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From "Dominique De Vito (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-5054) new partitioner for rowkey pairs (P1, P2) targeting hierarchical data
Date Tue, 11 Dec 2012 13:05:21 GMT


Dominique De Vito updated CASSANDRA-5054:


the new partitioner code
> new partitioner for rowkey pairs (P1, P2) targeting hierarchical data
> ---------------------------------------------------------------------
>                 Key: CASSANDRA-5054
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Contrib, Core
>            Reporter: Dominique De Vito
>            Priority: Trivial
>         Attachments:
> This new partitioner is submitted here both for validation and for proposal to other
Cassandra users (may be this partitioner has its place within Cassandra core, or into some
'contrib' directory).
> This new partitioner is a variant of RandomPartitioner with special token computation
for composite rowkeys of size 2.
> The use case of this partitioner is about rowkeys of hierarchical data, that is, rowkeys
like (directory id, file id).
> This partitioner computes tokens so that rows with same "directory id" have a great chance
to be on the same node: the goal is that, when Cassandra is asked about multiple file ids
for the same directory id, a limited number of nodes should be asked.
> So, in case of a composite rowkey of size 2 like (P1, P2), the partitioner computes the
token as follows: <code>merge(getHighBits(md5(P1)), getLowBits(md5(P2)))</code>.
> In case of a rowkey that is NOT a pair, the partitioner returns the same value than RandomPartitioner.
> This partitioner is expected to be used with Cassandra 1.1 or above.
> Cassandra stores in sstables the pair (token, rowkey). Since v1.1, during a compaction
phase, Cassandra does not sort anymore on token only, but 
> sort on the pair (token, rowkey). So, if a custom partitioner produces token collisions
(that is, multiple rowkeys with the same token), it won't be a pb with v1.1 because, in order
to retrieve a row, Cassandra is going to compare the full pair (token, rowkey).
> As the percent of row collisions for this partitioner is unknown, it's expected to be
used with Cassandra 1.1 or above.

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