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item_id int, created_time datetime, modified_time datetime, item_name varchar(20), other varchar(20)
要求:
1.源表中有100万条数据,其中有50万created_time和item_name重复。
2.要把去重后的50万数据写入到目标表。
3.重复created_time和item_name的多条数据,可以保留任意一条,不做规则限制。
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-- 建立源表 create table t_source ( item_id int, created_time datetime, modified_time datetime, item_name varchar(20), other varchar(20) ); -- 建立目标表 create table t_target like t_source; -- 生成100万测试数据,其中有50万created_time和item_name重复 delimiter // create procedure sp_generate_data() begin set @i := 1; while @i<=500000 do set @created_time := date_add('2017-01-01',interval @i second); set @modified_time := @created_time; set @item_name := concat('a',@i); insert into t_source values (@i,@created_time,@modified_time,@item_name,'other'); set @i:=@i+1; end while; commit; set @last_insert_id := 500000; insert into t_source select item_id + @last_insert_id, created_time, date_add(modified_time,interval @last_insert_id second), item_name, 'other' from t_source; commit; end // delimiter ; call sp_generate_data(); -- 源表没有主键或唯一性约束,有可能存在两条完全一样的数据,所以再插入一条记录模拟这种情况。 insert into t_source select * from t_source where item_id=1; 源表中有1000001条记录,去重后的目标表应该有500000条记录。 mysql> select count(*),count(distinct created_time,item_name) from t_source; +----------+----------------------------------------+ | count(*) | count(distinct created_time,item_name) | +----------+----------------------------------------+ | 1000001 | 500000 | +----------+----------------------------------------+ 1 row in set (1.92 sec)
一、巧用索引与变量
1. 无索引对比测试
(1)使用相关子查询
truncate t_target; insert into t_target select distinct t1.* from t_source t1 where item_id in (select min(item_id) from t_source t2 where t1.created_time=t2.created_time and t1.item_name=t2.item_name);
这个语句很长时间都出不来结果,只看一下执行计划吧。
mysql> explain select distinct t1.* from t_source t1 where item_id in -> (select min(item_id) from t_source t2 where t1.created_time=t2.created_time and t1.item_name=t2.item_name); +----+--------------------+-------+------------+------+---------------+------+---------+------+--------+----------+------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+--------------------+-------+------------+------+---------------+------+---------+------+--------+----------+------------------------------+ | 1 | PRIMARY | t1 | NULL | ALL | NULL | NULL | NULL | NULL | 997282 | 100.00 | Using where; Using temporary | | 2 | DEPENDENT SUBQUERY | t2 | NULL | ALL | NULL | NULL | NULL | NULL | 997282 | 1.00 | Using where | +----+--------------------+-------+------------+------+---------------+------+---------+------+--------+----------+------------------------------+ 2 rows in set, 3 warnings (0.00 sec)
主查询和相关子查询都是全表扫描,一共要扫描100万*100万数据行,难怪出不来结果。
(2)使用表连接
truncate t_target; insert into t_target select distinct t1.* from t_source t1, (select min(item_id) item_id,created_time,item_name from t_source group by created_time,item_name) t2 where t1.item_id = t2.item_id;
这种方法用时14秒,查询计划如下:
mysql> explain select distinct t1.* from t_source t1, (select min(item_id) item_id,created_time,item_name from t_source group by created_time,item_name) t2 where t1.item_id = t2.item_id; +----+-------------+------------+------------+------+---------------+-------------+---------+-----------------+--------+----------+------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+------------+------------+------+---------------+-------------+---------+-----------------+--------+----------+------------------------------+ | 1 | PRIMARY | t1 | NULL | ALL | NULL | NULL | NULL | NULL | 997282 | 100.00 | Using where; Using temporary | | 1 | PRIMARY | <derived2> | NULL | ref | <auto_key0> | <auto_key0> | 5 | test.t1.item_id | 10 | 100.00 | Distinct | | 2 | DERIVED | t_source | NULL | ALL | NULL | NULL | NULL | NULL | 997282 | 100.00 | Using temporary | +----+-------------+------------+------------+------+---------------+-------------+---------+-----------------+--------+----------+------------------------------+ 3 rows in set, 1 warning (0.00 sec)
