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From Stefan Reek <ste...@unitedgames.com>
Subject Re: Impact of old data on performance
Date Thu, 01 Mar 2012 10:13:41 GMT
Swap is disabled on the machines, so I'm sure the JVM is not swapping out.
Cassandra is the only process running on those machines, so network 
contention shouldn't be an issues either.
Which leaves Garbage collection.

In the logs I can see that the Garbage Collection takes a long time, for 
example:

GCInspector.java (line 130) GC for ConcurrentMarkSweep: 384113 ms, 
-84703136 reclaimed leaving 1018203472 used; max is 17208836096

But I configured the Garbage Collector to use the ConcurrentMarkSweep 
algorithm. As far as I understand this means that there will only be two 
pauses during the compaction, the mark and the remark stage.

As I also have extra garbage collection logging enabled on one node, I 
checked to see if the mark/remark times sometimes exceed the 10 second 
RPC timeout and I found some logging statements like this:

422208.422: [CMS-concurrent-mark: 0.434/20.004 secs] [Times: user=13.40 
sys=0.75, real=20.00 secs]

Does this mean that the mark session took over 10 seconds and all other 
Cassandra threads were stopped during this
time? If so, that would explain why I sometimes get timeouts on requests 
and also see Dropped Messages in my logs.

Cheers,

Stefan


On 02/29/2012 07:48 PM, Dan Retzlaff wrote:
> First to be clear, I'm not an expert but I suggested "cfstats" because 
> it can show unhealthy signs. That said, yours looks okay to me: few 
> live SSTables per column family, reasonable quantity of data... The 
> next things I'd verify are that (1) the JVM isn't swapping out during 
> these periods of bad performance, (2) GC completes in less than your 
> RPC timeout (check the logs), and (3) your internode network 
> connection isn't degraded by another application.
>
> The fact that *writes* are timing out is interesting, since existing 
> data should have little to no effect on those.
>
> BTW, since ColumnFamily7 sees most of your action, you might consider 
> whether a key/row cache is appropriate. By my count it has 2M rows and 
> 7M reads since startup. But this fine-tuning is probably a distraction 
> from whatever's causing your timeouts.
>
> Hope that helps,
> Dan
>
> On Wed, Feb 29, 2012 at 5:14 AM, Stefan Reek <stefan@unitedgames.com 
> <mailto:stefan@unitedgames.com>> wrote:
>
>     Hi Dan,
>
>     Thanks for answering.
>     I included the output of cfstats below.
>     I hope you can say something about our problems with it.
>
>     cheers,
>
>     Stefan
>
>     Keyspace: Keyspace1
>         Read Count: 60703419
>         Read Latency: 1.1790332096286043 ms.
>         Write Count: 105871791
>         Write Latency: 0.019847457393065166 ms.
>         Pending Tasks: 0
>             Column Family: ColumnFamily1
>             SSTable count: 0
>             Space used (live): 0
>             Space used (total): 0
>             Memtable Columns Count: 0
>             Memtable Data Size: 0
>             Memtable Switch Count: 0
>             Read Count: 0
>             Read Latency: NaN ms.
>             Write Count: 0
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 200000
>             Key cache size: 0
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 0
>             Compacted row maximum size: 0
>             Compacted row mean size: 0
>
>             Column Family: ColumnFamily2
>             SSTable count: 2
>             Space used (live): 482828
>             Space used (total): 482828
>             Memtable Columns Count: 0
>             Memtable Data Size: 0
>             Memtable Switch Count: 3
>             Read Count: 0
>             Read Latency: NaN ms.
>             Write Count: 9
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 200000
>             Key cache size: 0
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 258
>             Compacted row maximum size: 275
>             Compacted row mean size: 266
>
>             Column Family: ColumnFamily3
>             SSTable count: 0
>             Space used (live): 0
>             Space used (total): 0
>             Memtable Columns Count: 0
>             Memtable Data Size: 0
>             Memtable Switch Count: 0
>             Read Count: 0
>             Read Latency: NaN ms.
>             Write Count: 0
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 200000
>             Key cache size: 0
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 0
>             Compacted row maximum size: 0
>             Compacted row mean size: 0
>
>             Column Family: ColumnFamily4
>             SSTable count: 1
>             Space used (live): 19793722
>             Space used (total): 19793722
>             Memtable Columns Count: 306
>             Memtable Data Size: 12731
>             Memtable Switch Count: 3
>             Read Count: 2309
>             Read Latency: NaN ms.
>             Write Count: 3234
>             Write Latency: 0.021 ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 465813
