-06-05 06:32:05,873 MeteredFlusher.java
>> (line 62) flushing high-traffic column family CFS(Keyspace=3D'Stats',
>> ColumnFamily=3D'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
>>
>>