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From kannan chandrasekaran <ckanna...@yahoo.com>
Subject Re: Few questions regarding cassandra deployment on windows
Date Fri, 10 Sep 2010 03:23:46 GMT
Thanks for the replies.... My comments in Bold...
Kannan



From: Gary Dusbabek <gdusbabek@gmail.com>
To: user@cassandra.apache.org
Sent: Thu, September 9, 2010 5:43:31 AM
Subject: Re: Few questions regarding cassandra deployment on windows

On Tue, Sep 7, 2010 at 17:42, kannan chandrasekaran <ckannanck@yahoo.com> wrote:
> Hi All,
>
> We are currently considering Cassandra for our application.
>
> Platform:
> * a single-node cluster.
> * windows '08
> * 64-bit jvm
>
> For the sake of brevity let,
> Cassandra service =  a single node cassandra server running as an embedded
> service inside a JVM
>
>
> My use cases:
> 1) Start with a schema ( keyspace and set of column families under it) in a
> cassandra service
> 2) Need to be able to replicate the same schema structure (add new
> keyspace/columnfamilies with different names ofcourse).
> 3) Because of some existing limitations in my application, I need to be able
> to write to the keyspace/column-families from a cassandra service and read
> the written changes from a different cassandra service. Both the write and
> the read "cassandra-services" are sharing the same Data directory. I
> understand that the application has to take care of any naming collisions.
>
>
> Couple Questions related to the above mentioned usecases:
> 1) I want to spawn a new JVM and launch Cassandra as an embedded service
> programatically instead of using the startup.bat. I would like to know if
> that is possible and any pointers in that direction would be really helpful.
> ( use-case1)

There are a couple ways to do this.  I've used two of them (tanuki and
objectweb).  Tanuki is better imo.  I've never used it, but Apache
procrun is probably worth checking out.


Someone pointed out 
http://prettyprint.me/2010/02/14/running-cassandra-as-an-embedded-service/ as 
way to start it inside a jvm.. Do you still think tanuki/procrun is needed ?

> 2) I understand that there are provisions for live schema changes in 0.7 (
> thank you guys !!!), but since I cant use a beta version in production, I am
> restricted to 0.6 for now. Is it possible to to support use-case 2 in 0.6.5
> ? More specifically, I am planning to make runtime changes to the
> storage.conf xml file followed by a cassandra service restart

Yes, but this is a manual process and will not scale well.

I agree, but I believe 0.7 solves this problem without a restart . Correct me if 
I am wrong. Any ideas when the 0.7 is set to release ?

> 3) Can I switch the data directory at run-time ?  (use-case 3). In order to
> not disrupt read while the writes are in progress, I am thinking something
> like, copy the existing data-dir into a new location; write to a new data
> directory; once the write is complete; switch pointers and restart the
> cassandra service to read from the new directory to pick up the updated
> changes
>


Pointing two cassandra instances at the same data directory?  This is
a bad idea.  I've never tried it, so I don't know exactly what will
happen, but I imagine you would corrupt your system tables pretty
quickly and your commit log wouldn't be too happy either.  This is a
completely unsupported way of using cassandra.

Noted and will avoid it. But Can you please explain what happens if I write to a 
different location and then copy the keyspace & the system  directories into an 
existing location ? Any ideas if that will work ?

Thank you once again !!!
Gary



      
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