乐趣区

关于索引:新特性解读-高效获取不连续主键区间

引言

明天碰到一个需要:客户有张表,主键自增。因为种种原因,主键值并非间断,两头有空隙。为了使主键间断,反复利用这些空隙,目前是用 MySQL 的非凡语法:INSERT IGNORE。

这种办法非常简单,不过会带来额定的失败重试。比方我上面往表 ytt_t0 插入一条存在的记录,前期须要不停的重试能力保障插入实现。

mysql> insert ignore ytt_t0 (id) values (1);
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+----------------------------------------------+
| Level   | Code | Message                                      |
+---------+------+----------------------------------------------+
| Warning | 1062 | Duplicate entry '1' for key 'ytt_t0.PRIMARY' |
+---------+------+----------------------------------------------+
1 row in set (0.00 sec)

客户纠结的问题是:那有没有一种从数据库角度来讲疾速找出这些不间断主键值的办法呢?

一、shell 端的实现办法

必定是有,不过我自己还是感觉这一块放在非数据库端会比拟好。比方思考在 Shell 端来实现这种需要,非常简单,效率又十分高。举个例子:

ytt_t0 蕴含以下数据:

最大值为 28,须要返回的后果为:5,6,7,8,9,10,11,16,17,18,20,21,22,23,24,25,26

mysql> select id from ytt_t0;
+----+
| id |
+----+
|  1 |
|  2 |
|  3 |
|  4 |
| 12 |
| 13 |
| 14 |
| 15 |
| 19 |
| 27 |
| 28 |
+----+
11 rows in set (0.00 sec

在 Shell 端用几条常用命令就可拿到这些空缺 ID 串:

root@debian-ytt1:/var/lib/mysql# mysql -S /tmp/mysqld_3306.sock -D ytt_big -e "select id from ytt_t0" -ss >ytt_t0_ids.txt

root@debian-ytt1:/var/lib/mysql# for i in `seq 1 28`;do echo $i >> ids.txt;done;

root@debian-ytt1:/var/lib/mysql# grep -vwf ytt_t0_ids.txt  ids.txt |sed ':label;N;s/\n/,/;b label'
5,6,7,8,9,10,11,16,17,18,20,21,22,23,24,25,26

即便须要找的 ID 区间十分大,Shell 端效率也很不错。比方:把 ID 最大设置为 10W,看下执行工夫。

数据端克隆张新表 ytt_t1,更新最大 ID 为 10W。

mysql> insert into ytt_t1 select * from ytt_t0;
Query OK, 11 rows affected (0.01 sec)
Records: 11  Duplicates: 0  Warnings: 0

mysql> update ytt_t1 set id = 100000 where id = 28;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

此时 Shell 端实现同样的需要:(大略 3 秒钟的样子,生成间断 ID 文件的过程最花工夫)

root@debian-ytt1:/var/lib/mysql# time for i in `seq 1 100000`;do echo $i >> ids_100000.txt;done;

real    0m2.796s
user    0m1.685s
sys     0m1.090s

root@debian-ytt1:/var/lib/mysql#  time mysql -S /tmp/mysqld_3306.sock -D ytt_big -e "select id from ytt_t1" -ss >ytt_t1_ids.txt

real    0m0.026s
user    0m0.010s
sys     0m0.015s

root@debian-ytt1:/var/lib/mysql# time grep -vwf ytt_t1_ids.txt  ids_100000.txt >ytt_t1_ids_diff.txt        
real    0m0.009s
user    0m0.009s
sys     0m0.000s

那么从数据库角度来讲,有没有还不错的办法呢?当然也是有的,接下来一一列举进去。

二、数据库端的实现办法

1、生成一个残缺序列表,和原始表做 JOIN,就能拿出有空隙的主键值,适宜所有 MySQL 版本。

这块儿工夫开销有两个中央:一个是残缺序列表生成的工夫;另外一个是两表 JOIN 的工夫。

序列表的生成:

mysql> create table ytt_seq(id serial primary key);
Query OK, 0 rows affected (0.04 sec)

写个简略存储过程来生成序列表数据:

