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From Dathan Pattishall <datha...@gmail.com>
Subject Re: Using this I think I found/verified an interesting problem with Cassandra
Date Wed, 08 Sep 2010 19:32:29 GMT
Ah thanks Jonathan, this is yet again a great explanation to get me started.
Will do some digging. Thanks allot!

On Wed, Sep 8, 2010 at 12:30 PM, Jonathan Ellis <jbellis@gmail.com> wrote:

> it looks to me like you are describing "compaction causes a lot of
> i/o."  see http://wiki.apache.org/cassandra/MemtableSSTable#Compaction
>
> things you can do about the extra i/o:
>  - increase memtable sizes (if you haven't done this yet you should,
> by 10x or so)
>  - reduce compaction priority (see
> http://www.riptano.com/blog/cassandra-annotated-changelog-063)
>  - enable the dynamic snitch (see
> http://www.riptano.com/blog/whats-new-cassandra-065) so other nodes
> can route around one that is slow during a compaction
>
> you can't make it stop using extra space during the compaction itself,
> that is part of the design (and part of the price you pay for not
> doing random i/o at insert time).
>
> On Wed, Sep 8, 2010 at 2:08 PM, Dathan Pattishall <dathanvp@gmail.com>
> wrote:
> > This link describe ganglia / cassandra graphing.
> >
> > http://mysqldba.blogspot.com/2010/09/cassandra-and-ganglia.html
> >
> > I ran into a problem illustrated here.
> >
> > http://www.flickr.com/photos/dathan/4971255111/
> >
> > This screen shot shows a huge spike of transport exceptions between the
> > hours of 12:15 - to 1:30. Why? Lets see.
> >
> > http://www.flickr.com/photos/dathan/4971869002/
> >
> > This link shows that the pending reads jump because the message
> > deserialization pool (mutex) blocks or maybe its viceversa. But Why? Lets
> > see.
> >
> > This link shows that wait_io on the box sky rocketed.
> >
> > http://www.flickr.com/photos/dathan/4971290101/
> >
> > but why?
> >
> > Could it be because
> >
> > http://www.flickr.com/photos/dathan/4971869054/
> >
> > This graph shows a massive amount of data growth for this server, then it
> > reduces but why? How can I tune it so that a growth of data doesn't
> explode
> > like this?
> >
> >
> >
> > Some background information:
> >
> > These servers are DELL 2950 dual quad core boxes with 48GB of Ram on a
> > RAID-10 EXT3 FS backed by 8 disks on a PERC-6 Controller with BBC. Each
> > server rougly recieves 300-400 requests per second fronted by a F5
> > Loadbalancer (soon to be HA-Proxy) on least connections, doing a client
> stat
> > check to verify the server is up from a client point of view.
> >
> > There is only one simple key space. A Super Column is defined but not
> used
> > and uses a RandomPartitioner with NO RowCaching and mmap enabled.
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
>
>
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of Riptano, the source for professional Cassandra support
> http://riptano.com
>

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