千萬級別mysql合並表快速去重簡析
mysql合並表去重
目標：
現有表a和b，把兩個表中的數據合並去重到c表中。其中a和b表中數據量大概在2千萬左右。
基本情況
操作系統版本：CentOS release 5.6 64位
操作系統內存：8G
數據庫版本：5.1.56-community 64位
數據庫初始化參數：默認
數據庫表和數據量
表a： www.2cto.com
mysql> desc a2kw;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| c1 | varchar(20) | YES | MUL | NULL | |
| c2 | varchar(30) | YES | | NULL | |
| c3 | varchar(12) | YES | | NULL | |
| c4 | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
表b
mysql> desc b2kw;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| c1 | varchar(20) | YES | | NULL | |
| c2 | varchar(30) | YES | | NULL | |
| c3 | varchar(12) | YES | | NULL | |
| c4 | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
a和b表的數據概況如下
mysql> select * from a2kw limit 10;
+-----------+-----------+------+----------+
| c1 | c2 | c3 | c4 |
+-----------+-----------+------+----------+
| 662164461 | 131545534 | TOM0 | 20120520 |
| 226662142 | 605685564 | TOM0 | 20120516 |
| 527008225 | 172557633 | TOM0 | 20120514 |
| 574408183 | 350897450 | TOM0 | 20120510 |
| 781619324 | 583989494 | TOM0 | 20120510 |
| 158872754 | 775676430 | TOM0 | 20120512 |
| 815875622 | 631631832 | TOM0 | 20120514 |
| 905943640 | 477433083 | TOM0 | 20120514 |
| 660790641 | 616774715 | TOM0 | 20120512 |
| 999083595 | 953186525 | TOM0 | 20120513 |
+-----------+-----------+------+----------+
10 rows in set (0.01 sec)
基本步驟 www.2cto.com
1、在B表上創建索引
mysql> select count(*) from b2kw;
+----------+
| count(*) |
+----------+
| 20000002 |
+----------+
1 row in set (0.00 sec)
mysql> create index ind_b2kw_c1 on b2kw(c1);
Query OK, 20000002 rows affected (1 min 2.94 sec)
Records: 20000002 Duplicates: 0 Warnings: 0
數據量為：20000002 ,時間為：1 min 2.94 sec
2、把a、b分別插入中間表temp表中
創建中間表
mysql> create table temp select * from c2kw where 1=2;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
插入數據
mysql> insert into temp select * from a2kw;
Query OK, 20000002 rows affected (13.23 sec)
Records: 20000002 Duplicates: 0 Warnings: 0
mysql> insert into temp select * from b2kw;
Query OK, 20000002 rows affected (13.27 sec)
Records: 20000002 Duplicates: 0 Warnings: 0
www.2cto.com
mysql> select count(*) from temp;
+----------+
| count(*) |
+----------+
| 40000004 |
+----------+
1 row in set (0.00 sec)
數據量為：40000004 ,時間為：26.50 sec
3、temp建立聯合索引，強制索引去掉重復數據
mysql> create index ind_temp_c123 on temp(c1,c2,c3);
Query OK, 40000004 rows affected (3 min 43.87 sec)
Records: 40000004 Duplicates: 0 Warnings: 0
查看執行計劃
mysql> explain select c1,c2,c3,max(c4) from temp FORCE INDEX
(ind_temp_c123) group by c1,c2,c3 ;
+----+-------------+-------+-------+---------------+----------
-----+---------+------+----------+-------+
| id | select_type | table | type | possible_keys | key
| key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+-------------
--+---------+------+----------+-------+
| 1 | SIMPLE | temp | index | NULL | ind_temp_c123 | 71
| NULL | 40000004 | |
+----+-------------+-------+ www.2cto.com -------+---------------+--------
-------+---------+------+----------+-------+
1 row in set (0.05 sec)
mysql> insert into c2kw select c1,c2,c3,max(c4) from temp
FORCE INDEX (ind_temp_c123) group by c1,c2,c3 ;
Query OK, 20000004 rows affected (2 min 0.85 sec)
Records: 20000004 Duplicates: 0 Warnings: 0
實際大約花費實際為：6 min
4、刪除中間表
mysql> drop table temp;
Query OK, 0 rows affected (0.99 sec)
實際大約花費實際為：1 sec
5、建立c索引
mysql> create index ind_c2kw_c1 on c2kw(c1);
Query OK, 20000004 rows affected (49.74 sec)
Records: 20000004 Duplicates: 0 Warnings: 0
mysql> create index ind_c2kw_c2 on c2kw(c2);
Query OK, 20000004 rows affected (1 min 47.20 sec)
Records: 20000004 Duplicates: 0 Warnings: 0
mysql> create index ind_c2kw_c3 on c2kw(c3);
Query OK, 20000004 rows affected (2 min 42.02 sec)
Records: 20000004 Duplicates: 0 Warnings: 0
實際大約花費實際為：5分鐘 www.2cto.com
6、清空a、b表
mysql> truncate table a2kw;
Query OK, 0 rows affected (1.15 sec)
mysql> truncate table b2kw;
Query OK, 0 rows affected (1.34 sec)
實際大約花費實際為：3sec
一共花費的時間大概在15分鐘左右
作者 RuleV5
