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add docs for mpp partition table support #8698

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Mar 28, 2022
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add docs for mpp partition table support #8698

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add docs about mpp partition table support
windtalker Mar 16, 2022
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fix
windtalker Mar 16, 2022
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add more
windtalker Mar 25, 2022
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Adjust wording and fix jenkins
shichun-0415 Mar 28, 2022
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Update tiflash/use-tiflash.md
windtalker Mar 28, 2022
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shichun-0415 Mar 28, 2022
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shichun-0415 Mar 28, 2022
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91 changes: 78 additions & 13 deletions tiflash/use-tiflash.md
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Original file line number Diff line number Diff line change
Expand Up @@ -118,34 +118,34 @@ SELECT * FROM information_schema.tiflash_replica WHERE TABLE_SCHEMA = '<db_name>

```shell
> tiup ctl:<version> pd -u<pd-host>:<pd-port> store

...

"address": "172.16.5.82:23913",
"labels": [
{ "key": "engine", "value": "tiflash"},
{ "key": "zone", "value": "z1" }
],
"region_count": 4,

...

"address": "172.16.5.81:23913",
"labels": [
{ "key": "engine", "value": "tiflash"},
{ "key": "zone", "value": "z1" }
],
"region_count": 5,

...

"address": "172.16.5.85:23913",
"labels": [
{ "key": "engine", "value": "tiflash"},
{ "key": "zone", "value": "z2" }
],
"region_count": 9,

...
```

Expand Down Expand Up @@ -432,6 +432,71 @@ TiFlash 提供了两个全局/会话变量决定是否选择 Broadcast Hash Join
- [`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。

### MPP 模式访问分区表

当 TiDB 以 [`dynamic` 模式](/partitioned-table.md#动态裁剪模式)访问分区表且查询涉及分区表时，该查询可以使用 MPP 模式。
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> **注意：**
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>
> 目前，分区表的 `dynamic` 分区裁剪模式为实验特性，不建议在生产环境中使用。
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示例如下：

```sql
mysql> DROP TABLE if exists test.employees;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> CREATE TABLE test.employees ( id int(11) NOT NULL, fname varchar(30) DEFAULT NULL, lname varchar(30) DEFAULT NULL, hired date NOT NULL DEFAULT '1970-01-01', separated date DEFAULT '99
99-12-31', job_code int(11) DEFAULT NULL, store_id int(11) NOT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin PARTITION BY RANGE (store_id) (PARTITION p0 VALUES LESS THAN (
6), PARTITION p1 VALUES LESS THAN (11), PARTITION p2 VALUES LESS THAN (16), PARTITION p3 VALUES LESS THAN (MAXVALUE));
Query OK, 0 rows affected (0.10 sec)

mysql> ALTER table test.employees SET tiflash replica 1;
Query OK, 0 rows affected (0.09 sec)

mysql> SET tidb_partition_prune_mode=static;
Query OK, 0 rows affected (0.00 sec)

mysql> explain SELECT count(*) FROM test.employees;
+----------------------------------+----------+-------------------+-------------------------------+-----------------------------------+
| id | estRows | task | access object | operator info |
+----------------------------------+----------+-------------------+-------------------------------+-----------------------------------+
| HashAgg_19 | 1.00 | root | | funcs:count(Column#10)->Column#9 |
| └─PartitionUnion_21 | 4.00 | root | | |
| ├─StreamAgg_40 | 1.00 | root | | funcs:count(Column#12)->Column#10 |
| │ └─TableReader_41 | 1.00 | root | | data:StreamAgg_27 |
| │ └─StreamAgg_27 | 1.00 | batchCop[tiflash] | | funcs:count(1)->Column#12 |
| │ └─TableFullScan_39 | 10000.00 | batchCop[tiflash] | table:employees, partition:p0 | keep order:false, stats:pseudo |
| ├─StreamAgg_63 | 1.00 | root | | funcs:count(Column#14)->Column#10 |
| │ └─TableReader_64 | 1.00 | root | | data:StreamAgg_50 |
| │ └─StreamAgg_50 | 1.00 | batchCop[tiflash] | | funcs:count(1)->Column#14 |
| │ └─TableFullScan_62 | 10000.00 | batchCop[tiflash] | table:employees, partition:p1 | keep order:false, stats:pseudo |
| ├─StreamAgg_86 | 1.00 | root | | funcs:count(Column#16)->Column#10 |
| │ └─TableReader_87 | 1.00 | root | | data:StreamAgg_73 |
| │ └─StreamAgg_73 | 1.00 | batchCop[tiflash] | | funcs:count(1)->Column#16 |
| │ └─TableFullScan_85 | 10000.00 | batchCop[tiflash] | table:employees, partition:p2 | keep order:false, stats:pseudo |
| └─StreamAgg_109 | 1.00 | root | | funcs:count(Column#18)->Column#10 |
| └─TableReader_110 | 1.00 | root | | data:StreamAgg_96 |
| └─StreamAgg_96 | 1.00 | batchCop[tiflash] | | funcs:count(1)->Column#18 |
| └─TableFullScan_108 | 10000.00 | batchCop[tiflash] | table:employees, partition:p3 | keep order:false, stats:pseudo |
+----------------------------------+----------+-------------------+-------------------------------+-----------------------------------+
18 rows in set, 4 warnings (0.00 sec)

mysql> SET tidb_partition_prune_mode=dynamic;
Query OK, 0 rows affected (0.00 sec)

mysql> explain SELECT count(*) FROM test.employees;
+------------------------------+----------+-------------------+-----------------+----------------------------------+
| id | estRows | task | access object | operator info |
+------------------------------+----------+-------------------+-----------------+----------------------------------+
| HashAgg_21 | 1.00 | root | | funcs:count(Column#11)->Column#9 |
| └─TableReader_23 | 1.00 | root | partition:all | data:ExchangeSender_22 |
| └─ExchangeSender_22 | 1.00 | batchCop[tiflash] | | ExchangeType: PassThrough |
| └─HashAgg_9 | 1.00 | batchCop[tiflash] | | funcs:count(1)->Column#11 |
| └─TableFullScan_20 | 10000.00 | batchCop[tiflash] | table:employees | keep order:false, stats:pseudo |
+------------------------------+----------+-------------------+-----------------+----------------------------------+
```

## TiFlash 数据校验

### 使用场景
Expand Down Expand Up @@ -483,27 +548,27 @@ TiFlash 在以下情况与 TiDB 存在不兼容问题：
```sql
mysql> create table t (a decimal(3,0), b decimal(10, 0));
Query OK, 0 rows affected (0.07 sec)

mysql> insert into t values (43, 1044774912);
Query OK, 1 row affected (0.03 sec)

mysql> alter table t set tiflash replica 1;
Query OK, 0 rows affected (0.07 sec)

mysql> set session tidb_isolation_read_engines='tikv';
Query OK, 0 rows affected (0.00 sec)

mysql> select a/b, a/b + 0.0000000000001 from t where a/b;
+--------+-----------------------+
| a/b | a/b + 0.0000000000001 |
+--------+-----------------------+
| 0.0000 | 0.0000000410001 |
+--------+-----------------------+
1 row in set (0.00 sec)

mysql> set session tidb_isolation_read_engines='tiflash';
Query OK, 0 rows affected (0.00 sec)

mysql> select a/b, a/b + 0.0000000000001 from t where a/b;
Empty set (0.01 sec)
```
Expand Down