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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7850) Composite Aware Partitioner
Date Sat, 30 Aug 2014 22:03:53 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7850?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14116568#comment-14116568
] 

Jonathan Ellis commented on CASSANDRA-7850:
-------------------------------------------

Doing multiget to a single server is negligibly more efficient than doing it to the same number
of partitions across multiple servers.

> Composite Aware Partitioner
> ---------------------------
>
>                 Key: CASSANDRA-7850
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7850
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Drew Kutcharian
>
> Since C* supports composites for partition keys, I think it'd be useful to have the ability
to only use first (or first few) components of the key to calculate the token hash.
> A naive use case would be multi-tenancy:
> Say we have accounts and accounts have users. So we would have the following tables:
> {code}
> CREATE TABLE account (
>   id                     timeuuid PRIMARY KEY,
>   company         text
> );
> {code}
> {code}
> CREATE TABLE user (
>   id              timeuuid PRIMARY KEY, 
>   accountId timeuuid,
>   email        text,
>   password text
> );
> {code}
> {code}
> // Get users by account
> CREATE TABLE user_account_index (
>   accountId  timeuuid,
>   userId        timeuuid,
>   PRIMARY KEY(acid, id)
> );
> {code}
> Say we want to get all the users that belong to an account. We would first have to get
the results from user_account_index and then use a multi-get (WHERE IN) to get the records
from user table. Now this multi-get part could potentially query a lot of different nodes
in the cluster. It’d be great if there was a way to limit storage of users of an account
to a single node so that way multi-get would only need to query a single node.
> With this improvement we would be able to define the user table like so:
> {code}
> CREATE TABLE user (
>   id              timeuuid, 
>   accountId timeuuid,
>   email        text,
>   password text,
>   PRIMARY KEY(((accountId),id))  //extra parentheses
> );
> {code}
> I'm not too sure about the notation, it could be something like PRIMARY KEY(((accountId),id))
where the "(accountId)" means use this part to calculate the hash and ((accountId),id) is
the actual partition key.
> The main complication I see with this is that we would have to use the table definition
when calculating hashes so we know what components of the partition keys need to be used for
hash calculation.



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