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From Artie Copeland <yeslinux....@gmail.com>
Subject Re: when should new nodes be added to a cluster
Date Mon, 02 Aug 2010 23:05:05 GMT
On Mon, Aug 2, 2010 at 2:39 PM, Aaron Morton <aaron@thelastpickle.com>wrote:

> You may need to provide some more information on how many reads your
> sending to the cluster. Also...
>
> How many nodes do you have in the cluster ?
>

We have a cluster of 4 nodes.


> When you are seeing high response times on one node, what's the load like
> on the others ?
>

They are low and until recently when that node was removed performance would
increase, but as of today the problem appeared to just move to another node
once the original faulty node was removed.


> Is the data load evenly distributed around the cluster ?
>

No it is not it look like this:

Address       Status     Load          Range
     Ring

153186065170709351569621555259205461067
10.4.45.22    Up         60.6 GB
23543694856340775179323589033850348191     |<--|
10.4.45.21    Up         58.67 GB
 64044280785277646901574566535858757214     |   |
10.4.44.22    Down       76.27 GB
 145455238521487150744455174232451506694    |   |
10.4.44.21    Up         67.45 GB
 153186065170709351569621555259205461067    |-->|

the down node is the original culprit.  then once that was down it moved
to 10.4.44.21.  Or setup is using rackaware with the 2 nodes in each switch.
 we tried to use 2 nics one for thrift and one for gossip but couldnt get
that working.  so now we just use on nic for all traffic.

Are your clients connecting to different nodes in the cluster ?
>
> Yes we use Pelops and have all 4 nodes in the pool


> Perhaps that node is somehow out of sync with the others...
>
Dont understand what you mean?


> Anything odd happened in the cluster recently, such as one node going down
> ?
>
Yes the node is a test server so it has gone down to update jvm and
storage-conf setting but only for a short amount of time.


> When was the last time you ran repair?
>
We just ran it today and it didn't have any change.  Almost immediately the
row-read-start goes over 4000

heres what iostats looks like:

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           3.34    0.00    1.00   33.93    0.00   61.73

Device:         rrqm/s   wrqm/s   r/s   w/s   rsec/s   wsec/s avgrq-sz
avgqu-sz   await  svctm  %util
sda               0.00     0.00  0.00  0.00     0.00     0.00     0.00
0.00    0.00   0.00   0.00
sda1              0.00     0.00  0.00  0.00     0.00     0.00     0.00
0.00    0.00   0.00   0.00
sda2              0.00     0.00  0.00  0.00     0.00     0.00     0.00
0.00    0.00   0.00   0.00
sdb             335.50     0.00 70.50  0.00  3248.00     0.00    46.07
0.78   11.01   7.40  52.20
sdc             330.00     0.00 70.00  0.50  3180.00     4.00    45.16
2.10   29.65  13.09  92.30
sdd             310.00     0.00 93.50  0.50  3040.00     8.00    32.43
 33.78  350.13  10.64 100.05
dm-0              0.00     0.00 97.00  0.50  9712.00     4.00    99.65
 38.28  384.30  10.26 100.05

Drives are 3-1TB (sdb - sdd) drives stripped using lvm raid 0 and 1TB (sda)
for commit log

Anything else i can provide that might help diagnose.

Thanx
Artie

>
> Aaron
>
>
> On 03 Aug, 2010,at 06:47 AM, Artie Copeland <yeslinux.now@gmail.com>
> wrote:
>
> i have a question on what are the signs from cassandra that new nodes
> should be added to the cluster.  We are currently seeing long read times
> from the one node that has about 70GB of data with 60GB in one column
> family.  we are using a replication factor of 3.  I have tracked down the
> slow to occur when either row-read-stage or message-deserializer-pool is
> high like atleast 4000.  my systems are 16core, 3 TB, 48GB mem servers.  we
> would like to be able to use more of the server than just 70GB.
>
> The system is a realtime system that needs to scale quite large.  Our
> current heap size is 25GB and are getting atleast 50% row cache hit rates.
>  Does it seem strange that cassandra is not able to handle the work load?
>  We perform multislice gets when reading similar to twissandra does.  this
> is to cut down on the network ops.  Looking at iostat it doesnt appear to
> have alot of queued reads.
>
> What are others seeing when they have to add new nodes?  What data sizes
> are they seeing?  This is needed so we can plan our growth and server
> purchase strategy.
>
> thanx
> Artie
>
> --
> http://yeslinux.org <http://yeslinuxorg>
> http://yestech.org
>
>


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