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From Tomer B <tomer...@gmail.com>
Subject Re: Knowing when there is a *real* need to add nodes
Date Wed, 18 May 2011 07:50:35 GMT
As for static disk usage i would add this:

test: df -kh
description: run test after compaction (check GCGraceSeconds in
storage-conf.xml) as only then data is expunged permanently, run on data
disk, assuming here commitlog disk is separated from data dir.
green gauge: used_space < 30% of disk capacity
yellow gauge: used space 30% - 50% of disk capacity
red gauge: used_space > 50% of disk capacity
comments: Compactions can require up to 100% of in use space temporarily in
worst case (data file dir) when approaching 50% or more of disk capacity use
raid0 for data dir disk if cannot try increasing your disk if cannot
consider adding nodes (or first consider adding nodes if that's what you
wish).

2011/5/12 Watanabe Maki <watanabe.maki@gmail.com>

> It's interesting topic for me too.
> How about to add measurement on static disk utilization (% used) and memory
> utilization ( rss, JVM heap, JVM GC )?
>
> maki
>
> From iPhone
>
>
> On 2011/05/12, at 0:49, Tomer B <tomerbd1@gmail.com> wrote:
>
> > Hi
> >
> > I'm trying to predict when my cluster would soon be needing new nodes
> > added, i want a continuous graph telling my of my cluster health so
> > that when i see my cluster becomes more and more busy (I want numbers
> > & measurments) i would be able to know i need to start purchasing more
> > machines and get them into my cluster, so i want to know of that
> > beforehand.
> > I'm writing here what I came with after doing some research over net.
> > I would highly appreciate any additional gauge measurements and ranges
> > in order to test my cluster health and to know beforehand when i'm
> > going to soon need more nodes.Although i'm writing down green
> > gauge,yellow gauge,red gauge, i'm also trying to find a continuous
> > graph where i can tell where our cluster stand (as much as
> > possible...)
> >
> > Also my recommendation is always before adding new nodes:
> >
> > 1. Make sure all nodes are balanced and if not balance them.
> > 2. Separate commit log drive from data (SSTables) drive
> > 3. use mmap index only in memory and not auto
> > 4. Increase disk IO if possible.
> > 5. Avoid swapping as much as possible.
> >
> >
> > As for my gauge tests for when to add new nodes:
> >
> > test: nodetool tpstats -h <cassandra_host>
> > green gauge: No pending column with number higher
> > yellow gauge: pending columns 100-2000
> > red gauge:Larger than 3000
> >
> > test: iostat -x -n -p -z 5 10  and iostat -xcn 5
> > green gauge: kw/s + kr/s reaches is below 25% capacity of disk io
> > yellow gauge: 20%-50%
> > red gauge: 50%+
> >
> > test: ostat -x -n -p -z 5 10 and check %b column
> > green gauge: less than 10%
> > yellow gauge:  10%-80%
> > red gauge: 90%+
> >
> > test: nodetool cfstats --host localhost
> > green gauge: “SSTable count” item does not continually grow over time
> > yellow gauge:
> > red gauge: “SSTable count” item continually grows over time
> >
> > test: ./nodetool cfstats --host localhost | grep -i pending
> > green gauge: 0-2
> > yellow gauge: 3-100
> > red gauge: 101+
> >
> > I would highly appreciate any additional gauge measurements and ranges
> > in order to test my cluster health and to know ***beforehand*** when
> > i'm going to soon need more nodes.
>

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