tidb: enhance clarity and ensure consistency for the system variable tidb_auto_analyze_concurrency (#20704)

Author: 0xPoe

releases/release-8.4.0.md

@@ -54,7 +54,7 @@ Quick access: [Quick start](https://docs.pingcap.com/tidb/v8.4/quick-start-with-
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     <td><a href="https://docs.pingcap.com/tidb/v8.4/system-variables#tidb_auto_analyze_concurrency-new-in-v840">Concurrent automatic statistics collection</a></td>
-    <td>You can set the concurrency within a single automatic statistics collection task using the system variable <code>tidb_auto_analyze_concurrency</code>. TiDB automatically determines the concurrency of scanning tasks based on node scale and hardware specifications. This improves statistics collection efficiency by fully utilizing system resources, reduces manual tuning, and ensures stable cluster performance.</td>
+    <td>Introduce the system variable <code>tidb_auto_analyze_concurrency</code> to control the number of concurrent auto-analyze operations within a TiDB cluster. TiDB automatically determines the concurrency of scanning tasks based on node scale and hardware specifications. This improves statistics collection efficiency by fully utilizing system resources, reduces manual tuning, and ensures stable cluster performance.</td>
   </tr>
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     <td rowspan="1">SQL</td>
@@ -290,7 +290,7 @@ Quick access: [Quick start](https://docs.pingcap.com/tidb/v8.4/quick-start-with-
 | [`tidb_opt_prefer_range_scan`](/system-variables.md#tidb_opt_prefer_range_scan-new-in-v50) | Modified | Changes the default value from `OFF` to `ON`. For tables with no statistics (pseudo-statistics) or empty tables (zero statistics), the optimizer prefers interval scans over full table scans. |
 | [`tidb_scatter_region`](/system-variables.md#tidb_scatter_region) | Modified | Before v8.4.0, its type is boolean, it only supports `ON` and `OFF`, and the Region of the newly created table only supports table level scattering after it is enabled. Starting from v8.4.0, the `SESSION` scope is added, the type is changed from boolean to enumeration, the default value is changed from `OFF` to null, and the optional values `TABLE` and `GLOBAL` are added. In addition, it now supports cluster-level scattering policy to avoid the TiKV OOM issues caused by uneven distribution of regions during fast table creation in batches.|
 | [`tidb_schema_cache_size`](/system-variables.md#tidb_schema_cache_size-new-in-v800) | Modified | Changes the default value from `0` to `536870912` (512 MiB), indicating that this feature is enabled by default. The minimum value allowed is set to `67108864` (64 MiB). |
-| [`tidb_auto_analyze_concurrency`](/system-variables.md#tidb_auto_analyze_concurrency-new-in-v840)| Newly added | Sets the concurrency within a single automatic statistics collection task. Before v8.4.0, this concurrency is fixed at `1`. To speed up statistics collection tasks, you can increase this concurrency based on your cluster's available resources. |
+| [`tidb_auto_analyze_concurrency`](/system-variables.md#tidb_auto_analyze_concurrency-new-in-v840)| Newly added | Sets the concurrency for auto-analyze operations within a TiDB cluster. Before v8.4.0, this concurrency is fixed at `1`. To speed up statistics collection tasks, you can increase this concurrency based on your cluster's available resources. |
 | [`tidb_enable_instance_plan_cache`](/system-variables.md#tidb_enable_instance_plan_cache-new-in-v840)| Newly added | Controls whether to enable the Instance Plan Cache feature. |
 | [`tidb_enable_stats_owner`](/system-variables.md#tidb_enable_stats_owner-new-in-v840)| Newly added | Controls whether the corresponding TiDB instance can run automatic statistics update tasks. |
 | [`tidb_hash_join_version`](/system-variables.md#tidb_hash_join_version-new-in-v840) | Newly added | Controls whether TiDB uses an optimized version of the Hash Join operator. The default value of `legacy` means that the optimized version is not used. If you set it to `optimized`, TiDB uses the optimized version of the Hash Join operator when executing it to improve Hash Join performance. |
@@ -375,7 +375,7 @@ The following features are planned for deprecation in future versions:
     - Add write control to the [`mysql.tidb_runaway_queries`](/mysql-schema/mysql-schema.md#system-tables-related-to-runaway-queries) log table to reduce overhead caused by a large number of concurrent writes [#54434](https://github.com/pingcap/tidb/issues/54434) @[HuSharp](https://github.com/HuSharp)
     - Support Index Join by default when the inner table has `Selection`, `Projection`, or `Aggregation` operators on it [#47233](https://github.com/pingcap/tidb/issues/47233) @[winoros](https://github.com/winoros)
     - Reduce the number of column details fetched from TiKV for `DELETE` operations in certain scenarios, lowering the resource overhead of these operations [#38911](https://github.com/pingcap/tidb/issues/38911) @[winoros](https://github.com/winoros)
-    - Support setting the concurrency within a single automatic statistics collection task using the system variable `tidb_auto_analyze_concurrency` [#53460](https://github.com/pingcap/tidb/issues/53460) @[hawkingrei](https://github.com/hawkingrei)
+    - Support setting the concurrency for auto-analyze operations within a TiDB cluster using the system variable `tidb_auto_analyze_concurrency` [#53460](https://github.com/pingcap/tidb/issues/53460) @[hawkingrei](https://github.com/hawkingrei)
     - Optimize the logic of an internal function to improve performance when querying tables with numerous columns [#52112](https://github.com/pingcap/tidb/issues/52112) @[Rustin170506](https://github.com/Rustin170506)
     - Simplify filter conditions like `a = 1 AND (a > 1 OR (a = 1 AND b = 2))` to `a = 1 AND b = 2` [#56005](https://github.com/pingcap/tidb/issues/56005) @[ghazalfamilyusa](https://github.com/ghazalfamilyusa)
     - Increase the cost of table scans in the cost model for scenarios with a high risk of suboptimal execution plans, making the optimizer prefer indexes [#56012](https://github.com/pingcap/tidb/issues/56012) @[terry1purcell](https://github.com/terry1purcell)

system-variables.md

@@ -1224,7 +1224,7 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
 - Type: Integer
 - Default value: `1`
 - Range: `[1, 2147483647]`
-- This variable is used to set the concurrency within a single automatic statistics collection task. Before v8.4.0, this concurrency is fixed at `1`. To speed up statistics collection tasks, you can increase this concurrency based on your cluster's available resources.
+- This variable controls the number of concurrent auto-analyze operations that can run in a TiDB cluster. Before v8.4.0, this concurrency is fixed at 1. To accelerate statistics collection tasks, you can increase this concurrency based on the available resources in your cluster.
 
 ### tidb_auto_analyze_end_time
 
@@ -1742,7 +1742,7 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
 - Default value: `0`
 - 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 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.
@@ -3179,7 +3179,7 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified
 
 - This variable is used to set whether to record all SQL statements in the [log](/tidb-configuration-file.md#logfile). This feature is disabled by default. If maintenance personnel needs to trace all SQL statements when locating issues, they can enable this feature.
 
-- If the [`log.general-log-file`](/tidb-configuration-file.md#general-log-file-new-in-v800) configuration item is specified, the general log is written to the specified file separately. 
+- If the [`log.general-log-file`](/tidb-configuration-file.md#general-log-file-new-in-v800) configuration item is specified, the general log is written to the specified file separately.
 
 - The [`log.format`](/tidb-configuration-file.md#format) configuration item enables you to configure the log message format, whether the general log is in a separate file or combined with other logs.