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
>
