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planner: plan cache support subquery #12945

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Mar 20, 2023
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planner: plan cache support subquery #12945

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d91f303
planner: plan cache support subquery
Oreoxmt Mar 16, 2023
6d5ac91
Apply suggestions from code review
Oreoxmt Mar 17, 2023
b8b3987
add tidb_enable_plan_cache_for_subquery
Oreoxmt Mar 17, 2023
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3 changes: 2 additions & 1 deletion sql-prepared-plan-cache.md
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Expand Up @@ -19,7 +19,8 @@ In the current version of TiDB, if a `Prepare` statement meets any of the follow

- The query contains SQL statements other than `SELECT`, `UPDATE`, `INSERT`, `DELETE`, `Union`, `Intersect`, and `Except`.
- The query accesses partitioned tables or temporary tables, or a table that contains generated columns.
- The query contains sub-queries, such as `select * from t where a > (select ...)`.
- The query contains non-correlated sub-queries, such as `SELECT * FROM t1 WHERE t1.a > (SELECT 1 FROM t2 WHERE t2.b < 1)`.
- The query contains correlated sub-queries with `PhysicalApply` operators in the execution plan, such as `SELECT * FROM t1 WHERE t1.a > (SELECT a FROM t2 WHERE t1.b > t2.b)`.
- The query contains the `ignore_plan_cache` hint, such as `select /*+ ignore_plan_cache() */ * from t`.
- The query contains variables other than `?` (including system variables or user-defined variables), such as `select * from t where a>? and b>@x`.
- The query contains the functions that cannot be cached: `database()`, `current_user`, `current_role`, `user`, `connection_id`, `last_insert_id`, `row_count`, `version`, and `like`.
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8 changes: 8 additions & 0 deletions system-variables.md
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Expand Up @@ -1735,6 +1735,14 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a
- Default value: `ON`
- This variable controls whether Prepared Plan Cache caches execution plans with a variable as the `LIMIT` parameter (`LIMIT ?`). The default value is `ON`, which means Prepared Plan Cache supports caching such execution plans. Note that Prepared Plan Cache does not support caching execution plans with a variable that is greater than 10000.

### tidb_enable_plan_cache_for_subquery <span class="version-mark">New in v7.0.0</span>
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- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- Type: Boolean
- Default value: `ON`
- This variable controls whether Prepared Plan Cache caches queries that contain subqueries.

### tidb_enable_plan_replayer_capture

<CustomContent platform="tidb-cloud">
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