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From DuyHai Doan <doanduy...@gmail.com>
Subject Re: CPU consumption of Cassandra
Date Tue, 23 Sep 2014 21:08:51 GMT
I had done some benching in the past when we faced high CPU usage even
though data set is very small, sitting entirely in memory, read the report
there: https://github.com/doanduyhai/Cassandra_Data_Model_Bench

 Our *partial *conclusion were:

 1) slice query fetching a page of 64kb of data and decoding columns is
more CPU-expensive than a single read by column
 2) the decoding of CompositeType costs more CPU for CQL3 data model than
for old Thrift column family
 3) since the Cell type for all CQL3 table is forced to BytesType to
support any type of data, serialization/de-serialization may have a cost on
CPU.

The issue Eric Leleu is facing reminds me of point 1). When he puts limit
to 1, it's a single read by column. The other query with limit 10 is
translated internally to a slice query and may explain the CPU difference

 Now, do not take my words as granted. Those points are just *assumptions *and
partial conclusions. I need extensive in depth debugging to confirm those.
Did not have time lately.

On Tue, Sep 23, 2014 at 10:46 PM, Chris Lohfink <clohfink@blackbirdit.com>
wrote:

> CPU consumption may be affected from the cassandra-stress tool in 2nd
> example as well.  Running on a separate system eliminates it as a possible
> cause.  There is a little extra work but not anything that I think would be
> that obvious.  tracing (can enable with nodetool) or profiling (ie with
> yourkit) can give more exposure to the bottleneck.  Id run test from
> separate system first.
>
> ---
> Chris Lohfink
>
>
> On Sep 23, 2014, at 12:48 PM, Leleu Eric <Eric.Leleu@worldline.com> wrote:
>
> First of all, Thanks for your help ! :)
>
> Here is some details :
>
> With RF=N=2 your essentially testing a single machine locally which isnt
> the best indicator long term
>
> I will  test with more nodes, (4 with RF = 2) but for now I'm limited to 2
> nodes for non technical reason ...
>
> Well, first off you shouldn't run stress tool on the node your testing.
> Give it its own box.
>
> I performed the test in a new Keyspace in order to have a clear dataset.
>
> the 2nd query since its returning 10x the data and there will be more to
> go through within the partition
>
> I configured cassandra-stress in a way of each user has only one bucket so
> the amount of data is the same in the both case. ("select * from buckets
> where name = ? and tenantid = ? limit 1" and "select * from
> owner_to_buckets  where owner = ? and tenantid = ? limit 10").
> Does cassandra perform extra read when the limit is bigger than the
> available data (even if the partition key contains only one single value in
> the clustering column) ?
> If the amount of data is the same, how can we explain the difference of
> CPU consumption?
>
>
> Regards,
> Eric
>
> ________________________________________
> De : Chris Lohfink [clohfink@blackbirdit.com]
> Date d'envoi : mardi 23 septembre 2014 19:23
> À : user@cassandra.apache.org
> Objet : Re: CPU consumption of Cassandra
>
> Well, first off you shouldn't run stress tool on the node your testing.
> Give it its own box.
>
> With RF=N=2 your essentially testing a single machine locally which isnt
> the best indicator long term (optimizations available when reading data
> thats local to the node).  80k/sec on a system is pretty good though, your
> probably seeing slower on the 2nd query since its returning 10x the data
> and there will be more to go through within the partition. 42k/sec is still
> acceptable imho since these are smaller boxes.  You are probably seeing
> high CPU because the system is doing a lot :)
>
> If you want to get more out of these systems can do some tuning probably,
> enable trace to see whats actually the bottleneck.
>
> Collections will very likely hurt more then help.
>
> ---
> Chris Lohfink
>
> On Sep 23, 2014, at 9:39 AM, Leleu Eric <Eric.Leleu@worldline.com<
> mailto:Eric.Leleu@worldline.com <Eric.Leleu@worldline.com>>> wrote:
>
> I tried to run “cassandra-stress” on some of my table as proposed by Jake
> Luciani.
>
> For a simple table, this tool is able to perform 80000 read op/s with a
> few CPU consumption if I request the table by the PK(name, tenanted)
>
> Ex :
> TABLE :
>
> CREATE TABLE IF NOT EXISTS buckets (tenantid varchar,
> name varchar,
> owner varchar,
> location varchar,
> description varchar,
> codeQuota varchar,
> creationDate timestamp,
> updateDate timestamp,
> PRIMARY KEY (name, tenantid));
>
> QUERY : select * from buckets where name = ? and tenantid = ? limit 1;
>
> TOP output for 900 threads on cassandra-stress :
> top - 13:17:09 up 173 days, 21:54,  4 users,  load average: 11.88, 4.30,
> 2.76
> Tasks: 272 total,   1 running, 270 sleeping,   0 stopped,   1 zombie
> Cpu(s): 71.4%us, 14.0%sy,  0.0%ni, 13.1%id,  0.0%wa,  0.0%hi,  1.5%si,
>  0.0%st
> Mem:  98894704k total, 96367436k used,  2527268k free,    15440k buffers
> Swap:        0k total,        0k used,        0k free, 88194556k cached
>
>  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
> 25857 root      20   0 29.7g 1.5g  12m S 693.0  1.6  38:45.58 java  <==
> Cassandra-stress
> 29160 cassandr  20   0 16.3g 4.8g  10m S  1.3  5.0  44:46.89 java  <==
> Cassandra
>
>
>
> Now, If I run another query on a table that provides a list of buckets
> according to the  owner, the number of op/s is divided by 2  (42000 op/s)
