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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4851) CQL3: improve support for paginating over composites
Date Mon, 03 Feb 2014 16:10:12 GMT

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Sylvain Lebresne commented on CASSANDRA-4851:
---------------------------------------------

For info, I pushed a dtest too: https://github.com/riptano/cassandra-dtest/commit/da2fb8451b465299c095b320fbfc83c90467a49b

> CQL3: improve support for paginating over composites
> ----------------------------------------------------
>
>                 Key: CASSANDRA-4851
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4851
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Sylvain Lebresne
>            Assignee: Sylvain Lebresne
>            Priority: Minor
>             Fix For: 2.0.6
>
>         Attachments: 4851.txt
>
>
> Consider the following table:
> {noformat}
> CREATE TABLE test (
>     k int,
>     c1 int,
>     c2 int,
>     PRIMARY KEY (k, c1, c2)
> )
> {noformat}
> with the following data:
> {noformat}
> k | c1 | c2
> ------------
> 0 | 0  | 0
> 0 | 0  | 1
> 0 | 1  | 0
> 0 | 1  | 1
> {noformat}
> Currently, CQL3 allows to slice over either c1 or c2:
> {noformat}
> SELECT * FROM test WHERE k = 0 AND c1 > 0 AND c1 < 2
> SELECT * FROM test WHERE k = 0 AND c1 = 1 AND c2 > 0 AND c2 < 2
> {noformat}
> but you cannot express a query that return the 3 last records. Indeed, for that you would
need to do a query like say:
> {noformat}
> SELECT * FROM test WHERE k = 0 AND ((c1 = 0 AND c2 > 0) OR c2 > 0)
> {noformat}
> but we don't support that.
> This can make it hard to paginate over say all records for {{k = 0}} (I'm saying "can"
because if the value for c2 cannot be very large, an easy workaround could be to paginate
by entire value of c1, which you can do).
> For the case where you only paginate to avoid OOMing on a query, CASSANDRA-4415 will
that and is probably the best solution. However, there may be case where the pagination is
say user (as in, the user of your application) triggered.
> I note that one solution would be to add the OR support at least in case like the one
above. That's definitively doable but on the other side, we won't be able to support full-blown
OR, so it may not be very natural that we support seemingly random combination of OR and not
others.
> Another solution would be to allow the following syntax:
> {noformat}
> SELECT * FROM test WHERE k = 0 AND (c1, c2) > (0, 0)
> {noformat}
> which would literally mean that you want records where the values of c1 and c2 taken
as a tuple is lexicographically greater than the tuple (0, 0). This is less SQL-like (though
maybe some SQL store have that, it's a fairly thing to have imo?), but would be much simpler
to implement and probably to use too.



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