Ahhh, ok, I thought that CQL was just being brought up to date with the functionality already built into composite keys, but I guess I was mistaken there.
But I guess it's just providing a convenient abstraction, using composite column names under the hood. That's where I was confused, thanks. So, in terms of composite column names vs supercolumns: is the only advantage to composite column names that you can do column slicing on subsets of the "subcolumns"? I.e. if I don't mind loading all of the subcolumns for a given supercolumn name in memory at once (since I need them all anyway), is there any disadvantage to using supercolumns here? They seem a little cleaner and more straightforward for my use case, since I don't have the advantage of the CQL composite key thing. Thanks, John On Wed, Mar 14, 2012 at 12:53 PM, Jeremiah Jordan < jeremiah.jor...@morningstar.com> wrote: > Right, so until the new CQL stuff exists to actually query with > something smart enough to know about "composite keys" , You have to define > and query on your own. > > Row Key = UUID > Column = CompositeColumn(string, string) > > You want to then use COLUMN slicing, not row ranges to query the data. > Where you slice in priority as the first part of a Composite Column Name. > > See the "Under the hood and historical notes" section of the blog post. > You want to layout your data per the "Physical representation of the > denormalized timeline rows" diagram. > Where your UUID is the "user_id" from the example, and your priority is > the "tweet_id" > > -Jeremiah > > > ------------------------------ > *From:* John Laban [j...@pagerduty.com] > *Sent:* Wednesday, March 14, 2012 12:37 PM > *To:* user@cassandra.apache.org > *Subject:* Re: Composite keys and range queries > > 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 <aa...@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 <j...@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 >> > >> > >> >> >
