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From Brian Tarbox <tar...@cabotresearch.com>
Subject Re: Is this how to read the output of nodetool cfhistograms?
Date Wed, 23 Jan 2013 16:02:36 GMT
Wei,
Thank you for the explanation (Offset is always the x-axis, the other
columns represent the y-axis (taken 5 independent times)).

Part of this still doesn't make sense.  If I look at just read latencies
for example...am I to believe that 1916 times I had a latency of exactly
3229500 usecs?  Is this just some weird 5-independent variable mushed
together data bucketing???

        Offset                SSTables         Write Lat     Read Lat
   1109 0 349 642406  1331 0 147 1335840  1597 0 121 640374  *1916* 0 117 *
3229500*  2299 0 91 683749  2759 0 77 202722


On Tue, Jan 22, 2013 at 12:11 PM, Wei Zhu <wz1975@yahoo.com> wrote:

> I agree that Cassandra cfhistograms is probably the most bizarre metrics I
> have ever come across although it's extremely useful.
>
> I believe the offset is actually the metrics it has tracked (x-axis on the
> traditional histogram) and the number under each column is how many times
> that value has been recorded (y-axis on the traditional histogram). Your
> write latency are 17, 20, 24 (microseconds?). 3 writes took 17, 7 writes
> took 20 and 19 writes took 24
>
> Correct me if I am wrong.
>
> Thanks.
> -Wei
>
>   ------------------------------
> *From:* Brian Tarbox <tarbox@cabotresearch.com>
> *To:* user@cassandra.apache.org
> *Sent:* Tuesday, January 22, 2013 7:27 AM
> *Subject:* Re: Is this how to read the output of nodetool cfhistograms?
>
> 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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