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set @a:='1000-01-01 00:00:00'; set @b:=' '; set @f:=0; truncate t_target; insert into t_target select item_id,created_time,modified_time,item_name,other from (select t0.*,if(@a=created_time and @b=item_name,@f:=0,@f:=1) f, @a:=created_time,@b:=item_name from (select * from t_source order by created_time,item_name) t0) t1 where f=1;
这种方法用时13秒,查询计划如下:
mysql> explain select item_id,created_time,modified_time,item_name,other -> from -> (select t0.*,if(@a=created_time and @b=item_name,@f:=0,@f:=1) f, @a:=created_time,@b:=item_name -> from -> (select * from t_source order by created_time,item_name) t0) t1 where f=1; +----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+----------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+----------------+ | 1 | PRIMARY | <derived2> | NULL | ref | <auto_key0> | <auto_key0> | 4 | const | 10 | 100.00 | NULL | | 2 | DERIVED | <derived3> | NULL | ALL | NULL | NULL | NULL | NULL | 997282 | 100.00 | NULL | | 3 | DERIVED | t_source | NULL | ALL | NULL | NULL | NULL | NULL | 997282 | 100.00 | Using filesort | +----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+----------------+ 3 rows in set, 5 warnings (0.00 sec)
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-- 建立created_time和item_name字段的联合索引 create index idx_sort on t_source(created_time,item_name,item_id); analyze table t_source;
(1)使用相关子查询
truncate t_target; insert into t_target select distinct t1.* from t_source t1 where item_id in (select min(item_id) from t_source t2 where t1.created_time=t2.created_time and t1.item_name=t2.item_name);
本次用时19秒,查询计划如下:
mysql> explain select distinct t1.* from t_source t1 where item_id in -> (select min(item_id) from t_source t2 where t1.created_time=t2.created_time and t1.item_name=t2.item_name); +----+--------------------+-------+------------+------+---------------+----------+---------+----------------------------------------+--------+----------+------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+--------------------+-------+------------+------+---------------+----------+---------+----------------------------------------+--------+----------+------------------------------+ | 1 | PRIMARY | t1 | NULL | ALL | NULL | NULL | NULL | NULL | 997281 | 100.00 | Using where; Using temporary | | 2 | DEPENDENT SUBQUERY | t2 | NULL | ref | idx_sort | idx_sort | 89 | test.t1.created_time,test.t1.item_name | 2 | 100.00 | Using index | +----+--------------------+-------+------------+------+---------------+----------+---------+----------------------------------------+--------+----------+------------------------------+ 2 rows in set, 3 warnings (0.00 sec)
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truncate t_target; insert into t_target select distinct t1.* from t_source t1, (select min(item_id) item_id,created_time,item_name from t_source group by created_time,item_name) t2 where t1.item_id = t2.item_id;
本次用时13秒,查询计划如下:
mysql> explain select distinct t1.* from t_source t1, -> (select min(item_id) item_id,created_time,item_name from t_source group by created_time,item_name) t2 -> where t1.item_id = t2.item_id; +----+-------------+------------+------------+-------+---------------+-------------+---------+-----------------+--------+----------+------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+------------+------------+-------+---------------+-------------+---------+-----------------+--------+----------+------------------------------+ | 1 | PRIMARY | t1 | NULL | ALL | NULL | NULL | NULL | NULL | 997281 | 100.00 | Using where; Using temporary | | 1 | PRIMARY | <derived2> | NULL | ref | <auto_key0> | <auto_key0> | 5 | test.t1.item_id | 10 | 100.00 | Distinct | | 2 | DERIVED | t_source | NULL | index | idx_sort | idx_sort | 94 | NULL | 997281 | 100.00 | Using index | +----+-------------+------------+------------+-------+---------------+-------------+---------+-----------------+--------+----------+------------------------------+ 3 rows in set, 1 warning (0.00 sec)
和没有索引相比,子查询虽然从全表扫描变为了全索引扫描,但还是需要扫描100万行记录。因此查询性能提升并不是明显。
(3)使用变量
set @a:='1000-01-01 00:00:00'; set @b:=' '; set @f:=0; truncate t_target; insert into t_target select item_id,created_time,modified_time,item_name,other from (select t0.*,if(@a=created_time and @b=item_name,@f:=0,@f:=1) f, @a:=created_time,@b:=item_name from (select * from t_source order by created_time,item_name) t0) t1 where f=1;
本次用时13秒,查询计划与没有索引时的完全相同。可见索引对这种写法没有作用。能不能消除嵌套,只用一层查询出结果呢?
