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From Philippe <watche...@gmail.com>
Subject Re: Writes slower then reads
Date Thu, 05 Jan 2012 14:19:11 GMT
What if you shutdown the cassandra service on the slow node, does that
improve your read performance ?
If it does then that sole node is responsible for the slow down because it
can't act as a coordinator fast enough.

2012/1/5 R. Verlangen <robin@us2.nl>

> I'm also reading with CL = ONE
>
>
> 2012/1/5 Philippe <watcherfr@gmail.com>
>
>> Depending on the CL you're reading at it will yes : if the CL requires
>> that the "slow" node create a digest of the data and send it to the
>> coordinator then it might explain the poor performance on reads. What is
>> your read CL ?
>>
>> 2012/1/5 R. Verlangen <robin@us2.nl>
>>
>> As I posted this I noticed that the other node's CPU is running high on
>>> some other cronjobs (every couple of minutes to 60% usage). Is the lack of
>>> more CPU cycles a problem in this case?
>>>
>>> Robin
>>>
>>> 2012/1/5 R. Verlangen <robin@us2.nl>
>>>
>>> CPU is idle (< 10% usage). Disk reads occasionally blocks over 32/64K.
>>>> Writes around 0-5MB per second. Network traffic 0.1 / 0.1 MB/s (in / out).
>>>> Paging 0. System int ~ 1300, csw ~ 2500.
>>>>
>>>>
>>>> 2012/1/5 Philippe <watcherfr@gmail.com>
>>>>
>>>>> What can you see in vmstat/dstat ?
>>>>> Le 5 janv. 2012 11:58, "R. Verlangen" <robin@us2.nl> a écrit :
>>>>>
>>>>> Hi there,
>>>>>>
>>>>>> I'm running a cassandra 0.8.6 cluster with 2 nodes (in 2 DC's), RF
=
>>>>>> 2. Actual data on the nodes is only 1GB. Disk latency < 1ms. Disk
>>>>>> throughput ~ 0.4MB/s. OS load always below 1 (on a 8 core machine
with 16GB
>>>>>> ram).
>>>>>>
>>>>>> When I'm running my writes against the cluster with cl = ONE all
>>>>>> reads appear to be faster then the writes.
>>>>>>
>>>>>> Average write speed = 1600us/operation
>>>>>> Average read speed = 200us/operation
>>>>>>
>>>>>> I'm really wondering why this is the case. Anyone got a clue?
>>>>>>
>>>>>> With kind regards,
>>>>>> Robin
>>>>>>
>>>>>
>>>>
>>>
>>
>

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