[jira] [Created] (CALCITE-3671) Join cost computation should consider join condition (equi vs non-equi)

["Ruben Q L (Jira)" <ji...@apache.org>]

Ruben Q L created CALCITE-3671:
----------------------------------

             Summary: Join cost computation should consider join condition (equi vs non-equi)
                 Key: CALCITE-3671
                 URL: https://issues.apache.org/jira/browse/CALCITE-3671
             Project: Calcite
          Issue Type: Improvement
    Affects Versions: 1.21.0
            Reporter: Ruben Q L


In some Join algorithms, the actual cost of performing the join would depend on whether or not the join conditions is an equi-join or not, therefore computeSelfCost should reflect that.
This would be the case for example of HashJoin (which now supports all type of join condition, see CALCITE-2973) or MergeJoin (idem, CALCITE-3285).
To sump up, we can have three different scenarios:

a) The condition is a "complete equi-join condition"; this is the best case scenario, the join is performed purely on a hash/merge based algorithm and no extra predicate is required.
b) The condition is a "partial equi-join conditiom", i.e. the condition contains some equi-join items, but also some non-equi-join items; in this case the join is performed on a hash/merge based algorithm (for the equi-join items) + an extra predicate (for the non-equi-join ones).
c) The join condition is a "complete non-equi-join-condition", i.e. there are no equi-join elements to build a hash/merge based solution, so the algorithm is performed based on a predicate which evaluates the whole condition. This is the worst-case scenario, since the Hash/Merge Join actually behaves as a kind of de-facto nested loop join.

Currently, since the condition nature is not evaluated in the computeSelfCost, cases a-b-c would have an equivalent cost; we should reflect somehow that: cost a < cost b < cost c



--
This message was sent by Atlassian Jira
(v8.3.4#803005)