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

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

    [ https://issues.apache.org/jira/browse/CALCITE-3671?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17008724#comment-17008724 ] 

Ruben Q L edited comment on CALCITE-3671 at 1/6/20 10:55 AM:
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Yes, we can do that, but in any case (c) could happen if someone creates their own EnumerableHashJoinRule, or if we carry out CALCITE-3585, that is the reason for the current ticket: even if a complete non-equi HashJoin might be generated, its cost should be accordingly increased so that another (cheaper) option (e.g. NestedLoopJoin) shall be taken.


was (Author: rubenql):
Yes, we can do that, but in any case (c) could happen if someone creates their own EnumerableHashJoinRule, or if we carry out CALCITE-3585

> 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
>            Priority: Major
>
> 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



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