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Aug 18, 2025
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docs: minor #249

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10 changes: 6 additions & 4 deletions zh_CN/development-guide/high-performance-reading.md
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Expand Up @@ -53,12 +53,14 @@ path = "/var/lib/datalayers/cache/file"

SQL Hints 是一种在 SQL 查询中嵌入的特殊指令，用于指导数据库优化器选择特定的执行计划，从而提升查询性能或解决优化器的决策偏差。Datalayers 在 v2.3.9 开始支持该特性。

### 语法

```sql
SELECT /*+ SET_VAR(parallel_degree=1) */ * FROM table;
```

### 查询并行度控制

在查询时，Datalayers 默认策略会尝试调度更多的 CPU 资源，通过并行化将任务拆分为多个子任务（如数据分片、并行扫描、聚合）来加速查询。这种逻辑对于数据量较大时有显著优势，但对于小查询则会带来一定的副作用。因此在小查询时通过指定并行度，可极大提升查询 QPS 与性能。在时序场景，一般来说查询某设备一小段时间范围内的数据，建议设置 `parallel_degree=1`，可显著提升系统查询的 QPS。

#### 语法

```sql
SELECT /*+ SET_VAR(parallel_degree=1) */ * FROM table;
```
2 changes: 1 addition & 1 deletion zh_CN/releases/changes.md
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Expand Up @@ -7,7 +7,7 @@
### 新功能
- **​SQL HINTS**
- 新增对SQL Hints的支持，允许开发者在查询中嵌入优化器指令，以干预执行计划生成。
- ​**​并行查询​​：**通过 parallel_degree 控制查询并行度（如：/*+ SET_VAR(parallel_degree=1) */）
- ​**​并行查询​**​：通过 parallel_degree 控制查询并行度（如：/*+ SET_VAR(parallel_degree=1) */）

### 增强
- **优化查询逻辑​​**
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