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From Brian Tarbox <tar...@cabotresearch.com>
Subject Re: Is this how to read the output of nodetool cfhistograms?
Date Tue, 22 Jan 2013 15:27:15 GMT
Indeed, but how many Cassandra users have the good fortune to stumble
across that page?  Just saying that the explanation of the very powerful
nodetool commands should be more front and center.

Brian


On Tue, Jan 22, 2013 at 10:03 AM, Edward Capriolo <edlinuxguru@gmail.com>wrote:

> This was described in good detail here:
>
> http://thelastpickle.com/2011/04/28/Forces-of-Write-and-Read/
>
> On Tue, Jan 22, 2013 at 9:41 AM, Brian Tarbox <tarbox@cabotresearch.com>wrote:
>
>> Thank you!   Since this is a very non-standard way to display data it
>> might be worth a better explanation in the various online documentation
>> sets.
>>
>> Thank you again.
>>
>> Brian
>>
>>
>> On Tue, Jan 22, 2013 at 9:19 AM, Mina Naguib <mina.naguib@adgear.com>wrote:
>>
>>>
>>>
>>> On 2013-01-22, at 8:59 AM, Brian Tarbox <tarbox@cabotresearch.com>
>>> wrote:
>>>
>>> > The output of this command seems to make no sense unless I think of it
>>> as 5 completely separate histograms that just happen to be displayed
>>> together.
>>> >
>>> > Using this example output should I read it as: my reads all took
>>> either 1 or 2 sstable.  And separately, I had write latencies of 3,7,19.
>>>  And separately I had read latencies of 2, 8,69, etc?
>>> >
>>> > In other words...each row isn't really a row...i.e. on those 16033
>>> reads from a single SSTable I didn't have 0 write latency, 0 read latency,
>>> 0 row size and 0 column count.  Is that right?
>>>
>>> Correct.  A number in any of the metric columns is a count value
>>> bucketed in the offset on that row.  There are no relationships between
>>> other columns on the same row.
>>>
>>> So your first row says "16033 reads were satisfied by 1 sstable".  The
>>> other metrics (for example, latency of these reads) is reflected in the
>>> histogram under "Read Latency", under various other bucketed offsets.
>>>
>>> >
>>> > Offset      SSTables     Write Latency      Read Latency          Row
>>> Size      Column Count
>>> > 1              16033             0                            0
>>>                      0                 0
>>> > 2                303               0                            0
>>>                        0                 1
>>> > 3                  0                 0                            0
>>>                          0                 0
>>> > 4                  0                 0                            0
>>>                          0                 0
>>> > 5                  0                 0                            0
>>>                          0                 0
>>> > 6                  0                 0                            0
>>>                          0                 0
>>> > 7                  0                 0                            0
>>>                          0                 0
>>> > 8                  0                 0                            2
>>>                          0                 0
>>> > 10                 0                 0                            0
>>>                          0              6261
>>> > 12                 0                 0                            2
>>>                          0               117
>>> > 14                 0                 0                            8
>>>                          0                 0
>>> > 17                 0                 3                           69
>>>                          0               255
>>> > 20                 0                 7                          163
>>>                          0                 0
>>> > 24                 0                19                         1369
>>>                          0                 0
>>> >
>>>
>>>
>>
>

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