>             Compacted row maximum size: 4784014
>             Compacted row mean size: 3295196
>
>             Column Family: ColumnFamily5
>             SSTable count: 6
>             Space used (live): 364775507
>             Space used (total): 364775507
>             Memtable Columns Count: 14193
>             Memtable Data Size: 552090
>             Memtable Switch Count: 3
>             Read Count: 211451
>             Read Latency: NaN ms.
>             Write Count: 26567
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 187
>             Compacted row maximum size: 333233
>             Compacted row mean size: 662
>
>             Column Family: ColumnFamily6
>             SSTable count: 0
>             Space used (live): 0
>             Space used (total): 0
>             Memtable Columns Count: 0
>             Memtable Data Size: 0
>             Memtable Switch Count: 0
>             Read Count: 0
>             Read Latency: NaN ms.
>             Write Count: 0
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 0
>             Compacted row maximum size: 0
>             Compacted row mean size: 0
>
>             Column Family: ColumnFamily7
>             SSTable count: 12
>             Space used (live): 6031951162
>             Space used (total): 6031951162
>             Memtable Columns Count: 480647
>             Memtable Data Size: 29424092
>             Memtable Switch Count: 43
>             Read Count: 7506944
>             Read Latency: 0.761 ms.
>             Write Count: 3022099
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 239
>             Compacted row maximum size: 93925
>             Compacted row mean size: 2737
>
>             Column Family: ColumnFamily8
>             SSTable count: 1
>             Space used (live): 241104
>             Space used (total): 241104
>             Memtable Columns Count: 2
>             Memtable Data Size: 94
>             Memtable Switch Count: 3
>             Read Count: 685
>             Read Latency: NaN ms.
>             Write Count: 143
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 200000
>             Key cache size: 254
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 254
>             Compacted row maximum size: 479
>             Compacted row mean size: 305
>
>             Column Family: ColumnFamily9
>             SSTable count: 0
>             Space used (live): 0
>             Space used (total): 0
>             Memtable Columns Count: 0
>             Memtable Data Size: 0
>             Memtable Switch Count: 0
>             Read Count: 0
>             Read Latency: NaN ms.
>             Write Count: 0
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 200000
>             Key cache size: 0
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 0
>             Compacted row maximum size: 0
>             Compacted row mean size: 0
>
>             Column Family: ColumnFamily10
>             SSTable count: 3
>             Space used (live): 22874666
>             Space used (total): 22874666
>             Memtable Columns Count: 11886
>             Memtable Data Size: 519166
>             Memtable Switch Count: 3
>             Read Count: 0
>             Read Latency: NaN ms.
>             Write Count: 73970
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 161
>             Compacted row maximum size: 103903
>             Compacted row mean size: 11504
>
>             Column Family: ColumnFamily11
>             SSTable count: 3
>             Space used (live): 6533310
>             Space used (total): 6533310
>             Memtable Columns Count: 8
>             Memtable Data Size: 334
>             Memtable Switch Count: 3
>             Read Count: 5431
>             Read Latency: NaN ms.
>             Write Count: 197
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 200000
>             Key cache size: 653
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 262
>             Compacted row maximum size: 17149
>             Compacted row mean size: 359
>
>             Column Family: ColumnFamily12
>             SSTable count: 1
>             Space used (live): 5504796
>             Space used (total): 5504796
>             Memtable Columns Count: 722
>             Memtable Data Size: 5495928
>             Memtable Switch Count: 3
>             Read Count: 6413
>             Read Latency: NaN ms.
>             Write Count: 5784
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 167
>             Compacted row maximum size: 5498089
>             Compacted row mean size: 261974
>
>             Column Family: ColumnFamily13
>             SSTable count: 3
>             Space used (live): 18208017
>             Space used (total): 18208017
>             Memtable Columns Count: 40
>             Memtable Data Size: 1730
>             Memtable Switch Count: 3
>             Read Count: 4617
>             Read Latency: NaN ms.
>             Write Count: 132
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 200000
