sysvars: add tidb_shard_row_id_bits and tidb_pre_split_regions (#…

…18917)

system-variables.md

@@ -3133,6 +3133,16 @@ 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:**
@@ -5272,6 +5282,16 @@ 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:**