diff --git a/control-execution-plan.md b/control-execution-plan.md index 3249d6f6471d4..3300ebbf2a7dd 100644 --- a/control-execution-plan.md +++ b/control-execution-plan.md @@ -12,12 +12,12 @@ The first two chapters of SQL Tuning introduce how to understand TiDB's executio -Besides the preceding methods, the execution plan is also affected by some system variables. By modifying these variables at the system level or session level, you can control the generation of the execution plan. Starting from v7.1.0, TiDB introduces a relatively special variable [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v657-and-v710). This variable can accept multiple control items to control the behavior of the optimizer in a more fine-grained way, to prevent performance regression caused by behavior changes in the optimizer after cluster upgrade. Refer to [Optimizer Fix Controls](/optimizer-fix-controls.md) for a more detailed introduction. +Besides the preceding methods, the execution plan is also affected by some system variables. By modifying these variables at the system level or session level, you can control the generation of the execution plan. Starting from v6.5.3 and v7.1.0, TiDB introduces a relatively special variable [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v653-and-v710). This variable can accept multiple control items to control the behavior of the optimizer in a more fine-grained way, to prevent performance regression caused by behavior changes in the optimizer after cluster upgrade. Refer to [Optimizer Fix Controls](/optimizer-fix-controls.md) for a more detailed introduction. -Besides the preceding methods, the execution plan is also affected by some system variables. By modifying these variables at the system level or session level, you can control the generation of the execution plan. Starting from v7.1.0, TiDB introduces a relatively special variable [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v657-and-v710). This variable can accept multiple control items to control the behavior of the optimizer in a more fine-grained way, to prevent performance regression caused by behavior changes in the optimizer after cluster upgrade. Refer to [Optimizer Fix Controls](https://docs.pingcap.com/tidb/v7.1/optimizer-fix-controls) for a more detailed introduction. +Besides the preceding methods, the execution plan is also affected by some system variables. By modifying these variables at the system level or session level, you can control the generation of the execution plan. Starting from v6.5.3 and v7.1.0, TiDB introduces a relatively special variable [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v653-and-v710). This variable can accept multiple control items to control the behavior of the optimizer in a more fine-grained way, to prevent performance regression caused by behavior changes in the optimizer after cluster upgrade. Refer to [Optimizer Fix Controls](https://docs.pingcap.com/tidb/v7.1/optimizer-fix-controls) for a more detailed introduction. diff --git a/optimizer-fix-controls.md b/optimizer-fix-controls.md index cc038c4e3aee2..a86e6a5299e27 100644 --- a/optimizer-fix-controls.md +++ b/optimizer-fix-controls.md @@ -14,11 +14,11 @@ Therefore, TiDB provides the Optimizer Fix Controls feature that allows you to m ## Introduction to `tidb_opt_fix_control` -Starting from v7.1.0, TiDB provides the [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v657-and-v710) system variable to control the behavior of the optimizer in a more fine-grained way. +Starting from v6.5.3 and v7.1.0, TiDB provides the [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v653-and-v710) system variable to control the behavior of the optimizer in a more fine-grained way. Each fix is a control item used to adjust the behavior in the TiDB optimizer for one particular purpose. It is denoted by a number that corresponds to a GitHub Issue that contains the technical details of the behavior change. For example, for fix `44262`, you can review what it controls in [Issue 44262](https://github.com/pingcap/tidb/issues/44262). -The [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v657-and-v710) system variable accepts multiple fixes