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From Ramesh Natarajan <rames...@gmail.com>
Subject Re: help needed interpreting Read/Write latency in cfstats and cfhistograms output
Date Mon, 03 Oct 2011 20:57:06 GMT
Thanks Aaron. The ms in the latency is it microseconds or milliseconds?

I ran the 2 commands at the same time. I was expecting the values to be in
the some what similar but from my output earlier ,  you can see the median
in read latency in histogram output is about 10 milliseconds whereas the
cfstats showed 5 ms.  Is this normal?

thanks
Ramesh


On Mon, Oct 3, 2011 at 3:40 PM, aaron morton <aaron@thelastpickle.com>wrote:

> Hi Rameash,
>
>        Both tools output the "recent" latency, and while they do this
> slightly differently, the result is that it's the latency since the last
> time it was checked. Also the two tools use different counters, so using
> cfstats will not update cfhistogram.
>
>
>        So when you see
> >  Read Latency: 5.086 ms.
> >  Write Latency: 0.018 ms.
> It means since you last checked the average latency for requests was 5.086
> and 0.018ms
>
> When you see
> > Offset      SSTables     Write Latency      Read Latency          Row
> Size      Column Count
> > 1            4148086                 9            198896
> 0                 0
>
> it means that 198,896 read requests were completed in 1 *microsecond* and 9
> write requests completed n 1 microsecond.
>
> Cheers
>
>
> -----------------
> Aaron Morton
> Freelance Cassandra Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 4/10/2011, at 4:58 AM, Ramesh Natarajan wrote:
>
> > I am running a cassandra 0.8.6 cluster. I started a clean test setup and
> run my tests for a while. Later when I run cfstats and cfhistograms ( both
> ran at the same time )
> > the values for Read/Write latency doesn't match.   As per  cfstats  the
> latency for read and write are 5.086 and 0.018 ms respectively. However per
> cfhistogram output the
> > latency doesn't look correct. Attached are the output.. Can someone
> explain how to correlate the data?
> >
> > Thanks
> > Ramesh
> >
> >
> > cfstats
> > Column Family: uid
> >                 SSTable count: 10
> >                 Space used (live): 7453864915
> >                 Space used (total): 7453864915
> >                 Number of Keys (estimate): 2669184
> >                 Memtable Columns Count: 6864
> >                 Memtable Data Size: 9254197
> >                 Memtable Switch Count: 1037
> >                 Read Count: 353627031
> >                 Read Latency: 5.086 ms.
> >                 Write Count: 325803780
> >                 Write Latency: 0.018 ms.
> >                 Pending Tasks: 0
> >                 Key cache capacity: 2000000
> >                 Key cache size: 2000000
> >                 Key cache hit rate: 0.8106968059650433
> >                 Row cache: disabled
> >                 Compacted row minimum size: 104
> >                 Compacted row maximum size: 11864
> >                 Compacted row mean size: 2629
> >
> >
> > cfhistograms for uid
> > MSA/uid histograms
> > Offset      SSTables     Write Latency      Read Latency          Row
> Size      Column Count
> > 1            4148086                 9            198896
> 0                 0
> > 2            8680130                 2            993805
> 0                 0
> > 3           17138720                 2           2487034
> 0                 0
> > 4           29039539                 3           4712246
> 0                 0
> > 5           41925392                20           7805708
> 0                 0
> > 6           52669945               126          11641747
> 0                 0
> > 7           57474130               457          15812298
> 0                 0
> > 8           53613212              1034          19846340
> 0                 0
> > 10          67641689              5463          48797478
> 0                 0
> > 12          19456795             15703          52875124
> 0                 0
> > 14           1841556             35196          47573455
> 0                 0
> > 17              3095            102787          51065577
> 0                 0
> > 20                 0            145706          27439942
> 0                 0
> > 24                 0            196614          14573201
> 0                 0
> > 29                 0            237579           4983641
> 0                 0
> > 35                 0            489150           2167481
> 0                 0
> > 42                 0           1234257           2613908
> 0                 0
> > 50                 0           2623421           2887838
> 0                 0
> > 60                 0           5991578           1767507
> 0                 0
> > 72                 0          13091537           1187687
> 0                 0
> > 86                 0          23362939           1001303
> 0                 0
> > 103                0          34216661            966773
> 0                 0
> > 124                0          39232688            580505
>  3790              3790
> > 149                0          33531717            411380
> 63631             63631
> > 179                0          28741050            297513
> 11083             11083
> > 215                0          26604624            211311
> 82446             82446
> > 258                0          23621426            152905
