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Dominique De Vito commented on CASSANDRA-5054:
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In that case, AFAIK, your proposal is about to replace rowkey like (P1, P2) by
rowkey P1 while repeating P2 as 1st part of composite column names.
We didn't followed that idea for 2 reasons:
1) P2 could be quite long (it's unfortunately a string, not a 'long' integer),
we try to avoid to repeat it
2) we wanted some fixed column names (so, without varying P2 as 1st part of a
composite column name) for secondary index goals
So, this new partitioner appeared (IMHO) to us as a better design than wide row.
> new partitioner for rowkey pairs (P1, P2) targeting hierarchical data
> ---------------------------------------------------------------------
>
> Key: CASSANDRA-5054
> URL: https://issues.apache.org/jira/browse/CASSANDRA-5054
> Project: Cassandra
> Issue Type: Improvement
> Components: Contrib, Core
> Reporter: Dominique De Vito
> Priority: Trivial
> Attachments: RandomPartitioner4Pair.java
>
>
> 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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