>             Key cache size: 1604
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 512
>             Compacted row maximum size: 1776
>             Compacted row mean size: 683
>
>             Column Family: ColumnFamily14
>             SSTable count: 9
>             Space used (live): 1631088415
>             Space used (total): 1631088415
>             Memtable Columns Count: 355843
>             Memtable Data Size: 15750980
>             Memtable Switch Count: 1142
>             Read Count: 37874988
>             Read Latency: 0.830 ms.
>             Write Count: 96285506
>             Write Latency: 0.032 ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 599
>             Compacted row maximum size: 1124
>             Compacted row mean size: 861
>
>             Column Family: ColumnFamily15
>             SSTable count: 2
>             Space used (live): 69991756
>             Space used (total): 69991756
>             Memtable Columns Count: 315483
>             Memtable Data Size: 14827701
>             Memtable Switch Count: 65
>             Read Count: 5653028
>             Read Latency: 6.888 ms.
>             Write Count: 47666
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 160
>             Compacted row maximum size: 5683855
>             Compacted row mean size: 35031
>
>             Column Family: ColumnFamily16
>             SSTable count: 1
>             Space used (live): 44605875
>             Space used (total): 44605875
>             Memtable Columns Count: 20273
>             Memtable Data Size: 645383
>             Memtable Switch Count: 3
>             Read Count: 373155
>             Read Latency: 0.058 ms.
>             Write Count: 199847
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 209
>             Compacted row maximum size: 82030
>             Compacted row mean size: 617
>
>             Column Family: ColumnFamily17
>             SSTable count: 1
>             Space used (live): 5609
>             Space used (total): 5609
>             Memtable Columns Count: 166
>             Memtable Data Size: 2075
>             Memtable Switch Count: 3
>             Read Count: 17630
>             Read Latency: NaN ms.
>             Write Count: 542
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 522
>             Compacted row maximum size: 563
>             Compacted row mean size: 545
>
>             Column Family: ColumnFamily18
>             SSTable count: 3
>             Space used (live): 20705514
>             Space used (total): 20705514
>             Memtable Columns Count: 164
>             Memtable Data Size: 5892
>             Memtable Switch Count: 3
>             Read Count: 5605
>             Read Latency: NaN ms.
>             Write Count: 318
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 200000
>             Key cache size: 2314
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 521
>             Compacted row maximum size: 1239
>             Compacted row mean size: 604
>
>             Column Family: ColumnFamily19
>             SSTable count: 1
>             Space used (live): 29516821
>             Space used (total): 29516821
>             Memtable Columns Count: 8402
>             Memtable Data Size: 268574
>             Memtable Switch Count: 3
>             Read Count: 7587671
>             Read Latency: 0.193 ms.
>             Write Count: 72597
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 186
>             Compacted row maximum size: 18443
>             Compacted row mean size: 270
>
>             Column Family: ColumnFamily20
>             SSTable count: 1
>             Space used (live): 711618
>             Space used (total): 711618
>             Memtable Columns Count: 16
>             Memtable Data Size: 496
>             Memtable Switch Count: 3
>             Read Count: 454
>             Read Latency: NaN ms.
>             Write Count: 97
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 200000
>             Key cache size: 385
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 238
>             Compacted row maximum size: 426
>             Compacted row mean size: 303
>
>             Column Family: ColumnFamily21
>             SSTable count: 6
>             Space used (live): 499913576
>             Space used (total): 499913576
>             Memtable Columns Count: 79019
>             Memtable Data Size: 4820159
>             Memtable Switch Count: 11
>             Read Count: 65780
>             Read Latency: NaN ms.
>             Write Count: 6129833
>             Write Latency: 0.036 ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 278
>             Compacted row maximum size: 288
>             Compacted row mean size: 284
>
>             Column Family: ColumnFamily22
>             SSTable count: 3
>             Space used (live): 378024
>             Space used (total): 378024
>             Memtable Columns Count: 0
>             Memtable Data Size: 0
>             Memtable Switch Count: 0
>             Read Count: 724
>             Read Latency: NaN ms.