(4)使用变量,并且消除嵌套查询
set @a:='1000-01-01 00:00:00'; set @b:=' '; truncate t_target; insert into t_target select * from t_source force index (idx_sort) where (@a!=created_time or @b!=item_name) and (@a:=created_time) is not null and (@b:=item_name) is not null order by created_time,item_name;
本次用时12秒,查询计划如下:
mysql> explain select * from t_source force index (idx_sort) -> where (@a!=created_time or @b!=item_name) and (@a:=created_time) is not null and (@b:=item_name) is not null -> order by created_time,item_name; +----+-------------+----------+------------+-------+---------------+----------+---------+------+--------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+----------+------------+-------+---------------+----------+---------+------+--------+----------+-------------+ | 1 | SIMPLE | t_source | NULL | index | NULL | idx_sort | 94 | NULL | 997281 | 99.00 | Using where | +----+-------------+----------+------------+-------+---------------+----------+---------+------+--------+----------+-------------+ 1 row in set, 3 warnings (0.00 sec)
该语句具有以下特点:
"color: #ff0000">二、利用窗口函数
MySQL 8中新增的窗口函数使得原来麻烦的去重操作变得很简单。
truncate t_target; insert into t_target select item_id, created_time, modified_time, item_name, other from (select *, row_number() over(partition by created_time,item_name) as rn from t_source) t where rn=1;
这个语句执行只需要12秒,而且写法清晰易懂,其查询计划如下:
mysql> explain select item_id, created_time, modified_time, item_name, other -> from (select *, row_number() over(partition by created_time,item_name) as rn -> from t_source) t where rn=1; +----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+----------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+----------------+ | 1 | PRIMARY | <derived2> | NULL | ref | <auto_key0> | <auto_key0> | 8 | const | 10 | 100.00 | NULL | | 2 | DERIVED | t_source | NULL | ALL | NULL | NULL | NULL | NULL | 997281 | 100.00 | Using filesort | +----+-------------+------------+------------+------+---------------+-------------+---------+-------+--------+----------+----------------+ 2 rows in set, 2 warnings (0.00 sec)
该查询对t_source表进行了一次全表扫描,同时用filesort对表按分区字段created_time、item_name进行了排序。外层查询从每个分区中保留一条数据。因为重复created_time
和item_name
的多条数据中可以保留任意一条,所以oevr中不需要使用order by子句。
从执行计划看,窗口函数去重语句似乎没有消除嵌套查询的变量去重好,但此方法实际执行是最快的。
MySQL窗口函数说明参见“https://dev.mysql.com/doc/refman/8.0/en/window-functions.html”。
三、多线程并行执行
前面已经将单条查重语句调整到最优,但还是以单线程方式执行。能否利用多处理器,让去重操作多线程并行执行,从而进一步提高速度呢?比如我的实验环境是4处理器,如果使用4个线程同时执行查重SQL,理论上应该接近4倍的性能提升。
1. 数据分片
在生成测试数据时,created_time采用每条记录加一秒的方式,也就是最大和在最小的时间差为50万秒,而且数据均匀分布,因此先把数据平均分成4份。
(1)查询出4份数据的created_time边界值
mysql> select date_add('2017-01-01',interval 125000 second) dt1, -> date_add('2017-01-01',interval 2*125000 second) dt2, -> date_add('2017-01-01',interval 3*125000 second) dt3, -> max(created_time) dt4 -> from t_source; +---------------------+---------------------+---------------------+---------------------+ | dt1 | dt2 | dt3 | dt4 | +---------------------+---------------------+---------------------+---------------------+ | 2017-01-02 10:43:20 | 2017-01-03 21:26:40 | 2017-01-05 08:10:00 | 2017-01-06 18:53:20 | +---------------------+---------------------+---------------------+---------------------+ 1 row in set (0.00 sec)
(2)查看每份数据的记录数,确认数据平均分布
mysql> select case when created_time >= '2017-01-01' -> and created_time < '2017-01-02 10:43:20' -> then '2017-01-01' -> when created_time >= '2017-01-02 10:43:20' -> and created_time < '2017-01-03 21:26:40' -> then '2017-01-02 10:43:20' -> when created_time >= '2017-01-03 21:26:40' -> and created_time < '2017-01-05 08:10:00' -> then '2017-01-03 21:26:40' -> else '2017-01-05 08:10:00' -> end min_dt, -> case when created_time >= '2017-01-01' -> and created_time < '2017-01-02 10:43:20' -> then '2017-01-02 10:43:20' -> when created_time >= '2017-01-02 10:43:20' -> and created_time < '2017-01-03 