DELIMITER $$

USE `ytt_big`$$

DROP PROCEDURE IF EXISTS `sp_generate_series`$$

CREATE DEFINER=`root`@`%` PROCEDURE `sp_generate_series`(f_tbname VARCHAR(64),
    f_max_id BIGINT UNSIGNED
    )
BEGIN
 DECLARE i BIGINT DEFAULT 0;
 TRUNCATE ytt_seq;
 SET @@autocommit = 0;
 WHILE i < f_max_id DO
   SET @stmt = CONCAT("insert into",f_tbname,"select null");
   PREPARE s1 FROM @stmt;
   EXECUTE s1;
   IF MOD(i,100) = 0 THEN
     COMMIT;
   END IF;
   SET i = i + 1;
 END WHILE;
 drop prepare s1;
 COMMIT;
 SET @@autocommit = 1;
 END$$

DELIMITER ;

依据原始表最大值生成序列表数据:

mysql> select max(id) from ytt_t0 into @max_id;
Query OK, 1 row affected (0.00 sec)

mysql> call sp_generate_series('ytt_seq',@max_id);
Query OK, 0 rows affected (0.09 sec)

两表 JOIN 失去须要的后果:

mysql> SELECT
    ->   GROUP_CONCAT(ytt_seq.id) AS result
    -> FROM
    ->   ytt_t0
    ->   RIGHT JOIN ytt_seq USING (id)
    -> WHERE ytt_t0.id IS NULL;
+-----------------------------------------------+
| result                                        |
+-----------------------------------------------+
| 5,6,7,8,9,10,11,16,17,18,20,21,22,23,24,25,26 |
+-----------------------------------------------+
1 row in set (0.00 sec)

减少最大值,针对表 ytt_t1 来看:

mysql>  select max(id) from ytt_t1 into @max_id;
Query OK, 1 row affected (0.01 sec)

mysql> call sp_generate_series('ytt_seq',@max_id);
Query OK, 0 rows affected (21.80 sec)

mysql>  SELECT
    ->   ytt_seq.id AS result
    ->  FROM
    ->    ytt_t1
    ->    RIGHT JOIN ytt_seq USING (id)
    ->  WHERE ytt_t1.id IS NULL;

99989 rows in set (0.25 sec)

从后果能够看到,生成这个 ID 序列表数据须要的工夫为 21.8 秒最长,两表 JOIN 工夫 0.25 秒,如果能提前生成这个序列表,这个工夫就很快了。

2、模仿内部程序,用零碎函数来解决,零碎函数如果不能满足需要,能够本人写函数来解决,效率最差,毕竟这个不是数据库善于的事件。(适宜所有 MySQL 版本,当然 MySQL 8.0 实现更加简略)

这里我利用 JSON_OVERLAPS 函数判断 JSON 数组是否反复,本人写了两个函数,一个是生成 JSON 序列,另外一个是对两个 JSON 数组进行比照,拿出不属于交加的后果,当然最耗时间的仍然还是生成 JSON 序列的函数:

先拿出老的 ID 序列:

mysql> select @arr1 from (select @arr1 := json_array_append(@arr1,'$',id) from ytt_t0,(select @arr1 := '[]') b) T limit 1;
+------------------------------------------+
| @arr1                                    |
+------------------------------------------+
| [1, 2, 3, 4, 12, 13, 14, 15, 19, 27, 28] |
+------------------------------------------+
1 row in set, 2 warnings (0.00 sec)

生成残缺的 JSON 序列:

DELIMITER $$

USE `ytt_big`$$

DROP FUNCTION IF EXISTS `func_generate_series_json`$$

CREATE DEFINER=`root`@`%` FUNCTION `func_generate_series_json`(f_max_id BIGINT UNSIGNED) RETURNS JSON
BEGIN
      DECLARE v_result JSON DEFAULT '[]';
      DECLARE i BIGINT UNSIGNED DEFAULT 1;
      WHILE i <= f_max_id DO
        SET v_result = JSON_ARRAY_APPEND(v_result,'$',i);
        SET i = i + 1;
      END WHILE;
      RETURN v_result;
    END$$

DELIMITER ;

再写一个 JSON 序列比照函数:

DELIMITER $$

USE `ytt_big`$$

DROP FUNCTION IF EXISTS `func_get_json_common_values`$$

CREATE DEFINER=`root`@`%` FUNCTION `func_get_json_common_values`(
    f_str JSON,
    f_sub_str JSON
    ) RETURNS JSON
BEGIN
      DECLARE i,v_len INT UNSIGNED DEFAULT 0;
      DECLARE v_tmp_str,v_result,v_str JSON DEFAULT '[]';
      SET v_str = f_str;
      SET v_len = JSON_LENGTH(v_str);

