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Update use-tiflash.md
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LittleFall authored Aug 16, 2021
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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。当值为 -1 时,默认选择 broadcast_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。当值为 -1 时,默认选择 broadcast_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,代表无穷大
- [`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,代表无穷大
## 注意事项
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