21:26:40' -> then '2017-01-03 21:26:40' -> when created_time >= '2017-01-03 21:26:40' -> and created_time < '2017-01-05 08:10:00' -> then '2017-01-05 08:10:00' -> else '2017-01-06 18:53:20' -> end max_dt, -> count(*) -> from t_source -> group by case when created_time >= '2017-01-01' -> and created_time < '2017-01-02 10:43:20' -> then '2017-01-01' -> when created_time >= '2017-01-02 10:43:20' -> and created_time < '2017-01-03 21:26:40' -> then '2017-01-02 10:43:20' -> when created_time >= '2017-01-03 21:26:40' -> and created_time < '2017-01-05 08:10:00' -> then '2017-01-03 21:26:40' -> else '2017-01-05 08:10:00' -> end, -> case when created_time >= '2017-01-01' -> and created_time < '2017-01-02 10:43:20' -> then '2017-01-02 10:43:20' -> when created_time >= '2017-01-02 10:43:20' -> and created_time < '2017-01-03 21:26:40' -> then '2017-01-03 21:26:40' -> when created_time >= '2017-01-03 21:26:40' -> and created_time < '2017-01-05 08:10:00' -> then '2017-01-05 08:10:00' -> else '2017-01-06 18:53:20' -> end; +---------------------+---------------------+----------+ | min_dt | max_dt | count(*) | +---------------------+---------------------+----------+ | 2017-01-01 | 2017-01-02 10:43:20 | 249999 | | 2017-01-02 10:43:20 | 2017-01-03 21:26:40 | 250000 | | 2017-01-03 21:26:40 | 2017-01-05 08:10:00 | 250000 | | 2017-01-05 08:10:00 | 2017-01-06 18:53:20 | 250002 | +---------------------+---------------------+----------+ 4 rows in set (4.86 sec)
4份数据的并集应该覆盖整个源数据集,并且数据之间是不重复的。也就是说4份数据的created_time要连续且互斥,连续保证处理全部数据,互斥确保了不需要二次查重。实际上这和时间范围分区的概念类似,或许用分区表更好些,只是这里省略了重建表的步骤。
2. 建立查重的存储过程
有了以上信息我们就可以写出4条语句处理全部数据。为了调用接口尽量简单,建立下面的存储过程。
delimiter // create procedure sp_unique(i smallint) begin set @a:='1000-01-01 00:00:00'; set @b:=' '; if (i<4) then insert into t_target select * from t_source force index (idx_sort) where created_time >= date_add('2017-01-01',interval (i-1)*125000 second) and created_time < date_add('2017-01-01',interval i*125000 second) and (@a!=created_time or @b!=item_name) and (@a:=created_time) is not null and (@b:=item_name) is not null order by created_time,item_name; else insert into t_target select * from t_source force index (idx_sort) where created_time >= date_add('2017-01-01',interval (i-1)*125000 second) and created_time <= date_add('2017-01-01',interval i*125000 second) and (@a!=created_time or @b!=item_name) and (@a:=created_time) is not null and (@b:=item_name) is not null order by created_time,item_name; end if; end //
查询语句的执行计划如下:
mysql> explain select * from t_source force index (idx_sort) -> where created_time >= date_add('2017-01-01',interval (1-1)*125000 second) -> and created_time < date_add('2017-01-01',interval 1*125000 second) -> and (@a!=created_time or @b!=item_name) -> and (@a:=created_time) is not null -> and (@b:=item_name) is not null -> order by created_time,item_name; +----+-------------+----------+------------+-------+---------------+----------+---------+------+--------+----------+-----------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+----------+------------+-------+---------------+----------+---------+------+--------+----------+-----------------------+ | 1 | SIMPLE | t_source | NULL | range | idx_sort | idx_sort | 6 | NULL | 498640 | 100.00 | Using index condition | +----+-------------+----------+------------+-------+---------------+----------+---------+------+--------+----------+-----------------------+ 1 row in set, 3 warnings (0.00 sec)
MySQL优化器进行索引范围扫描,并且使用索引条件下推(ICP)优化查询。
3. 并行执行
下面分别使用shell后台进程和MySQL Schedule Event实现并行。
(1)shell后台进程
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#!/bin/bash mysql -vvv -u root -p123456 test -e "truncate t_target" &>/dev/null date '+%H:%M:%S' for y in {1..4} do sql="call sp_unique($y)" mysql -vvv -u root -p123456 test -e "$sql" &>par_sql1_$y.log & done wait date '+%H:%M:%S'
