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sysvars: add tidb_shard_row_id_bits and tidb_pre_split_regions #18917

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Oct 15, 2024
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sysvars: add tidb_shard_row_id_bits and tidb_pre_split_regions #18917

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sysvars: add tidb_shard_row_id_bits and tidb_pre_split_regions
jackysp Sep 14, 2024
6758285
fix ci
jackysp Sep 14, 2024
0604676
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hfxsd Sep 18, 2024
6c8ac38
Refine wording
lilin90 Oct 8, 2024
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20 changes: 20 additions & 0 deletions system-variables.md
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Expand Up @@ -3159,6 +3159,16 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified
- Range: `[1, 100000]`
- This variable controls the maximum number of execution plans that can be cached by [Non-prepared plan cache](/sql-non-prepared-plan-cache.md).

### tidb_pre_split_regions <span class="version-mark">New in v8.4.0</span>

- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
- Type: Integer
- Default value: `0`
- Range: `[0, 15]`
- This variable is used to set the default number of row split shards for newly created tables. When this variable is set to a non-zero value, TiDB will automatically apply this attribute to tables that allow the use of `PRE_SPLIT_REGIONS` (for example, `NONCLUSTERED` tables) when executing `CREATE TABLE` statements. For more information, see [`PRE_SPLIT_REGIONS`](/sql-statements/sql-statement-split-region.md#pre_split_regions). This variable is typically used in conjunction with [`tidb_shard_row_id_bits`](/system-variables.md#tidb_shard_row_id_bits-new-in-v840) to shard new tables and pre-split the Regions of new tables.

### tidb_generate_binary_plan <span class="version-mark">New in v6.2.0</span>

> **Note:**
Expand Down Expand Up @@ -5271,6 +5281,16 @@ SHOW WARNINGS;
- Range: `[1, 9223372036854775807]`
- This variable controls the maximum number of continuous IDs to be allocated for the [`AUTO_RANDOM`](/auto-random.md) or [`SHARD_ROW_ID_BITS`](/shard-row-id-bits.md) attribute. Generally, `AUTO_RANDOM` IDs or the `SHARD_ROW_ID_BITS` annotated row IDs are incremental and continuous in one transaction. You can use this variable to solve the hotspot issue in large transaction scenarios.

### tidb_shard_row_id_bits <span class="version-mark">New in v8.4.0</span>

- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
- Type: Integer
- Default value: `0`
- Range: `[0, 15]`
- This variable is used to set the default number of row ID shards for newly created tables. When this variable is set to a non-zero value, TiDB will automatically apply this attribute to tables that allow the use of `SHARD_ROW_ID_BITS` (for example, `NONCLUSTERED` tables) when executing `CREATE TABLE` statements. For more information, see [`SHARD_ROW_ID_BITS`](/shard-row-id-bits.md).

### tidb_simplified_metrics

> **Note:**
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