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From "Hiller, Dean" <Dean.Hil...@nrel.gov>
Subject Re: Composite Column Query Modeling
Date Fri, 14 Sep 2012 15:42:28 GMT
There is another trick here.  On the playOrm open source project, we need to do a sparse query
for a join and so we send out 100 async requests and cache up the java "Future" objects and
return the first needed result back without waiting for the others.  With the S-SQLin playOrm,
we have the IN clause coming soon as well in which we will use the same technique so as you
iterate over the 1, 3, 29, 56 rows, results may still be coming in as it only blocks if it
gets to 3 and the result for 3 has not come back yet.

Anyways, just an option.  (ps. This option helps us query a 1,000,000 row partition in 60ms
;) and we still haven't added the lookahead cursors which should speed some systems up as
well as it fetches stuff while you are working on the first batch of results)

Later,
Dean

From: Adam Holmberg <adam.holmberg.list@gmail.com<mailto:adam.holmberg.list@gmail.com>>
Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Date: Friday, September 14, 2012 9:08 AM
To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Subject: Re: Composite Column Query Modeling

I think what you're describing might give me what I'm after, but I don't see how I can pass
different column slices in a multiget call. I may be missing something, but it looks like
you pass multiple keys but only a singular SlicePredicate. Please let me know if that's not
what you meant.

I'm aware of CQL3 collections, but I don't think they quite suite my needs in this case.

Thanks for the suggestions!

Adam

On Fri, Sep 14, 2012 at 1:56 AM, aaron morton <aaron@thelastpickle.com<mailto:aaron@thelastpickle.com>>
wrote:
You _could_ use one wide row and do a multiget against the same row for different column slices.
Would be less efficient than a single get against the row. But you could still do big contiguous
column slices.

You may get some benefit from the collections in CQL 3 http://www.datastax.com/dev/blog/cql3_collections

Hope that helps.


-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 14/09/2012, at 8:31 AM, Adam Holmberg <adam.holmberg.list@gmail.com<mailto:adam.holmberg.list@gmail.com>>
wrote:

I'm modeling a new application and considering the use of SuperColumn vs. Composite Column
paradigms. I understand that SuperColumns are discouraged in new development, but I'm pondering
a query where it seems like SuperColumns might be better suited.

Consider a CF with SuperColumn layout as follows

t = {
  k1: {
    s1: { c1:v1, c2:v2 },
    s2: { c1:v3, c2:v4 },
    s3: { c1:v5, c2:v6}
    ...
  }
  ...
}

Which might be modeled in CQL3:

CREATE TABLE t (
  k text,
  s text,
  c1 text,
  c2 text,
  PRIMARY KEY (k, s)
);

I know that it is possible to do range slices with either approach. However, with SuperColumns
I can do sparse slice queries with a set (list) of column names as the SlicePredicate. I understand
that the composites API only returns contiguous slices, but I keep finding myself wanting
to do a query as follows:

SELECT * FROM t WHERE k = 'foo' AND s IN (1,3);

The question: Is there a recommended technique for emulating sparse column slices in composites?

One suggestion I've read is to get the entire range and filter client side. This is pretty
punishing if the range is large and the second keys being queried are sparse. Additionally,
there are enough keys being queried that calling once per key is undesirable.

I also realize that I could manually composite k:s as the row key and use multiget, but this
gives away the benefit of having these records proximate when range queries are used.

Any input on modeling/query techniques would be appreciated.

Regards,
Adam Holmberg


P.S./Sidebar:
--------------------
What this seems like to me is a desire for 'multiget' at the second key level analogous to
multiget at the row key level. Is this something that could be implemented in the server using
SlicePredicate.column_names? Is this just an implementation gap, or is there something technical
I'm overlooking?



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