Partitioning is only done for row keys, the part in your message about keys
and partitioning is correct.
There is no partitioning for columns, all columns for a particular key are
stored on the same node (plus
replicas, of course, which are stored on different nodes). The CompareWith
option for column families
only affects the ordering of columns/supercolumns, not the partitioning.
Cheers,
Martin
________________________________
From: Olivier Mallassi [mailto:omalla...@octo.com]
Sent: Monday, May 10, 2010 1:17 PM
To: user@cassandra.apache.org
Subject: trying to make my ideas clear about partionning...
Hi all,
I am trying to make my ideas clear about how the partioning works in
Cassandra.
Here is what I understood, pease correct me if I am wrong.
- Row key are partitionned based on the partitionning strategy you
choose (randon, order preserving, custom if you implemented the IPartioner
interface). One partionning strategy is defined per cluster (in fact for each
node of the cluster but the confifguration should be the sames so...)
Order Preserving Partionning is better for range queries because the
key are stored in a sequential way so when selecting a range of keys, you hit
less nodes than with the RandomPartitioner.
- Once this first partitioning is done, a second one is done based on
the Column (or SuperColumn) name and the CompareWith you defined for the
ColumnFamily.
Am I right?
Am I wrong if I say that potentially the different columns of the same
ColumnFamily are stored on different nodes? So if I wanna read a complete row,
I hit several nodes.
Is there a way of controlling the way Column are stored?
Thanks for your help.
Oliv/
