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From: Jonathan Ellis <jbellis@gmail.com>
Date: Tue, 9 Mar 2010 07:23:00 -0600
Message-ID: <e06563881003090523r4fab8379uf7dea4031b7579d5@mail.gmail.com>
Subject: Re: schema design question
To: cassandra-user@incubator.apache.org
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On Tue, Mar 9, 2010 at 3:53 AM, Matteo Caprari <matteo.caprari@gmail.com> w=
rote:
> Thanks Jonathan.
>
> Correct if I'm wrong: you are suggesting that each time we receive a new
> row (item, [users]) we do 2 operations:
>
> 1) insert (or merge) this row 'as it is' (item, [users])
> 2) for each user in [users]: insert =A0(user, [item])
>
> Each incoming item is liked by 100 users, so it would be 100 db ops per i=
tem.
> User ids are 20b, so it's about 2k per item sent to the database.

Right.

> At about 10 items/sec, we are looking at 1k db ops/sec or 20k/sec.
>
> Can you make a gross estimate of hardware requirements?

One quad-core node can handle ~14000 inserts per second so you are in
good shape.

> We don't know when the like-ing happened: is there something like
> incremental column names?

You can use insert time, or just use a LexicalUUID.

> Or can I user item_id as column name and a null-ish placeolder as value?

Or that too.

> I share Keith concern: if we use Long as column names, won't we end up
> seeing just one user
> instead of 'all users that liked N items'?

That's true.  So you'd want to use a custom comparator where first 64
bits is the Long and the rest is the userid, for instance.

(Long + something else is common enough that we might want to add it
to the defaults...)

-Jonathan