  WHILE i < v_len DO
    SET v_tmp_str = JSON_EXTRACT(v_str,'$[0]');
    IF json_overlaps(v_tmp_str,f_sub_str) = 0 THEN
      SET v_result = JSON_ARRAY_APPEND(v_result,'$',v_tmp_str);
    END IF;
    SET v_str = JSON_REMOVE(v_str,'$[0]');
    SET i = i + 1;
  END WHILE;
  RETURN v_result;
END$$

DELIMITER ;

接下来执行这两个函数失去后果:(数据十分小,工夫能够忽略不计)

mysql> select @arr1 from (select @arr1 := json_array_append(@arr1,'$',id) from ytt_t0,(select @arr1 := '[]') b) T limit 1;
+------------------------------------------+
| @arr1                                    |
+------------------------------------------+
| [1, 2, 3, 4, 12, 13, 14, 15, 19, 27, 28] |
+------------------------------------------+
1 row in set, 2 warnings (0.00 sec)


mysql> select max(id) from ytt_t0 into @max_id;
Query OK, 1 row affected (0.00 sec)

mysql> select func_get_json_common_values(func_generate_series_json(@max_id),@arr1) as result;
+-----------------------------------------------------------------+
| result                                                          |
+-----------------------------------------------------------------+
| [5, 6, 7, 8, 9, 10, 11, 16, 17, 18, 20, 21, 22, 23, 24, 25, 26] |
+-----------------------------------------------------------------+
1 row in set (0.00 sec)

再来从表 ytt_t1 里拿后果,我这儿省略两头过程,只看函数最终执行工夫:

mysql> select DB,COMMAND,TIME,INFO from information_schema.processlist where DB = 'ytt_big'\G
*************************** 1. row ***************************
     DB: ytt_big
COMMAND: Query
   TIME: 628
   INFO: select func_get_json_common_values(func_generate_series_json(@max_id),@arr1) as result
1 row in set (0.00 sec)

好吧,执行了 10 分钟,没进去后果,放弃了!

3、间接用通过表达式来解决(MySQL 8.0 特有,数据库自身的个性,在数据库层面来讲,效率必定最高)。实现非常简单,间接用 WITH 表达式生成序列,完了和原始表做 JOIN,一条 SQL 就失去后果:

mysql>  WITH recursive tmp (id) AS
    ->  (
    ->  SELECT  1 FROM DUAL
    ->  UNION ALL
    ->  SELECT  id + 1 FROM  tmp
    ->  WHERE id < (SELECT MAX(id) FROM ytt_t0)
    ->  )
    ->  SELECT
    ->    id  AS gap_result
    ->  FROM  tmp
    ->  LEFT JOIN ytt_t0 USING (id)
    ->  WHERE ytt_t0.id IS NULL;
+------------+
| gap_result |
+------------+
|          5 |
|          6 |
|          7 |
|          8 |
|          9 |
|         10 |
|         11 |
|         16 |
|         17 |
|         18 |
|         20 |
|         21 |
|         22 |
|         23 |
|         24 |
|         25 |
|         26 |
+------------+
17 rows in set (0.00 sec)

持续看下针对表 ytt_t1:(只花了 0.19 秒)

mysql> set cte_max_recursion_depth=1000000;
Query OK, 0 rows affected (0.01 sec)

mysql>  WITH recursive tmp (id) AS
    ->  (
    ->  SELECT  1 FROM DUAL
    ->  UNION ALL
    ->  SELECT  id + 1 FROM  tmp
    ->  WHERE id < (SELECT MAX(id) FROM ytt_t1)
    ->  )
    ->  SELECT
    ->    id  AS gap_result
    ->  FROM  tmp
    ->  LEFT JOIN ytt_t1 USING (id)
    ->  WHERE ytt_t1.id IS NULL;

...

99989 rows in set (0.19 sec)

其实后果不言而喻,如果非要在数据库端实现这样的需要,MySQL 8.0 是最好的抉择;要不然,放到内部程序是最好的抉择。

退出移动版