[jira] [Closed] (CALCITE-299) Divide the join graph into partitions that can be optimized separately

["Julian Hyde (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-299?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Julian Hyde closed CALCITE-299.
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    Resolution: Won't Fix

I think we can close this. It's an idea for achieving performance on queries with many joins. The problem seems to be solved adequately by other means. We can always come back and consider this approach in future.

> Divide the join graph into partitions that can be optimized separately
> ----------------------------------------------------------------------
>
>                 Key: CALCITE-299
>                 URL: https://issues.apache.org/jira/browse/CALCITE-299
>             Project: Calcite
>          Issue Type: Bug
>            Reporter: GitHub Import
>            Priority: Major
>              Labels: github-import
>
> Currently Optiq's join optimization is exhaustive. The search space increases combinatorially, so for a query with more than about 8 joins, this is impractical. I propose a "divide and conquer" approach that tames the search space but doesn't cut out the important parts of the search space.
> First, there is a planning phase that gathers together all joins into a single mega relational expression, MultiJoinRel. 
> Then an algorithm builds a join graph, and finds a sub-graph (tree) that minimizes some cost function. Then divide that sub-graph into clusters; the nodes in a cluster are tightly connected, and the links between clusters are relatively loosely connected.
> The output of this algorithm is the graph, partitioned into moderately sized groups of nodes (say 5 - 7 maximum). Typically, in a multi-star query, each group of nodes would have a "fact table" at its center, surrounded by "dimension tables" connected by many-to-one relationships. (Fact table and dimension table are relative terms.)
> We put in place fire walls (maybe a special kind of RelNode) to prevent join transformation rules from working across clusters. Then we invoke the conventional planning process.
> ---------------- Imported from GitHub ----------------
> Url: https://github.com/julianhyde/optiq/issues/299
> Created by: [julianhyde|https://github.com/julianhyde]
> Labels: 
> Created at: Wed Jun 11 23:24:08 CEST 2014
> State: open



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