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From John Laban <j...@pagerduty.com>
Subject Re: Composite keys and range queries
Date Wed, 14 Mar 2012 17:37:59 GMT
Hmm, now I'm really confused.

> This may be of use to you
http://www.datastax.com/dev/blog/schema-in-cassandra-1-1

This article is what I actually used to come up with my schema here.  In
the "Clustering, composite keys, and more" section they're using a schema
very similarly to how I'm trying to use it.  They define a composite key
with two parts, expecting the first part to be used as the partition key
and the second part to be used for ordering.

> The hash for (uuid-1 , p1) may be 100 and the hash for (uuid-1, p2) may
be 1 .

Why?  Shouldn't only "uuid-1" be used as the partition key?  (So shouldn't
those two hash to the same location?)

I'm thinking of using supercolumns for this instead as I know they'll work
(where the row key is the uuid and the supercolumn name is the priority),
but aren't composite row keys supposed to essentially replace the need for
supercolumns?

Thanks, and sorry if I'm getting this all wrong,
John



On Wed, Mar 14, 2012 at 12:52 AM, aaron morton <aaron@thelastpickle.com>wrote:

> You are seeing this http://wiki.apache.org/cassandra/FAQ#range_rp
>
> The hash for (uuid-1 , p1) may be 100 and the hash for (uuid-1, p2) may be
> 1 .
>
> You cannot do what you want to. Even if you passed a start of
> (uuid1,<empty>) and no finish, you would not only get rows where the key
> starts with uuid1.
>
> This may be of use to you
> http://www.datastax.com/dev/blog/schema-in-cassandra-1-1
>
> Or you can store all the priorities that are valid for an ID in another
> row.
>
> Cheers
>
> -----------------
> Aaron Morton
> Freelance Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 14/03/2012, at 1:05 PM, John Laban wrote:
>
> > Forwarding to the Cassandra mailing list as well, in case this is more
> of an issue on how I'm using Cassandra.
> >
> > Am I correct to assume that I can use range queries on composite row
> keys, even when using a RandomPartitioner, if I make sure that the first
> part of the composite key is fixed?
> >
> > Any help would be appreciated,
> > John
> >
> >
> >
> > On Tue, Mar 13, 2012 at 12:15 PM, John Laban <john@pagerduty.com> wrote:
> > Hi,
> >
> > I have a column family that uses a composite key:
> >
> > (ID, priority) -> ...
> >
> > Where the ID is a UUID and the priority is an integer.
> >
> > I'm trying to perform a range query now:  I want all the rows where the
> ID matches some fixed UUID, but within a range of priorities.  This is
> supported even if I'm using a RandomPartitioner, right?  (Because the first
> key in the composite key is the partition key, and the second part of the
> composite key is automatically ordered?)
> >
> > So I perform a range slices query:
> >
> > val rangeQuery = HFactory.createRangeSlicesQuery(keyspace, new
> CompositeSerializer, StringSerializer.get, BytesArraySerializer.get)
> > rangeQuery.setColumnFamily(RouteColumnFamilyName).
> >             setKeys( new Composite(id, priorityStart), new Composite(id,
> priorityEnd) ).
> >             setRange( null, null, false, Int.MaxValue )
> >
> >
> > But I get this error:
> >
> > me.prettyprint.hector.api.exceptions.HInvalidRequestException:
> InvalidRequestException(why:start key's md5 sorts after end key's md5.
>  this is not allowed; you probably should not specify end key at all, under
> RandomPartitioner)
> >
> > Shouldn't they have the same md5, since they have the same partition key?
> >
> > Am I using the wrong query here, or does Hector not support composte
> range queries, or am I making some mistake in how I think Cassandra's
> composite keys work?
> >
> > Thanks,
> > John
> >
> >
>
>

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