pingcap/tidb

The heavy predicates may not need to be pushed down.

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#14,608 建立於 2020年2月3日

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help wantedsig/plannertype/enhancement

描述

For example, a big CASE...WHEN... clause may consume a lot of resources. In this case, push it down to table side may be worse than not pushing it.

We should control its behavior by

  • A hint to disable all predicates of one WHERE clause.
  • A cost-based or a heuristic method to control the predicates automatically.

貢獻者指南

技術棧
gosql
領域
backenddatabaseperformance
議題類型
performance
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。
4
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。
needs investigation
前置要求
Go programmingSQL query optimizationDatabase internalsTiDB optimizer architecture
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。
20
研究方向
Investigate the predicate pushdown logic in TiDB's optimizer, specifically in the planner package. Review the current heuristic for pushdown and identify heavy predicates like CASE...WHEN. Propose a cost model or hint mechanism to skip pushdown for resource intensive clauses.