best practices: multi-column index optimization #20955
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Hello @hfxsd, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
Summary of Changes
Hello! Gemini here, providing a summary of this pull request for author @hfxsd and reviewers. This PR introduces a new documentation page focused on advanced techniques for optimizing queries using multi-column indexes in TiDB. The document explains the fundamentals of multi-column indexes, how TiDB's optimizer derives efficient index ranges, and specifically details how it handles complex query conditions involving both disjunctive (OR) and conjunctive (AND) predicates. It also highlights how TiDB's approach differs from and offers advantages over traditional databases like MySQL in this area.
Highlights
- New Documentation Page: Adds a comprehensive guide on advanced multi-column index optimization in TiDB.
- Index Range Derivation: Explains how the TiDB optimizer generates efficient index ranges based on query conditions and index columns.
- Handling OR Conditions: Details how TiDB processes disjunctive predicates, including merging or keeping separate index ranges for overlapping or non-overlapping conditions, respectively.
- Handling AND Conditions: Describes how TiDB handles conjunctive predicates and complex row expressions by translating them and deriving combined index ranges.
- TiDB vs. MySQL Comparison: Compares TiDB's advanced multi-column index capabilities, particularly its ability to handle complex conditions and range operations, to MySQL.
Changelog
- best-practices/multi-column-index-optimization.md
- Added a new document covering advanced multi-column index optimization.
- Includes sections on background, sample data, optimized queries, index range derivation, handling of OR conditions (lines 126-186), and handling of AND conditions (lines 188-257).
- Provides SQL examples and
EXPLAIN FORMAT=BRIEFoutput to illustrate concepts (e.g., lines 30-41, 80-101, 139-154, 166-183, 239-253). - Compares TiDB's approach to MySQL (lines 255-257, 260-261).
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Code Review
This is a well-written and informative document on advanced multi-column index optimization in TiDB. The explanations are clear, and the examples effectively illustrate the concepts. I have a few suggestions to further enhance its clarity, consistency, and adherence to the style guide.
Summary of Findings
- Style Guide Adherence: Several minor adjustments are suggested to align more closely with the style guide, including using the second person ('you'), expanding contractions, consistent SQL keyword casing, and heading formatting.
- Clarity of Examples: Replacing query labels like
"Q1"with descriptive comments in SQL examples would improve clarity for readers. - Spelling: A minor spelling error was found ("comparision" instead of "comparison").
- Consistency: Ensuring consistent use of backticks for inline code elements like column names (
a1) and consistent casing for SQL keywords (EXPLAIN) will improve readability.
Merge Readiness
The document is well-structured and provides valuable information. The suggested changes are mostly minor and aim to enhance clarity, consistency, and adherence to the style guide. Addressing these points would further polish this excellent contribution. I am unable to approve the pull request myself, but I recommend that these changes be considered before merging.
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[APPROVALNOTIFIER] This PR is NOT APPROVED This pull-request has been approved by: The full list of commands accepted by this bot can be found here.
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| +-----------------------------+---------+-----------+----------------------------------- | ||
| | IndexLookUp | root | | ||
| | ├─IndexRangeScan(Build) | table:listings, | range: | ||
| | index:idx_city_bedrooms_price| ["San Francisco" 2 -inf, |
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Missing a "|' at the beginning
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Should we add the version (which can support this feature) in the document? |
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Co-authored-by: Lilian Lee <[email protected]>
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First-time contributors' checklist
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.
What is the related PR or file link(s)?
Do your changes match any of the following descriptions?