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From Maxim Potekhin <potek...@bnl.gov>
Subject Re: commit log size
Date Wed, 14 Dec 2011 16:33:49 GMT
Alexandru, Jeremiah --

what setting needs to be tweaked, and what's the recommended value?

I observed similar behavior this morning.

Maxim


On 11/28/2011 2:53 PM, Jeremiah Jordan wrote:
> Yes, the low volume memtables are causing the problem.  Lower the 
> thresholds for those tables if you don't want the commit logs to go 
> crazy.
>
> -Jeremiah
>
> On 11/28/2011 11:11 AM, Alexandru Dan Sicoe wrote:
>> Hello everyone,
>>
>> 4 node Cassandra 0.8.5 cluster with RF=2, replica placement strategy 
>> = SimpleStartegy, write consistency level = ANY, 
>> memtable_flush_after_mins =1440; memtable_operations_in_millions=0.1; 
>> memtable_throughput_in_mb = 40; max_compaction_threshold =32; 
>> min_compaction_threshold =4;
>>
>> I have one keyspace with 1 CF for all the data and 3 other small CFs 
>> for metadata. I am using Datastax OpsCenter to monitor my cluster so 
>> there is another keyspace for monitoring.
>>
>> Everything works ok, the only thing I've noticed is this morning the 
>> commitlog of one node was 52GB, one was 25 GB and the others were 
>> around 3 GB. I left everything untouched and looked a couple of hours 
>> later and the 52GB one is now about 3GB and the 25 GB one is now 29 
>> GB and the other two about the same as before.
>>
>> Are my commit logs growing because of small memtables which don't get 
>> flushed because they don't reach the operations and throughput 
>> limits? Then why do only some nodes exhibit this behaviour?
>>
>> It would be interesting to understand how to control the size of the 
>> commitlog also to know how to size my commitlog disks!
>>
>> Thanks,
>> Alex


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