

Cassandra By Example - angelabartels
http://www.rackspacecloud.com/blog/2010/05/12/cassandra-by-example/

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WesleyJohnson
In each of the two examples he defines a way of tracking both who you're
following and who is following you by implementing two tables in SQL or two
"column stores" in Cassandra.

Why would you need to (or want to) store these separately? A table indicating
User X is following User Y would give you enough to fullfill queries for both
followers and followees.

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strebler
In a database, yes, a single table with two indexes would efficiently look up
followings/followers.

But in Cassandra there is no support for secondary indexes, so the
follower/following data needs to be in separate column families. Then, they
each have an index and can be looked up efficiently. (At least as far as I
understand things in the NoSQL world)

~~~
dagheti
So what happens when you create the follower but not followed index then
realize you need it. Is there a way to create that new ColumnFamily without
writing a object-by-object program that must traverse all the data? I suppose
the concept of data locality doesn't apply, but what is the best way to do
that sort of operation?

~~~
buss
You'd write a MapReduce program to do it. Cassandra 0.6 has full support for
Hadoop.

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nazgulnarsil
I thought this was going to be about engineers trying to warn managers about
impending massive failure and no one listening. the most famous (engineering)
example being Challenger's O-rings.

see Cassandra Complex: <http://en.wikipedia.org/wiki/Cassandra_(metaphor)>

