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From "Marie-Anne" <maharkn...@comcast.net>
Subject RE: OrderPreservingPartitioner for get_range_slices
Date Thu, 16 Sep 2010 00:54:57 GMT
I have tried twice to remove myself from this listserv by following the
directions I received when I signed up.  Can anyone help me?

Marie-Anne

 

From: Phil Stanhope [mailto:stanhope@gmail.com] 
Sent: Wednesday, September 15, 2010 12:43 PM
To: user@cassandra.apache.org
Subject: Re: OrderPreservingPartitioner for get_range_slices

 

My experience for the last question is ... it depends. If you have NO
changes to the store (which I would argue could be abnormal, it's not in a
production  environment allowing writes) ... then I you can do a full
range/key scan and get no repeats. Factors that will impact scanning all
keys include replication factor, actual partitioning, and status of
replications.

 

If you are taking changes while scanning ... what exactly is the semantics
of the key scan that you'd expect? For example, would it be acceptable to
have a "low" key not be returned because it was in the data store before the
full scan ended but you've already gone past that key in your iteration? 

 

I think that these questions apply to both ordered and random partitioners.

 

On Wed, Sep 15, 2010 at 3:30 PM, Michal August├Żn <augustyn.michal@gmail.com>
wrote:

And what about uniqueness? Can we be sure that we get each row just once?

 

Thanks.

2010/9/15 Janne Jalkanen <Janne.Jalkanen@ecyrd.com>

 


Correct. You can use get_range_slices with RandomPartitioner too, BUT the
iteration order is non-predictable, that is, you will not know in which
order you get the rows (RandomPartitioner would probably better be called
ObscurePartitioner - it ain't random, but it's as good as if it were ;-).
This I find to be mostly useful when you want to go through your entire
keyspace, like when doing something map-reduce like.  Or you just have a
fairly small CF.

/Janne



On Sep 15, 2010, at 20:26 , Rana Aich wrote:

Hi All,

I was under the impression that in order to query with get_range_slices one
has to have a OrderPreservingPartitioner.

Can we do get_range_slices with RandomPartitioner also? I can distinctly
remember I read that(OrderPreservingPartitioner for get_range_slices) in
Cassnadra WIKI but now somehow I'm not finding it anymore.

Can anyone throw some light on it.

Thanks and Regards,

Rana

 

 

 


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