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[mysql@hdp2~]$./duplicate_removal.sh 14:27:30 14:27:35
这种方法用时5秒,并行执行的4个过程调用分别用时为4.87秒、4.88秒、4.91秒、4.73秒:
[mysql@hdp2~]$cat par_sql1_1.log | sed '/^$/d' mysql: [Warning] Using a password on the command line interface can be insecure. -------------- call sp_unique(1) -------------- Query OK, 124999 rows affected (4.87 sec) Bye [mysql@hdp2~]$cat par_sql1_2.log | sed '/^$/d' mysql: [Warning] Using a password on the command line interface can be insecure. -------------- call sp_unique(2) -------------- Query OK, 125000 rows affected (4.88 sec) Bye [mysql@hdp2~]$cat par_sql1_3.log | sed '/^$/d' mysql: [Warning] Using a password on the command line interface can be insecure. -------------- call sp_unique(3) -------------- Query OK, 125000 rows affected (4.91 sec) Bye [mysql@hdp2~]$cat par_sql1_4.log | sed '/^$/d' mysql: [Warning] Using a password on the command line interface can be insecure. -------------- call sp_unique(4) -------------- Query OK, 125001 rows affected (4.73 sec) Bye [mysql@hdp2~]$
可以看到,每个过程的执行时间均4.85,因为是并行执行,总的过程执行时间为最慢的4.91秒,比单线程速度提高了2.5倍。
(2)MySQL Schedule Event
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-- 用于查看事件执行时间等信息 create table t_event_history ( dbname varchar(128) not null default '', eventname varchar(128) not null default '', starttime datetime(3) not null default '1000-01-01 00:00:00', endtime datetime(3) default null, issuccess int(11) default null, duration int(11) default null, errormessage varchar(512) default null, randno int(11) default null );
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delimiter // create event ev1 on schedule at current_timestamp + interval 1 hour on completion preserve disable do begin declare r_code char(5) default '00000'; declare r_msg text; declare v_error integer; declare v_starttime datetime default now(3); declare v_randno integer default floor(rand()*100001); insert into t_event_history (dbname,eventname,starttime,randno) #作业名 values(database(),'ev1', v_starttime,v_randno); begin #异常处理段 declare continue handler for sqlexception begin set v_error = 1; get diagnostics condition 1 r_code = returned_sqlstate , r_msg = message_text; end; #此处为实际调用的用户程序过程 call sp_unique(1); end; update t_event_history set endtime=now(3),issuccess=isnull(v_error),duration=timestampdiff(microsecond,starttime,now(3)), errormessage=concat('error=',r_code,', message=',r_msg),randno=null where starttime=v_starttime and randno=v_randno; end // create event ev2 on schedule at current_timestamp + interval 1 hour on completion preserve disable do begin declare r_code char(5) default '00000'; declare r_msg text; declare v_error integer; declare v_starttime datetime default now(3); declare v_randno integer default floor(rand()*100001); insert into t_event_history (dbname,eventname,starttime,randno) #作业名 values(database(),'ev2', v_starttime,v_randno); begin #异常处理段 declare continue handler for sqlexception begin set v_error = 1; get diagnostics condition 1 r_code = returned_sqlstate , r_msg = message_text; end; #此处为实际调用的用户程序过程 call sp_unique(2); end; update t_event_history set endtime=now(3),issuccess=isnull(v_error),duration=timestampdiff(microsecond,starttime,now(3)), errormessage=concat('error=',r_code,', message=',r_msg),randno=null where starttime=v_starttime and randno=v_randno; end // create event ev3 on schedule at current_timestamp + interval 1 hour on completion preserve disable do begin declare r_code char(5) default '00000'; declare r_msg text; declare v_error integer; declare v_starttime datetime default now(3); declare v_randno integer default floor(rand()*100001); insert into t_event_history (dbname,eventname,starttime,randno) #作业名 values(database(),'ev3', v_starttime,v_randno); begin #异常处理段 declare continue handler for sqlexception begin set v_error = 1; get diagnostics condition 1 