> 16650             16650
> > 310                0          21389177            115147
> 77831             77831
> > 372                0          17854763             89825
> 77962             77962
> > 446                0          12658366             73162
> 63647             63647
> > 535                0           8777140             62366
> 55015             55015
> > 642                0           6714295             58156
> 89230             89230
> > 770                0           5919024             52929
> 50298             50298
> > 924                0           5793271             49989
> 45053             45053
> > 1109               0           5793698             45865
> 41470             41470
> > 1331               0           5451214             42312
> 87700             87700
> > 1597                           4720406             32027
>  220189            220189
> > 1916                           3745143             27804
>  313070            313070
> > 2299                           2864750             27902
>  188374            188374
> > 2759                           2123842             19042
> 51096             51096
> > 3311                           1560835             17596
>  4718              4718
> > 3973                           1188835             11658
>  4045              4045
> > 4768                            976833              9965
> 33284             33284
> > 5722                            911089              7722
>  192321            192321
> > 6866                            923357              5895
>  428685            428685
> > 8239                            957669              4667
>  217879            217879
> > 9887                            866131              3357
>  9478              9478
> > 11864                           708365              2506
>  11                11
> > 14237                           630587              1847
> 0                 0
> > 17084                           557397              1397
> 0                 0
> > 20501                           499436              1049
> 0                 0
> > 24601                           457665               779
> 0                 0
> > 29521                           435142               597
> 0                 0
> > 35425                           415220               470
> 0                 0
> > 42510                           393854               375
> 0                 0
> > 51012                           372677               206
> 0                 0
> > 61214                           352421               152
> 0                 0
> > 73457                           326874               107
> 0                 0
> > 88148                           304298                85
> 0                 0
> > 105778                          285494               115
> 0                 0
> > 126934                          275249               163
> 0                 0
> > 152321                          258549               125
> 0                 0
> > 182785                          242338                89
> 0                 0
> > 219342                          235146                48
> 0                 0
> > 263210                          242166                28
> 0                 0
> > 315852                          241692                22
> 0                 0
> > 379022                          175100                10
> 0                 0
> > 454826                          131247                 6
> 0                 0
> > 545791                          161308                 9
> 0                 0
> > 654949                          317944                 4
> 0                 0
> > 785939                          554445                 1
> 0                 0
> > 943127                          230545                 0
> 0                 0
> > 1131752                          63083                 0
> 0                 0
> > 1358102                          36235                 0
> 0                 0
> > 1629722                          41269                 0
> 0                 0
> > 1955666                          10652                 0
> 0                 0
> > 2346799                           3113                 0
> 0                 0
> > 2816159                           1016                 1
> 0                 0
> > 3379391                            148                 0
> 0                 0
> > 4055269                             18                 0
> 0                 0
> > 4866323                              9                 0
> 0                 0
> > 5839588                              0                 0
> 0                 0
> > 7007506                              0                 0
> 0                 0
> > 8409007                              0                 0
> 0                 0
> > 10090808                             0                 0
> 0                 0
> > 12108970                             0                 0
> 0                 0
> > 14530764                             0                 0
> 0                 0
> > 17436917                             0                 0
> 0                 0
> > 20924300                             0                 0
> 0                 0
> > 25109160                             0                 0
> 0                 0
> >
>
>

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