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 <tar...@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 <edlinuxg...@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 <tar...@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.nag...@adgear.com> wrote: >> >> >>> >>>On 2013-01-22, at 8:59 AM, Brian Tarbox <tar...@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 >>>> >>> >>> >> >