as one value, separated by commas (`,`). The format is `"<#issue1>:,<#issue2>:,...,<#issueN>:"`, where `<#issueN>` is the fix number. For example: +The [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v653-and-v710) system variable accepts multiple fixes as one value, separated by commas (`,`). The format is `"<#issue1>:,<#issue2>:,...,<#issueN>:"`, where `<#issueN>` is the fix number. For example: ```sql SET SESSION tidb_opt_fix_control = '44262:ON,44389:ON'; @@ -26,13 +26,13 @@ SET SESSION tidb_opt_fix_control = '44262:ON,44389:ON'; ## Optimizer Fix Controls reference -### [`44262`](https://github.com/pingcap/tidb/issues/44262) New in v7.1.1 +### [`44262`](https://github.com/pingcap/tidb/issues/44262) New in v6.5.3 and v7.1.1 - Default value: `OFF` - Possible values: `ON`, `OFF` - This variable controls whether to allow the use of [Dynamic pruning mode](/partitioned-table.md#dynamic-pruning-mode) to access the partitioned table when the [GlobalStats](/statistics.md#collect-statistics-of-partitioned-tables-in-dynamic-pruning-mode) are missing. -### [`44389`](https://github.com/pingcap/tidb/issues/44389) New in v7.1.1 +### [`44389`](https://github.com/pingcap/tidb/issues/44389) New in v6.5.3 and v7.1.1 - Default value: `OFF` - Possible values: `ON`, `OFF` @@ -45,10 +45,16 @@ SET SESSION tidb_opt_fix_control = '44262:ON,44389:ON'; - To conserve memory, Plan Cache does not cache queries that exceed a specified number of parameters. - This variable controls the threshold for the maximum number of parameters. `0` means no limit. -### [`44855`](https://github.com/pingcap/tidb/issues/44855) New in v7.1.1 +### [`44830`](https://github.com/pingcap/tidb/issues/44830) New in v6.5.7 - Default value: `OFF` -- Possible values: `ON`、`OFF` +- Possible values: `ON`, `OFF` +- This variable controls whether Plan Cache is allowed to cache execution plans with the `PointGet` operator generated during physical optimization. + +### [`44855`](https://github.com/pingcap/tidb/issues/44855) New in v6.5.4 and v7.1.1 + +- Default value: `OFF` +- Possible values: `ON`, `OFF` - In some scenarios, when the `Probe` side of an `IndexJoin` operator contains a `Selection` operator, TiDB severely overestimates the row count of `IndexScan`. This might cause suboptimal query plans to be selected instead of `IndexJoin`. - To mitigate this issue, TiDB has introduced an improvement. However, due to potential query plan fallback risks, this improvement is disabled by default. - This variable controls whether to enable the preceding improvement. diff --git a/releases/release-7.1.0.md b/releases/release-7.1.0.md index 74a3c2b904387..bed380e7d48e4 100644 --- a/releases/release-7.1.0.md +++ b/releases/release-7.1.0.md @@ -335,7 +335,7 @@ Compared with the previous LTS 6.5.0, 7.1.0 not only includes new features, impr | [`tidb_enable_dist_task`](/system-variables.md#tidb_enable_dist_task-new-in-v710) | Newly added | Controls whether to enable the distributed execution framework. After enabling distributed execution, DDL, import, and other supported backend tasks will be jointly completed by multiple TiDB nodes in the cluster. This variable was renamed from `tidb_ddl_distribute_reorg`. | | [`tidb_enable_non_prepared_plan_cache_for_dml`](/system-variables.md#tidb_enable_non_prepared_plan_cache_for_dml-new-in-v710) | Newly added | Controls whether to enable the [Non-prepared plan cache](/sql-non-prepared-plan-cache.md) feature for DML statements. | | [`tidb_enable_row_level_checksum`](/system-variables.md#tidb_enable_row_level_checksum-new-in-v710) | Newly added | Controls whether to enable the TiCDC data integrity validation for single-row data feature.