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From Oleg Dulin <>
Subject Re: Commitlog questions
Date Wed, 09 Apr 2014 14:41:59 GMT

To answer your questions:

1) Default is just that, a default. I wouldn't advise raising it 
though. The bigger it is the longer it takes to restart the node.
2) I think they juse use fsync. There is no queue. All files in 
cassandra use java.nio buffers, but they need to be fsynced 
periodically. Look at commitlog_sync parameters in cassandra.yaml file, 
the comments there explain how it works. I believe the difference 
between periodic and batch is just that -- if it is periodic, it will 
fsync every 10 seconds, if it is batch it will fsync if there were any 
changes within a time window.

On 2014-04-09 10:06:52 +0000, Parag Patel said:

>>>>> 1)      Why is the default 4GB?  Has anyone changed this? What
are some 
>>>>> aspects to consider when determining the commitlog size?
>>>>> 2)      If the commitlog is in periodic mode, there is a property
>>>>> set a time interval to flush the incoming mutations to disk.  This 
>>>>> implies that there is a queue inside Cassandra to hold this data in 
>>>>> memory until it is flushed.
>>>>>>>>> a.       Is there a name for this queue?
>>>>>>>>> b.      Is there a limit for this queue?
>>>>>>>>> c.       Are there any tuning parameters for this
> Thanks,
> Parag

Oleg Dulin

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