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 <wz1...@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 <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 > > > > > > > > >