[IGNITE-21948] Rethink distributed aggregates converter rules.

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: sql
• Labels: ignite-3 perfomance sql
• Assignee: Andrey Mashenkov
• Reporter: Andrey Mashenkov
• Created: 03/Apr/24 13:09
• Updated: 17/Apr/24 08:09

Description

Motivation.

We convert LogicalAggregate to map-reduce unconditionally (if possible), which blows plan search space.
Some plans, which have reduce-phase followed by map-phase without Exchange, make no sense and will be thrown away after applying cost model (if no - there is a bug).

Suggestion.

What if we will emit only plans with colocated aggregates?
We can write rules to pushdown colocated aggregate through Exchange via splitting into map-reduce phases, if colocation can't be preserved.
If Exchange can preserve colocation, then aggregate is pushed gown without splitting.

Let's investigate, if we can eliminate (or significantly decrease number of plans)

1. with Exchange-less Reduce->Map
2. map-reduce aggregates on colocated data.

Issue Links

• relates to: IGNITE-21580 Sql. Unable to optimise query using only two phase aggregates