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system variables: add v8.5.3 where applicable and revise wording #1

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119 changes: 85 additions & 34 deletions system-variables.md
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Expand Up @@ -4698,158 +4698,209 @@ SHOW WARNINGS;
- Default value: `OFF`
- This variable is used to control whether to allow `INSERT`, `REPLACE`, and `UPDATE` statements to operate on the `_tidb_rowid` column. This variable can be used only when you import data using TiDB tools.

### tidb_opt_hash_agg_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_hash_agg_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_hash_join_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_hash_join_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_index_join_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_index_join_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_index_lookup_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_index_lookup_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_index_merge_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_index_merge_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_index_reader_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_index_reader_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_index_scan_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_index_scan_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_limit_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_limit_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_merge_join_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_merge_join_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_sort_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_sort_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_stream_agg_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_stream_agg_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_table_full_scan_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_table_full_scan_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_table_range_scan_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_table_range_scan_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_table_reader_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_table_reader_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_table_rowid_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_table_rowid_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_table_tiflash_scan_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_table_tiflash_scan_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_opt_topn_cost_factor <span class="version-mark">New in v9.0.0</span>
### tidb_opt_topn_cost_factor <span class="version-mark">New in v8.5.3 and v9.0.0</span>

> **Warning:**
>
> This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.

- Scope: SESSION | GLOBAL
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): Yes
- Type: Float
- Range: `[0, 2147483647]`
- Default value: `1`
- This variable is internally used in the Cost Model, and it is NOT recommended to modify its value unless directed by TiDB Optimizer Engineering.

### tidb_optimizer_selectivity_level

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