>             Write Count: 0
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 0
>             Compacted row maximum size: 0
>             Compacted row mean size: 0
>
>             Column Family: ColumnFamily23
>             SSTable count: 3
>             Space used (live): 11425
>             Space used (total): 11425
>             Memtable Columns Count: 0
>             Memtable Data Size: 0
>             Memtable Switch Count: 1
>             Read Count: 578
>             Read Latency: NaN ms.
>             Write Count: 1
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 0
>             Compacted row maximum size: 0
>             Compacted row mean size: 0
>
>             Column Family: ColumnFamily24
>             SSTable count: 2
>             Space used (live): 20577518
>             Space used (total): 20577518
>             Memtable Columns Count: 306
>             Memtable Data Size: 12731
>             Memtable Switch Count: 3
>             Read Count: 18
>             Read Latency: NaN ms.
>             Write Count: 3234
>             Write Latency: 0.013 ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 465334
>             Compacted row maximum size: 4552398
>             Compacted row mean size: 2815873
>
>             Column Family: ColumnFamily25
>             SSTable count: 1
>             Space used (live): 2888
>             Space used (total): 2888
>             Memtable Columns Count: 2
>             Memtable Data Size: 68
>             Memtable Switch Count: 3
>             Read Count: 1385944
>             Read Latency: NaN ms.
>             Write Count: 19
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache: disabled
>             Row cache: disabled
>             Compacted row minimum size: 223
>             Compacted row maximum size: 234
>             Compacted row mean size: 230
>
>             Column Family: ColumnFamily26
>             SSTable count: 0
>             Space used (live): 0
>             Space used (total): 0
>             Memtable Columns Count: 0
>             Memtable Data Size: 0
>             Memtable Switch Count: 0
>             Read Count: 0
>             Read Latency: NaN ms.
>             Write Count: 0
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 200000
>             Key cache size: 0
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 0
>             Compacted row maximum size: 0
>             Compacted row mean size: 0
>
>     ----------------
>     Keyspace: system
>         Read Count: 14
>         Read Latency: 123.1865 ms.
>         Write Count: 6
>         Write Latency: 0.11666666666666667 ms.
>         Pending Tasks: 0
>             Column Family: LocationInfo
>             SSTable count: 1
>             Space used (live): 2871
>             Space used (total): 2871
>             Memtable Columns Count: 0
>             Memtable Data Size: 0
>             Memtable Switch Count: 2
>             Read Count: 2
>             Read Latency: NaN ms.
>             Write Count: 6
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 1
>             Key cache size: 1
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 203
>             Compacted row maximum size: 554
>             Compacted row mean size: 378
>
>             Column Family: HintsColumnFamily
>             SSTable count: 2
>             Space used (live): 4876356
>             Space used (total): 4876356
>             Memtable Columns Count: 0
>             Memtable Data Size: 0
>             Memtable Switch Count: 0
>             Read Count: 12
>             Read Latency: NaN ms.
>             Write Count: 0
>             Write Latency: NaN ms.
>             Pending Tasks: 0
>             Key cache capacity: 2
>             Key cache size: 2
>             Key cache hit rate: NaN
>             Row cache: disabled
>             Compacted row minimum size: 0
>             Compacted row maximum size: 0
>             Compacted row mean size: 0
>
>
>
>     On 02/28/2012 06:51 PM, Dan Retzlaff wrote:
>>     Hi Stefan. Can you share the output of nodetool cfstats?
>>
>>     On Tue, Feb 28, 2012 at 1:50 AM, Stefan Reek
>>     <stefan@unitedgames.com <mailto:stefan@unitedgames.com>> wrote:
>>
>>         Hi All,
>>
>>         We are running a 3-node cluster with Cassandra 0.6.13.
>>         We are in the process of upgrading to 1.x, but can't do so
>>         for a while because we can't take the cluster offline.
>>         Until now 0.6.13 has run without problems, but lately we are
>>         getting some performance issues.
>>         We are getting timeouts on both reads and writes.
>>         The cluster contains a lot of "old" data which is only read
>>         very occasionally and not written to at all.
>>         Is it possible for this data to negatively impact the
>>         performance of the cluster?
>>         If so, would it help to move this data to another
>>         columnfamily/keyspace?
>>
>>         Cheers,
>>
>>         Stefan
>>
>>
>
>


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