r_code = returned_sqlstate , r_msg = message_text; end; #此处为实际调用的用户程序过程 call sp_unique(3); end; update t_event_history set endtime=now(3),issuccess=isnull(v_error),duration=timestampdiff(microsecond,starttime,now(3)), errormessage=concat('error=',r_code,', message=',r_msg),randno=null where starttime=v_starttime and randno=v_randno; end // create event ev4 on schedule at current_timestamp + interval 1 hour on completion preserve disable do begin declare r_code char(5) default '00000'; declare r_msg text; declare v_error integer; declare v_starttime datetime default now(3); declare v_randno integer default floor(rand()*100001); insert into t_event_history (dbname,eventname,starttime,randno) #作业名 values(database(),'ev4', v_starttime,v_randno); begin #异常处理段 declare continue handler for sqlexception begin set v_error = 1; get diagnostics condition 1 r_code = returned_sqlstate , r_msg = message_text; end; #此处为实际调用的用户程序过程 call sp_unique(4); end; update t_event_history set endtime=now(3),issuccess=isnull(v_error),duration=timestampdiff(microsecond,starttime,now(3)), errormessage=concat('error=',r_code,', message=',r_msg),randno=null where starttime=v_starttime and randno=v_randno; end //
为了记录每个事件执行的时间,在事件定义中增加了操作日志表的逻辑,因为每个事件中只多执行了一条insert,一条update,4个事件总共多执行8条很简单的语句,对测试的影响可以忽略不计。执行时间精确到毫秒。
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mysql -vvv -u root -p123456 test -e "truncate t_target;alter event ev1 on schedule at current_timestamp enable;alter event ev2 on schedule at current_timestamp enable;alter event ev3 on schedule at current_timestamp enable;alter event ev4 on schedule at current_timestamp enable;"
该命令行顺序触发了4个事件,但不会等前一个执行完才执行下一个,而是立即向下执行。这可从命令的输出可以清除看到:
[mysql@hdp2~]$mysql -vvv -u root -p123456 test -e "truncate t_target;alter event ev1 on schedule at current_timestamp enable;alter event ev2 on schedule at current_timestamp enable;alter event ev3 on schedule at current_timestamp enable;alter event ev4 on schedule at current_timestamp enable;" mysql: [Warning] Using a password on the command line interface can be insecure. -------------- truncate t_target -------------- Query OK, 0 rows affected (0.06 sec) -------------- alter event ev1 on schedule at current_timestamp enable -------------- Query OK, 0 rows affected (0.02 sec) -------------- alter event ev2 on schedule at current_timestamp enable -------------- Query OK, 0 rows affected (0.00 sec) -------------- alter event ev3 on schedule at current_timestamp enable -------------- Query OK, 0 rows affected (0.02 sec) -------------- alter event ev4 on schedule at current_timestamp enable -------------- Query OK, 0 rows affected (0.00 sec) Bye [mysql@hdp2~]$
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mysql> select * from test.t_event_history; +--------+-----------+-------------------------+-------------------------+-----------+----------+--------------+--------+ | dbname | eventname | starttime | endtime | issuccess | duration | errormessage | randno | +--------+-----------+-------------------------+-------------------------+-----------+----------+--------------+--------+ | test | ev1 | 2019-07-31 14:38:04.000 | 2019-07-31 14:38:09.389 | 1 | 5389000 | NULL | NULL | | test | ev2 | 2019-07-31 14:38:04.000 | 2019-07-31 14:38:09.344 | 1 | 5344000 | NULL | NULL | | test | ev3 | 2019-07-31 14:38:05.000 | 2019-07-31 14:38:09.230 | 1 | 4230000 | NULL | NULL | | test | ev4 | 2019-07-31 14:38:05.000 | 2019-07-31 14:38:09.344 | 1 | 4344000 | NULL | NULL | +--------+-----------+-------------------------+-------------------------+-----------+----------+--------------+--------+ 4 rows in set (0.00 sec)
可以看到,每个过程的执行均为4.83秒,又因为是并行执行的,因此总的执行之间为最慢的5.3秒,优化效果和shell后台进程方式几乎相同。
总结
以上所述是小编给大家介绍的将MySQL去重操作优化到极致的操作方法,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对网站的支持!
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