> and CPU consumption grow UP.
>
> Ex :
> TABLE :
>
> CREATE TABLE IF NOT EXISTS owner_to_buckets (tenantid varchar,
> name varchar,
> owner varchar,
> location varchar,
> description varchar,
> codeQuota varchar,
> creationDate timestamp,
> updateDate timestamp,
> PRIMARY KEY ((owner, tenantid), name));
>
> QUERY : select * from owner_to_buckets  where owner = ? and tenantid = ?
> limit 10;
>
> TOP output for 4  threads on cassandra-stress:
>
> top - 13:49:16 up 173 days, 22:26,  4 users,  load average: 1.76, 1.48,
> 1.17
> Tasks: 273 total,   1 running, 271 sleeping,   0 stopped,   1 zombie
> Cpu(s): 26.3%us,  8.0%sy,  0.0%ni, 64.7%id,  0.0%wa,  0.0%hi,  1.0%si,
>  0.0%st
> Mem:  98894704k total, 97512156k used,  1382548k free,    14580k buffers
> Swap:        0k total,        0k used,        0k free, 90413772k cached
>
>  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
> 29160 cassandr  20   0 13.6g 4.8g  37m S 186.7  5.1  62:26.77 java <==
> Cassandra
> 50622 root      20   0 28.8g 469m  12m S 102.5  0.5   0:45.84 java <==
> Cassandra-stress
>
> TOP output for 271  threads on cassandra-stress:
>
>
> top - 13:57:03 up 173 days, 22:34,  4 users,  load average: 4.67, 1.76,
> 1.25
> Tasks: 272 total,   1 running, 270 sleeping,   0 stopped,   1 zombie
> Cpu(s): 81.5%us, 14.0%sy,  0.0%ni,  3.1%id,  0.0%wa,  0.0%hi,  1.3%si,
>  0.0%st
> Mem:  98894704k total, 94955936k used,  3938768k free,    15892k buffers
> Swap:        0k total,        0k used,        0k free, 85993676k cached
>
>  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
> 29160 cassandr  20   0 13.6g 4.8g  38m S 430.0  5.1  82:31.80 java <==
> Cassandra
> 50622 root      20   0 29.1g 2.3g  12m S 343.4  2.4  17:51.22 java <==
> Cassandra-stress
>
>
> I have 4 tables with  a composed PRIMARY KEY (two of them has 4 entries :
> 2 for the partition key, one for cluster column and one for sort column)
> Two of these tables are frequently read with the partition key because we
> want to list data of a given user, this should explain my CPU load
> according to the simple test done with Cassandra-stress …
>
> How can I avoid this?
> Collections could be an option but the number of data per user is not
> limited and can easily exceed 200 entries. According to the Cassandra
> documentation, collections have a size limited to 64KB. So it is probably
> not a solution in my case. ☹
>
>
> Regards,
> Eric
>
> De : Chris Lohfink [mailto:clohfink@blackbirdit.com
> <clohfink@blackbirdit.com>]
> Envoyé : lundi 22 septembre 2014 22:03
> À : user@cassandra.apache.org<mailto:user@cassandra.apache.org
> <user@cassandra.apache.org>>
> Objet : Re: CPU consumption of Cassandra
>
> Its going to depend a lot on your data model but 5-6k is on the low end of
> what I would expect.  N=RF=2 is not really something I would recommend.
> That said 93GB is not much data so the bottleneck may exist more in your
> data model, queries, or client.
>
> What profiler are you using?  The cpu on the select/read is marked as
> RUNNABLE but its really more of a wait state that may throw some profilers
> off, it may be a red haring.
>
> ---
> Chris Lohfink
>
> On Sep 22, 2014, at 11:39 AM, Leleu Eric <Eric.Leleu@worldline.com<
> mailto:Eric.Leleu@worldline.com <Eric.Leleu@worldline.com>>> wrote:
>
>
> Hi,
>
>
> I’m currently testing Cassandra 2.0.9  (and since the last week 2.1) under
> some read heavy load…
>
> I have 2 cassandra nodes (RF : 2) running under CentOS 6 with 16GB of RAM
> and 8 Cores.
> I have around 93GB of data per node (one Disk of 300GB with SAS interface
> and a Rotational Speed of 10500)
>
> I have 300 active client threads and they request the C* nodes with a
> Consitency level set to ONE (I’m using the CQL datastax driver).
>
> During my tests I saw  a lot of CPU consumption (70% user / 6%sys / 4%
> iowait / 20%idle).
> C* nodes respond to around 5000 op/s (sometime up to 6000op/s)
>
> I try to profile a node and at the first look, 60% of the CPU is passed in
> the “sun.nio.ch<http://sun.nio.ch/>” package. (SelectorImpl.select or
> Channel.read)
>
> I know that Benchmark results are highly dependent of the Dataset and use
> cases, but according to my point of view this CPU consumption is normal
> according to the load.
> Someone can confirm that point ?
> According to my Hardware configuration, can I expect to have more than
> 6000 read op/s ?
>
>
> Regards,
> Eric
>
>
>
>
>
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> Ce message et les pièces jointes sont confidentiels et réservés à l'usage
> exclusif de ses destinataires. Il peut également être protégé par le secret
> professionnel. Si vous recevez ce message par erreur, merci d'en avertir
> immédiatement l'expéditeur et de le détruire. L'intégrité du message ne
> pouvant être assurée sur Internet, la responsabilité de Worldline ne pourra
> être recherchée quant au contenu de ce message. Bien que les meilleurs
> efforts soient faits pour maintenir cette transmission exempte de tout
> virus, l'expéditeur ne donne aucune garantie à cet égard et sa
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> This e-mail and the documents attached are confidential and intended
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> e-mail in error, please notify the sender immediately and destroy it. As
> its integrity cannot be secured on the Internet, the Worldline liability
> cannot be triggered for the message content. Although the sender endeavours
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