sys var: clarify the description of tidb_ddl_reorg_max_write_speed (#20527)

Author: hfxsd

system-variables.md

@@ -1708,11 +1708,14 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
 - Scope: GLOBAL
 - Persists to cluster: Yes
 - Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No
-- Type: Integer
+- Type: String
 - Default value: `0`
-- Range: `[0, 1125899906842624]` (the maximum value that can be set is 1 PiB)
+- Range: `[0, 1PiB]`
 - This variable limits the write bandwidth for each TiKV node and only takes effect when index creation acceleration is enabled (controlled by the [`tidb_ddl_enable_fast_reorg`](#tidb_ddl_enable_fast_reorg-new-in-v630) variable). When the data size in your cluster is quite large (such as billions of rows), limiting the write bandwidth for index creation can effectively reduce the impact on application workloads.
-- The default value `0` means no write bandwidth limit. The default unit is bytes per second. You can also set the value in formats such as `'1GiB'` or `'256MiB'`.
+- The default value `0` means no write bandwidth limit. 
+- You can specify the value of this variable either with a unit or without a unit.
+    - When you specify the value without a unit, the default unit is bytes per second. For example, `67108864` represents `64MiB` per second.
+    - When you specify the value with a unit, supported units include KiB, MiB, GiB, and TiB. For example, `'1GiB`' represents 1 GiB per second, and `'256MiB'` represents 256 MiB per second.
 
 ### tidb_ddl_reorg_worker_cnt
 
@@ -1739,7 +1742,7 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
 - Default value: `ON`. Before v8.5.0, the default value is `OFF`.
 - This variable is used to control whether to enable [TiDB Accelerated Table Creation](/accelerated-table-creation.md).
 - Starting from v8.0.0, TiDB supports accelerating table creation by the [`CREATE TABLE`](/sql-statements/sql-statement-create-table.md) statement using `tidb_enable_fast_create_table`.
-- This variable is renamed from the variable [`tidb_ddl_version`](https://docs.pingcap.com/tidb/v7.6/system-variables#tidb_ddl_version-new-in-v760) that is introduced in v7.6.0. Starting from v8.0.0, `tidb_ddl_version` no longer takes effect.
+- This variable is renamed from the variable [`tidb_ddl_version`](https://docs-archive.pingcap.com/tidb/v7.6/system-variables#tidb_ddl_version-new-in-v760) that is introduced in v7.6.0. Starting from v8.0.0, `tidb_ddl_version` no longer takes effect.
 - Starting from TiDB v8.5.0, the accelerated table creation feature is enabled by default for newly created clusters, with `tidb_enable_fast_create_table` set to `ON`. For clusters upgraded from v8.4.0 or earlier versions, the default value of `tidb_enable_fast_create_table` remains unchanged.
 
 ### tidb_default_string_match_selectivity <span class="version-mark">New in v6.2.0</span>
@@ -4270,7 +4273,7 @@ mysql> desc select count(distinct a) from test.t;
 - Default value: `""`
 - This variable is used to control some internal behaviors of the optimizer.
 - The optimizer's behavior might vary depending on user scenarios or SQL statements. This variable provides a more fine-grained control over the optimizer and helps to prevent performance regression after upgrading caused by behavior changes in the optimizer.
-- For a more detailed introduction, see [Optimizer Fix Controls](https://docs.pingcap.com/tidb/v7.2/optimizer-fix-controls).
+- For a more detailed introduction, see [Optimizer Fix Controls](https://docs.pingcap.com/tidb/stable/optimizer-fix-controls).
 
 </CustomContent>
 
@@ -4896,7 +4899,7 @@ SHOW WARNINGS;
 >
 > - Depending on the specific business scenario, enabling this option might cause a certain degree of throughput reduction (average latency increase) for transactions with frequent lock conflicts.
 > - This option only takes effect on statements that need to lock a single key. If a statement needs to lock multiple rows at the same time, this option will not take effect on such statements.
-> - This feature is introduced in v6.6.0 by the [`tidb_pessimistic_txn_aggressive_locking`](https://docs.pingcap.com/tidb/v6.6/system-variables#tidb_pessimistic_txn_aggressive_locking-new-in-v660) variable, which is disabled by default.
+> - This feature is introduced in v6.6.0 by the [`tidb_pessimistic_txn_aggressive_locking`](https://docs-archive.pingcap.com/tidb/v6.6/system-variables#tidb_pessimistic_txn_aggressive_locking-new-in-v660) variable, which is disabled by default.
 
 ### tidb_placement_mode <span class="version-mark">New in v6.0.0</span>