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From Kasper Middelboe Petersen <>
Subject Re: Datamodel for a highscore list
Date Thu, 23 Jan 2014 08:34:23 GMT
What would the consequence be of having this updated highscore table (using
friendId as part of the clustering index to avoid name collisions):

CREATE TABLE highscore (
  userId uuid,
  score int,
  friendId uuid,
  name varchar,
  PRIMARY KEY(userId, score, friendId)

And then create an index:

CREATE INDEX friendId_idx ON highscore ( friendId );

The table will have many million (I should expect 100+ million) entries.
Each friendId would appear as many times as the user has friends. It sounds
like a scenario where I should take care of using a custom index.

I haven't worked with custom indexes in Cassandra before, but I assume this
would allow me to query the table based on (userId, friendId) for updating

But what would happen in this case? What queries would be affected and
roughly to what degree?

Would this be a viable option?

On Wed, Jan 22, 2014 at 6:44 PM, Kasper Middelboe Petersen <> wrote:

> Hi!
> I'm a little worried about the data model I have come up with for handling
> highscores.
> I have a lot of users. Each user has a number of friends. I need a
> highscore list pr friend list.
> I would like to have it optimized for reading the highscores as opposed to
> setting a new highscore as the use case would suggest I would need to read
> the list a lot more than I would need write new highscores.
> Currently I have the following tables:
> CREATE TABLE user (userId uuid, name varchar, highscore int, bestcombo
> int, PRIMARY KEY(userId))
> CREATE TABLE highscore (userId uuid, score int, name varchar, PRIMARY
> KEY(userId, score, name)) WITH CLUSTERING ORDER BY (score DESC);
> ... and a tables for friends - for the purpose of this mail assume
> everyone is friends with everyone else
> Reading the highscore list for a given user is easy. SELECT * FROM
> highscores WHERE userId = <id>.
> Problem is setting a new highscore.
> 1. I need to read-before-write to get the old score
> 2. I'm screwed if something goes wrong and the old score gets overwritten
> before all the friends highscore lists gets updated - and it is an highly
> visible error due to the same user is on the highscore multiple times.
> I would very much appreciate some feedback and/or alternatives to how to
> solve this with Cassandra.
> Thanks,
> Kasper

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