pingcap/tidb

Partial2Mode is not necessary in hash aggregation

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#15,271 建立於 2020年3月10日

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help wantedsig/executiontype/enhancementtype/performance

描述

Feature Request

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

hash aggregation with Coprocessor fetches partial results from storage and runs

  1. Partial2Mode, partial results --> partial results
  2. FinalMode, partial results --> final results

It seems that Partial2Mode is a redundant run, we can remove it for better code and performance.

Describe the feature you'd like:

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

貢獻者指南

技術棧
go
領域
database
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。
3
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。
half day
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。
clear
前置要求
Go programmingTiDB aggregation pipeline
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。
40
研究方向
Investigate TiDB's coprocessor aggregation code, specifically how Partial2Mode and FinalMode are used. Look at the hash aggregation logic to confirm that Partial2Mode is redundant and can be removed without affecting correctness. The relevant files are likely in the coprocessor package. Check if there are any tests that cover this behavior.