[Doc] Doc for shared-data tablet parallel Scan (backport #47458)

docs/en/reference/System_variable.md

@@ -296,6 +296,27 @@ This variable is supported from v2.5.18 and v3.1.7.
 
   Default value: `false`, which means the system selects a replica for each query. This feature is supported since 2.5.6, 3.0.8, and 3.1.4.
 
+### tablet_internal_parallel_mode
+
+* **Description**: Internal Parallel Scan strategy of tablets. Valid Values:
+  * `auto`: When the number of Tablets to be scanned on BE or CN nodes is less than the Degree of Parallelism (DOP), the system automatically determines whether Parallel Scan is needed based on the estimated size of the Tablets.
+  * `force_split`: Forces the splitting of Tablets and performs Parallel Scan.
+* **Default**: auto
+* **Data type**: String
+* **Introduced in**: v2.5.0
+
+### enable_scan_datacache
+
+* **Description**: Specifies whether to enable the Data Cache feature. After this feature is enabled, StarRocks caches hot data read from external storage systems into blocks, which accelerates queries and analysis. For more information, see [Data Cache](../data_source/data_cache.md). In versions prior to 3.2, this variable was named as `enable_scan_block_cache`.
+* **Default**: false
+* **Introduced in**: v2.5
+
+### enable_populate_datacache
+
+* **Description**: Specifies whether to cache data blocks read from external storage systems in StarRocks. If you do not want to cache data blocks read from external storage systems, set this variable to `false`. Default value: true. This variable is supported from 2.5. In versions prior to 3.2, this variable was named as `enable_scan_block_cache`.
+* **Default**: true
+* **Introduced in**: v2.5
+
 ### enable_global_runtime_filter
 
   Whether to enable global runtime filter (RF for short). RF filters data at runtime. Data filtering often occurs in the Join stage. During multi-table joins, optimizations such as predicate pushdown are used to filter data, in order to reduce the number of scanned rows for Join and the I/O in the Shuffle stage, thereby speeding up the query.

docs/zh/reference/System_variable.md

@@ -253,6 +253,15 @@ group-by-count-distinct 查询中为 count distinct 列设置的分桶数。该
 
 默认值：`false`，表示使用原来的机制，即每次查询会从多个副本中选择一个。自 2.5.6、3.0.8、3.1.4 版本起，StarRocks 支持该参数。
 
+### tablet_internal_parallel_mode
+
+* 描述：Tablet 内部并行 Scan 策略。有效值:
+  * `auto`: 在 BE 或 CN 节点需要扫描的 Tablet 数小于 DOP 时，系统根据预估的 Tablet 大小自动判断是否需要并行 Scan。
+  * `force_split`: 强制对 Tablet 进行拆分和并行扫描。
+* 默认值：auto
+* 类型：String
+* 引入版本：v2.5.0
+
 ### enable_scan_block_cache（2.5 及以后）
 
 是否开启 Data Cache 特性。该特性开启之后，StarRocks 通过将外部存储系统中的热数据缓存成多个 block，加速数据查询和分析。更多信息，参见 [Data Cache](../data_source/data_cache.md)。该特性从 2.5 版本开始支持。