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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9231) Support Routing Key as part of Partition Key
Date Fri, 24 Apr 2015 08:44:40 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9231?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14510656#comment-14510656
] 

Sylvain Lebresne commented on CASSANDRA-9231:
---------------------------------------------

If we do this, I have a strong preference for exposing it as a way to define a custom function
for computing the token. So the example above would be written something like:
{noformat}
CREATE FUNCTION myCustomHash(a int, b int) RETURNS bigint AS 'return murmur3(a)';

CREATE TABLE foo (
    a int,
    b int,
    c int,
    d int,
    PRIMARY KEY ((a, b), c)
) WITH tokenizer=myCustomHash;
{noformat}

That's imo more generic and I don't like adding a notion of "routing key" when we already
have "primary key" and "partition key" which is enough "key" (and internally the "routing
key" is really just the token, so no point in having a new notion).

> Support Routing Key as part of Partition Key
> --------------------------------------------
>
>                 Key: CASSANDRA-9231
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9231
>             Project: Cassandra
>          Issue Type: Wish
>          Components: Core
>            Reporter: Matthias Broecheler
>             Fix For: 3.1
>
>
> Provide support for sub-dividing the partition key into a routing key and a non-routing
key component. Currently, all columns that make up the partition key of the primary key are
also routing keys, i.e. they determine which nodes store the data. This proposal would give
the data modeler the ability to designate only a subset of the columns that comprise the partition
key to be routing keys. The non-routing key columns of the partition key identify the partition
but are not used to determine where to store the data.
> Consider the following example table definition:
> CREATE TABLE foo (
>   a int,
>   b int,
>   c int,
>   d int,
>   PRIMARY KEY  (([a], b), c ) );
> (a,b) is the partition key, c is the clustering key, and d is just a column. In addition,
the square brackets identify the routing key as column a. This means that only the value of
column a is used to determine the node for data placement (i.e. only the value of column a
is murmur3 hashed to compute the token). In addition, column b is needed to identify the partition
but does not influence the placement.
> This has the benefit that all rows with the same routing key (but potentially different
non-routing key columns of the partition key) are stored on the same node and that knowledge
of such co-locality can be exploited by applications build on top of Cassandra.
> Currently, the only way to achieve co-locality is within a partition. However, this approach
has the limitations that: a) there are theoretical and (more importantly) practical limitations
on the size of a partition and b) rows within a partition are ordered and an index is build
to exploit such ordering. For large partitions that overhead is significant if ordering isn't
needed.
> In other words, routing keys afford a simple means to achieve scalable node-level co-locality
without ordering while clustering keys afford page-level co-locality with ordering. As such,
they address different co-locality needs giving the data modeler the flexibility to choose
what is needed for their application.



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