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From "Tiwari, Dushyant" <Dushyant.Tiw...@morganstanley.com>
Subject Index and schema review
Date Wed, 08 Feb 2012 09:11:34 GMT
Hi Cassandra Users,

I am considering Cassandra as the main data store. Just a quick description of the entity
structure that we are looking at to store/design schema for. So we have 3 entities A,B and
C. A has one to many relationship with B and similar is true for B and C. Hence this gives
us a tree like structure with A as a root. To store this structure in the Cassandra I am looking
at the following col family schema design.


Col Family : For storing A
Id of A - Key
Date - Indexed
Byte format of A object

Col Family : For storing B
Id of B - Key
Date - Indexed field
Id of A to which B belongs - Indexed
Byte format of B object

Col Family : For storing C
Id of C - Key
Date - Indexed field
Id of A to which C belongs - Indexed
Id of B to which C belongs - Indexed
Byte format of C object


Maintaining an index on date because caches are supposed to be preloaded with say 3 days worth
of data. Now the questions are

1.       Are the indexes local? i.e if node 1 holds say 10 keys that will only have indexes
for theses 10 keys. In short - interested in knowing how is the index partitioned?

n  Just to appreciate the concern I have consider the case where we receive 100 keys and we
have 10 Cassandra nodes. Assuming even distribution of 10 keys each node. Will there be 10
partitions of the index on 10 different nodes - only of the keys it owns?


2.       Opinion about the schema design above. To list down the use cases -

n  Preload the processes on start up with 3 days of data. (The data store should hold data
which dates as back as 3 years)

n   Given Id of A get all the B's and C's of the tree.


Hoping to hear soon.

Thanks and Regards,
Dushyant

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