yangzhg d3d835844f [Performance] Improve performance of unique table read (#3974) ...

Implements #3971 
the test table as list:
```
mysql> desc test;
+------------+---------+------+-------+---------+---------+
| Field      | Type    | Null | Key   | Default | Extra   |
+------------+---------+------+-------+---------+---------+
| rid        | BIGINT  | No   | true  | 0       |         |
| qid        | BIGINT  | No   | true  | 0       |         |
| qidDeleted | TINYINT | No   | false | 0       | REPLACE |
| type       | TINYINT | No   | false | 0       | REPLACE |
| uid        | BIGINT  | No   | false | 0       | REPLACE |
| toUid      | BIGINT  | No   | false | 0       | REPLACE |
| status     | INT     | No   | false | 0       | REPLACE |
| createTime | INT     | No   | false | 0       | REPLACE |
| source     | INT     | No   | false | 0       | REPLACE |
| misFlag    | INT     | No   | false | 0       | REPLACE |
| anonymous  | TINYINT | No   | false | 0       | REPLACE |
| uv         | TINYINT | No   | false | 1       | REPLACE |
+------------+---------+------+-------+---------+---------+
12 rows in set (0.00 sec)

mysql> select count(*) from test;
+----------+
| count(*) |
+----------+
|  1093760 |
+----------+
1 row in set (1.00 sec)
```
There is 29 versions at present
![image](https://user-images.githubusercontent.com/9098473/85992244-2aa26c80-ba27-11ea-918a-04701a58dbdf.png)
I run the query `select sum(uv) from test` for 10 times,
the average ScanTime reduced from `9s277ms`  to `8s206ms`

2020-07-02 13:56:08 +08:00

..

src

[Performance] Improve performance of unique table read (#3974)

2020-07-02 13:56:08 +08:00

test

[Bug] Fix bug that routine load task throw exception when calling afterVisible() (#3979)

2020-07-01 09:22:33 +08:00

CMakeLists.txt

[UDF] Support external users to contribute udf (#3760)

2020-06-23 13:43:08 +08:00