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add some tiflash tune instructions #6041

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Apr 16, 2021
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add some tiflash tune instructions #6041

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bfe7063
add some tiflash tune instructions
hanfei1991 Apr 15, 2021
d89efe2
Update tiflash/tune-tiflash-performance.md
hanfei1991 Apr 16, 2021
d7cf18c
Update tiflash/tune-tiflash-performance.md
hanfei1991 Apr 16, 2021
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10 changes: 10 additions & 0 deletions tiflash/tune-tiflash-performance.md
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Expand Up @@ -50,3 +50,13 @@ aliases: ['/docs-cn/dev/tiflash/tune-tiflash-performance/','/docs-cn/dev/referen
```sql
set @@tidb_opt_distinct_agg_push_down = 1;
```

5. 在 Join 没有选择 MPP 执行模式的情况下，调整参数使 Join 算子选择 MPP 执行：

`tidb_opt_network_factor` 变量用来设置优化器计算代价时考虑网络开销代价的比例。当这个值越小时，TiDB 对于大量网络传输的代价估算就更小，从而更倾向于选择 MPP 算子。

{{< copyable "sql" >}}

```sql
set @@tidb_opt_network_factor = 0.001;
```