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Reverted: System variables: update broadcast_join_threshold_count and `broadc… #6181

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Reverted: System variables: update broadcast_join_threshold_count and `broadc… #6181

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System variables: update `broadcast_join_threshold_count` and `broadc…
en-jin19 Aug 17, 2021
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8 changes: 4 additions & 4 deletions system-variables.md
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Expand Up @@ -321,16 +321,16 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a

- Scope: SESSION | GLOBAL
- Default value: `10240`
- Range: `[0, 9223372036854775807]`
- The unit of the variable is rows. If the objects of the join operation belong to a subquery, the optimizer cannot estimate the size of the subquery result set. In this situation, the size is determined by the number of rows in the result set. If the estimated number of rows in the subquery is less than the value of this variable, the Broadcast Hash Join algorithm is used. Otherwise, the Shuffled Hash Join algorithm is used.
- Range: `[-1, 9223372036854775807]`
- The unit of the variable is rows. If the objects of the join operation belong to a subquery, the optimizer cannot estimate the size of the subquery result set. In this situation, the size is determined by the number of rows in the result set. If the estimated number of rows in the subquery is less than the value of this variable, the Broadcast Hash Join algorithm is used. Otherwise, the Shuffled Hash Join algorithm is used. When `tidb_broadcast_join_threshold_count = -1`, the threshold is infinitely high.

### tidb_broadcast_join_threshold_size <span class="version-mark">New in v5.0</span>

- Scope: SESSION | GLOBAL
- Default value: `104857600` (100 MiB)
- Range: `[0, 9223372036854775807]`
- Range: `[-1, 9223372036854775807]`
- Unit: Bytes
- If the table size is less than the value of the variable, the Broadcast Hash Join algorithm is used. Otherwise, the Shuffled Hash Join algorithm is used.
- If the table size is less than the value of the variable, the Broadcast Hash Join algorithm is used. Otherwise, the Shuffled Hash Join algorithm is used. When `tidb_broadcast_join_threshold_size = -1`, the threshold is infinitely high.

### tidb_build_stats_concurrency

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4 changes: 2 additions & 2 deletions tiflash/use-tiflash.md
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Expand Up @@ -353,8 +353,8 @@ In the example execution plan, the `ExchangeReceiver` and `ExchangeSender` opera

TiFlash provides the following two global/session variables to control whether to use Broadcast Hash Join:

- [`tidb_broadcast_join_threshold_size`](/system-variables.md#tidb_broadcast_join_threshold_count-new-in-v50): The unit of the value is bytes. If the table size (in the unit of bytes) is less than the value of the variable, the Broadcast Hash Join algorithm is used. Otherwise, the Shuffled Hash Join algorithm is used.
- [`tidb_broadcast_join_threshold_count`](/system-variables.md#tidb_broadcast_join_threshold_count-new-in-v50): The unit of the value is rows. If the objects of the join operation belong to a subquery, the optimizer cannot estimate the size of the subquery result set, so the size is determined by the number of rows in the result set. If the estimated number of rows in the subquery is less than the value of this variable, the Broadcast Hash Join algorithm is used. Otherwise, the Shuffled Hash Join algorithm is used.
- [`tidb_broadcast_join_threshold_size`](/system-variables.md#tidb_broadcast_join_threshold_count-new-in-v50): The unit of the value is bytes. If the table size (in the unit of bytes) is less than the value of the variable, the Broadcast Hash Join algorithm is used. Otherwise, the Shuffled Hash Join algorithm is used. When `tidb_broadcast_join_threshold_size = -1`, the threshold is infinitely high.
- [`tidb_broadcast_join_threshold_count`](/system-variables.md#tidb_broadcast_join_threshold_count-new-in-v50): The unit of the value is rows. If the objects of the join operation belong to a subquery, the optimizer cannot estimate the size of the subquery result set, so the size is determined by the number of rows in the result set. If the estimated number of rows in the subquery is less than the value of this variable, the Broadcast Hash Join algorithm is used. Otherwise, the Shuffled Hash Join algorithm is used. When `tidb_broadcast_join_threshold_count = -1`, the threshold is infinitely high.

## Notes

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