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system-variables: add optimizer cost factors #20748

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c053265
planner: add optimizer cost factors
terry1purcell Apr 13, 2025
b286347
Update system-variables.md
terry1purcell Apr 13, 2025
f0502d0
typo
terry1purcell Apr 25, 2025
689ea88
Merge branch 'costfactors' of github.com:terry1purcell/docs into cost…
terry1purcell Apr 25, 2025
27def08
system variables: add v8.5.3 where applicable and revise wording
Oreoxmt Jul 15, 2025
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204 changes: 204 additions & 0 deletions system-variables.md
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Expand Up @@ -4698,6 +4698,210 @@
- 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 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`

### 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`

### 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`

### 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`

### 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`

### 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`

### 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`

### 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`

### 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`

### 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`

### 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`

### 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`

### 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`

### 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`

### 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`

### 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`

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[vale] reported by reviewdog 🐶
[PingCAP.Ambiguous] Consider using a clearer word than 'many' because it may cause confusion.

Raw Output:
{"message": "[PingCAP.Ambiguous] Consider using a clearer word than 'many' because it may cause confusion.", "location": {"path": "system-variables.md", "range": {"start": {"line": 4892, "column": 350}}}, "severity": "INFO"}
### 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`

### tidb_optimizer_selectivity_level

- Scope: SESSION
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