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From Dave Viner <davevi...@pobox.com>
Subject Re: A very short summary on Cassandra for a book
Date Fri, 16 Jul 2010 01:57:46 GMT
I am no expert... but parts seem accurate, parts not.

"Cassandra stores four or five dimension associated arrays"
not sure what you're counting as a dimension of the associated array, but
here are the 2 associative array-like syntaxes:

ColumnFamily[row-key][column-name] = value1
ColumnFamily[row-key][super-column-name][column-name] = value2


"The first dimension is fixed on creation of the database but the rest can
be infinitely large"
I don't understand this sentence.  The definition of a ColumnFamily is set
by the configuration file (storage-conf.xml).  If you change it, and restart
a node, that node will use the new definition of the CF.

It is true that the number of columns can be large.  I have no idea if it's
actually infinite - but more or less.

Also, it's probably not precise to call it a database, since that tends to
invoke images of things like MySQL, Oracle, Postgres, etc.


"Inserts are super fast and can happen to any
database server in the cluster."
Yes, this is true.

"However, the system is append only there so there is no in-place update
operation like increment"
The first part is not quite true.  There is appending, but there is no
increment that's guaranteed universal.  Cassandra is "eventually
consistent".  So atomic increment doesn't really work in the "eventual"
world.  But, more precisely, one can add, update, change, modify, delete
rows, columns, and values at any time from any node.

"Also sorting happens on insert time"
Yes, I believe this is true.

Dave Viner


On Thu, Jul 15, 2010 at 4:26 PM, Karoly Negyesi <chx1975@gmail.com> wrote:

> Hi,
>
> I am writing a scalability chapter in a book and I need to mention
> Apache Cassandra although it's just a mention. Still I would not like
> to be sloppy and would like to get verification whether my summary is
> accurate. "Cassandra stores four or five dimension associated arrays.
> The first dimension is fixed on creation of the database but the rest
> can be infinitely large. Inserts are super fast and can happen to any
> database server in the cluster. However, the system is append only
> there so there is no in-place update operation like increment. Also
> sorting happens on insert time."
>
> Thanks
>
> Karoly Negyesi
>

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