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From "Jonathan Ellis (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-6048) Add the ability to use multiple indexes in a single query
Date Thu, 17 Oct 2013 09:07:43 GMT


Jonathan Ellis updated CASSANDRA-6048:

         Reviewer: Sylvain Lebresne
    Fix Version/s: 2.1
       Issue Type: New Feature  (was: Improvement)
          Summary: Add the ability to use multiple indexes in a single query  (was: Add CQL3
join data filtering)

This is very interesting.  I'm going to push it over to Sylvain for review, but I have a couple
high level reactions:

# We should improve the "planner" to decide whether to use this automatically rather than
adding new syntax.  (This has the side benefit of allowing Thrift users to benefit as well,
but the main reason is that we shouldn't make users do the query planning for us.)
# This is pretty blatantly new functionality; we shouldn't risk destabilizing 2.0 for it,
let alone 1.2.  Tagging 2.1.  Please rebase to trunk and we'll review from there.

> Add the ability to use multiple indexes in a single query
> ---------------------------------------------------------
>                 Key: CASSANDRA-6048
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Alex Liu
>            Assignee: Alex Liu
>             Fix For: 2.1
>         Attachments: 6048-1.2-branch.txt
> Existing data filtering uses the following algorithm
> {code}
>    1. find best selective predicate based on the smallest mean columns count
>    2. fetch rows for the best selective predicate predicate, then filter the data based
on other predicates left.
> {code}
> So potentially we could improve the performance by
> {code}
>    1.  joining multiple predicates then do the data filtering for other predicates.
>    2.  fine tune the best predicate selection algorithm
> {code}
> For multiple predicate join, it could improve performance if one predicate has many entries
and another predicate has a very few of entries. It means a few index CF read, join the row
keys, fetch rows then filter other predicates
> Another approach is to have index on multiple columns.

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