tiflash: support inverted index

[Lloyd-Pottiger]

First-time contributors' checklist

• I've signed Contributor License Agreement that's required for repo owners to accept my contribution.

What is changed, added or deleted? (Required)

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions (in Chinese).

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign overvenus for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[breezewish]

Could you also describe the scenario of the inverted index? As a user, I may want to know in what cases I should build inverted index and in what cases a traditional row index may be preferred. The more examples, the better.

[Lloyd-Pottiger]

Add a section:

## 适用场景

数值列倒排索引在 TiFlash 中构建，支持数值、日期时间类型的 =, !=, >, >=, <, <=, in 快速过滤，在以下场景中数值列倒排索引有明显优势：

- 过滤条件过滤率高，但过滤后行数依然较多。TiFlash 批量读取性能可能优于 TiKV 索引回表。
- 查询包含 IndexMerge 或 IndexJoin 算子，但 TiKV 索引命中行数多导致性能差。将 IndexJoin 转化为 HashJoin，下推到 TiFlash 节点进行计算，利用 MPP 并行降低查询延迟。
- 查询 WHERE 子句同时包含简单等值、范围过滤条件和复杂函数过滤条件。数值列倒排索引帮忙提前过滤掉不满足简单等值、范围过滤条件的行，从而减少复杂函数过滤条件的计算量。