[PROPOSAL]: ZOrderCoveringIndex

[sezruby]

NOTE: This is an issue for tracking Z-order covering index.

The initial implementation is ready in #495.

Problem Statement

Currently, CoveringIndex data is stored as bucketed, and it just sorted within a bucket.
So it is usually less effective for filter queries compared to fully sorted data.
In addition, the index is applied when a given query has conditions only with the first indexed column.

Background and Motivation

TBD

Proposed Solution

Introduce Z-order covering index type to optimize filter query for multiple columns.
TBD

Known/Potential Compatibility Issues

TBD

Design

TBD

Implementation

• CoveringIndex refactoring (Add CoveringIndexTrait and CoveringIndexConfigTrait #516)
• Z-address function (Add ZOrderUDF and ZOrderField for Z-address calculation #517)
• Rules & Filter index (Introduce ZOrderCoveringIndex #518)
• python binding (Add python binding for ZOrderCoveringIndexConfig #519)