Couple of hits here, one from jonathan and some previous discussions on the user list http://www.google.co.nz/search?q=cassandra+iostat
Same here for cfhistograms http://www.google.co.nz/search?q=cassandra+cfhistograms
cfhistograms includes information on the number of sstables read during recent requests. As
your initial cfstats showed 236 sstables I thought it may be useful see if there was a high
number of sstables been accessed per read.
70 requests per second is slow against a 6 node cluster where each node has 12 cores and 96GB
of ram. Something is not right.
Aaron
On 12 Apr 2011, at 17:11, mcasandra wrote:
>
> aaron morton wrote:
>>
>> You'll need to provide more information, from the TP stats the read stage
>> could not keep up. If the node is not CPU bound then it is probably IO
>> bound.
>>
>>
>> What sort of read?
>> How many columns was it asking for ?
>> How many columns do the rows have ?
>> Was the test asking for different rows ?
>> How many ops requests per second did it get up to?
>> What do the io stats look like ?
>> What does nodetool cfhistograms say ?
>>
> It's simple read of 1M rows with one column of avg size of 200K. Got around
> 70 req per sec.
>
> Not sure how to intepret the iostats output with things happening async in
> cassandra. Can you give little description on how to interpret it?
>
> I have posted output of cfstats. Does cfhistograms provide better info?
>
>
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