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From Brian Tarbox <tar...@cabotresearch.com>
Subject Re: How can OpsCenter show me Read Request Latency where there are no read requests??
Date Wed, 16 Jan 2013 18:16:09 GMT
Hmm, that's sense but then why is the latency for the reads that get the
metric often so high (several thousand uSecs) and why does it so closely
track the latency of my normal reads?


On Wed, Jan 16, 2013 at 12:14 PM, Tyler Hobbs <tyler@datastax.com> wrote:

> When you view OpsCenter metrics, you're generating a small number of reads
> to fetch the metric data, which is why your read count is near zero instead
> of actually being zero.  Since reads are still occurring, Cassandra will
> continue to show a read latency.  Basically, you're just viewing the
> latency on the reads to fetch metric data.
>
> Normally the number of reads required to view metrics are small enough
> that they only make a minor difference in your overall read latency
> average, but when you have no other reads occurring, they're the only reads
> that are included in the average.
>
>
> On Tue, Jan 15, 2013 at 9:28 PM, Brian Tarbox <tarbox@cabotresearch.com>wrote:
>
>> I am making heavy use of DataStax OpsCenter to help tune my system and
>> its great.
>>
>> And yet puzzling.  I see my clients do a burst of Reads causing the
>> OpsCenter Read Requests chart to go up and stay up until the clients finish
>> doing their reads.  The read request latency chart also goes up....but it
>> stays up even after all the reads are done.  At last glance I've had next
>> to zero reads for 10 minutes but still have a read request latency thats
>> basically unchanged from when there were actual reads.
>>
>> How am I to interpret this?
>>
>> Thanks.
>>
>> Brian Tarbox
>>
>
>
>
> --
> Tyler Hobbs
> DataStax <http://datastax.com/>
>

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