| -| [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v657-and-v710) | Newly added | This variable provides more fine-grained control over the optimizer and helps to prevent performance regression after upgrading caused by behavior changes in the optimizer. | +| [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v653-and-v710) | Newly added | This variable provides more fine-grained control over the optimizer and helps to prevent performance regression after upgrading caused by behavior changes in the optimizer. | | [`tidb_plan_cache_invalidation_on_fresh_stats`](/system-variables.md#tidb_plan_cache_invalidation_on_fresh_stats-new-in-v710) | Newly added | Controls whether to invalidate the plan cache automatically when statistics on related tables are updated. | | [`tidb_plan_cache_max_plan_size`](/system-variables.md#tidb_plan_cache_max_plan_size-new-in-v710) | Newly added | Controls the maximum size of a plan that can be cached in prepared or non-prepared plan cache. | | [`tidb_prefer_broadcast_join_by_exchange_data_size`](/system-variables.md#tidb_prefer_broadcast_join_by_exchange_data_size-new-in-v710) | Newly added | Controls whether to use the algorithm with the minimum overhead of network transmission. If this variable is enabled, TiDB estimates the size of the data to be exchanged in the network using `Broadcast Hash Join` and `Shuffled Hash Join` respectively, and then chooses the one with the smaller size. [`tidb_broadcast_join_threshold_count`](/system-variables.md#tidb_broadcast_join_threshold_count-new-in-v50) and [`tidb_broadcast_join_threshold_size`](/system-variables.md#tidb_broadcast_join_threshold_size-new-in-v50) will not take effect after this variable is enabled. | diff --git a/sql-non-prepared-plan-cache.md b/sql-non-prepared-plan-cache.md index 020c3b768df43..0a0ec1b4c7066 100644 --- a/sql-non-prepared-plan-cache.md +++ b/sql-non-prepared-plan-cache.md @@ -88,7 +88,7 @@ Due to the preceding risks and the fact that the execution plan cache only provi - Queries that contain numbers or expressions directly after `ORDER BY` or `GROUP BY` are not supported, such as `ORDER BY 1` and `GROUP BY a+1`. Only `ORDER BY column_name` and `GROUP BY column_name` are supported. - Queries that filter on columns of `JSON`, `ENUM`, `SET`, or `BIT` type are not supported, such as `SELECT * FROM t WHERE json_col = '{}'`. - Queries that filter on `NULL` values are not supported, such as `SELECT * FROM t WHERE a is NULL`. -- Queries with more than 200 parameters after parameterization are not supported by default, such as `SELECT * FROM t WHERE a in (1, 2, 3, ... 201)`. Starting from v7.1.1, you can modify this limit using the [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v657-and-v710) system variable. +- Queries with more than 200 parameters after parameterization are not supported by default, such as `SELECT * FROM t WHERE a in (1, 2, 3, ... 201)`. Starting from v7.1.1, you can modify this limit using the [`tidb_opt_fix_control`](/system-variables.md#tidb_opt_fix_control-new-in-v653-and-v710) system variable. - Queries that access partitioned tables, virtual columns, temporary tables, views, or memory tables are not supported, such as `SELECT * FROM INFORMATION_SCHEMA.COLUMNS`, where `COLUMNS` is a TiDB memory table. - Queries with hints or bindings are not supported. - DML statements or `SELECT` statements with the `FOR UPDATE` clause are not supported by default. To remove this restriction, you can execute `SET tidb_enable_non_prepared_plan_cache_for_dml = ON`. diff --git a/system-variables.md b/system-variables.md index 8ba1ce9743547..4e219dc83db1c 100644 --- a/system-variables.md +++ b/system-variables.md @@ -3469,7 +3469,7 @@ mysql> desc select count(distinct a) from test.t; - This variable is used to control whether to enable the [TiFlash late materialization](/tiflash/tiflash-late-materialization.md) feature. Note that TiFlash late materialization does not take effect in the [fast scan mode](/tiflash/use-fastscan.md). - When this variable is set to `OFF` to disable the TiFlash late materialization feature, to process a `SELECT` statement with filter conditions (`WHERE` clause), TiFlash scans all the data of the required columns before filtering. When this variable is set to `ON` to enable the TiFlash late materialization feature, TiFlash can first scan the column data related to the filter conditions that are pushed down to the TableScan operator, filter the rows that meet the conditions, and then scan the data of other columns of these rows for further calculations, thereby reducing IO scans and computations of data processing. -### tidb_opt_fix_control New in v6.5.7 and v7.1.0 +### tidb_opt_fix_control New in v6.5.3 and v7.1.0