pingcap/tidb

Investigate and propose Adaptive Join

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#14,408 建立於 2020年1月9日

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help wantedsig/executionsig/plannertype/enhancement

描述

Feature Request

Is your feature request related to a problem? Please describe:

Sometimes optimizer need defer the choise of Hash Join or Index Nested loops Join because it does not have a deterministic statistics.

Describe the feature you'd like:

We need someone who is familiar with planner and executor to drive and propose a plan, and see how we can be benefited with Adaptive Join.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

貢獻者指南

技術棧
gosql
領域
backenddatabaseperformance
議題類型
feature
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
5
預計時間有經驗貢獻者完成調查、實作、測試並準備 pull request 的粗略時間範圍。
over 1 week
活動狀態議題目前的可參與程度：新鮮、活躍、陳舊、阻塞或等待維護者輸入。
stale
清晰度議題是否清楚說明預期改動、驗收標準和下一步。
mostly clear
前置要求
TiDB planner knowledgeTiDB executor knowledgeJoin algorithm understandingQuery optimization experience
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
5
研究方向
Research the adaptive join implementations in SQL Server and Oracle as referenced. Investigate TiDB's current planner (e.g., planner/core) and executor (executor) codebase to propose a design for adaptive join that defers join type choice based on runtime statistics. Engage with maintainers on the design proposal before implementation.