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Reverted: update bcj threshold #6875

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Aug 17, 2021
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Reverted: update bcj threshold #6875

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ffd4793
update bcj threshold
hanfei1991 Aug 16, 2021
d95b814
update bcj threshold
hanfei1991 Aug 16, 2021
614d52e
Update system-variables.md
LittleFall Aug 16, 2021
58d7685
Update use-tiflash.md
LittleFall Aug 16, 2021
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hanfei1991 Aug 17, 2021
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8 changes: 4 additions & 4 deletions system-variables.md
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Expand Up @@ -328,16 +328,16 @@ MPP 是 TiFlash 引擎提供的分布式计算框架，允许节点之间的数

- 作用域：SESSION | GLOBAL
- 默认值：`10240`
- 范围：`[0, 9223372036854775807]`
- 单位为行数。如果 join 的对象为子查询，优化器无法估计子查询结果集大小，在这种情况下通过结果集行数判断。如果子查询的行数估计值小于该变量，则选择 Broadcast Hash Join 算法。否则选择 Shuffled Hash Join 算法。
- 范围：`[-1, 9223372036854775807]`
- 单位为行数。如果 join 的对象为子查询，优化器无法估计子查询结果集大小，在这种情况下通过结果集行数判断。如果子查询的行数估计值小于该变量，则选择 Broadcast Hash Join 算法。否则选择 Shuffled Hash Join 算法。当设置为 -1 时，该阈值无穷大。

### `tidb_broadcast_join_threshold_size` <span class="version-mark">从 v5.0 版本开始引入</span>

- 作用域：SESSION | GLOBAL
- 默认值：`104857600` (100 MiB)
- 范围：`[0, 9223372036854775807]`
- 范围：`[-1, 9223372036854775807]`
- 单位：字节
- 如果表大小（字节数）小于该值，则选择 Broadcast Hash Join 算法。否则选择 Shuffled Hash Join 算法。
- 如果表大小（字节数）小于该值，则选择 Broadcast Hash Join 算法。否则选择 Shuffled Hash Join 算法。当设置为 -1 时，该阈值无穷大。

### `tidb_build_stats_concurrency`

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4 changes: 2 additions & 2 deletions tiflash/use-tiflash.md
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Expand Up @@ -347,8 +347,8 @@ mysql> explain select count(*) from customer c join nation n on c.c_nationkey=n.

TiFlash 提供了两个全局/会话变量决定是否选择 Broadcast Hash Join，分别为：

- [`tidb_broadcast_join_threshold_size`](/system-variables.md#tidb_broadcast_join_threshold_count-从-v50-版本开始引入)，单位为 bytes。如果表大小（字节数）小于该值，则选择 Broadcast Hash Join 算法。否则选择 Shuffled Hash Join 算法。
- [`tidb_broadcast_join_threshold_count`](/system-variables.md#tidb_broadcast_join_threshold_count-从-v50-版本开始引入)，单位为行数。如果 join 的对象为子查询，优化器无法估计子查询结果集大小，在这种情况下通过结果集行数判断。如果子查询的行数估计值小于该变量，则选择 Broadcast Hash Join 算法。否则选择 Shuffled Hash Join 算法。
- [`tidb_broadcast_join_threshold_size`](/system-variables.md#tidb_broadcast_join_threshold_count-从-v50-版本开始引入)，单位为 bytes。如果表大小（字节数）小于该值，则选择 Broadcast Hash Join 算法。否则选择 Shuffled Hash Join 算法。当设置为 -1 时，该阈值无穷大。
- [`tidb_broadcast_join_threshold_count`](/system-variables.md#tidb_broadcast_join_threshold_count-从-v50-版本开始引入)，单位为行数。如果 join 的对象为子查询，优化器无法估计子查询结果集大小，在这种情况下通过结果集行数判断。如果子查询的行数估计值小于该变量，则选择 Broadcast Hash Join 算法。否则选择 Shuffled Hash Join 算法。当设置为 -1 时，该阈值无穷大。

## 注意事项

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