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一开工,就遇到上亿(MySQL)大表的优化,我的天...

作者:jiaxin

来源:https://www.cnblogs.com/YangJiaXin/p/10828244.html


# 背景


XX实例(一主一从)xxx告警中每天凌晨在报SLA报警,该报警的意思是存在一定的主从延迟(若在此时发生主从切换,需要长时间才可以完成切换,要追延迟来保证主从数据的一致性)


XX实例的慢查询数量最多(执行时间超过1s的sql会被记录),XX应用那方每天晚上在做删除一个月前数据的任务


# 分析


使用pt-query-digest工具分析最近一周的mysql-slow.log

pt-query-digest --since=148h mysql-slow.log | less

结果第一部分


最近一个星期内,总共记录的慢查询执行花费时间为25403s,最大的慢sql执行时间为266s,平均每个慢sql执行时间5s,平均扫描的行数为1766万。


结果第二部分

select arrival_record操作记录的慢查询数量最多有4万多次,平均响应时间为4s,delete arrival_record记录了6次,平均响应时间258s


# select xxx_record语句


select arrival_record 慢查询语句都类似于如下所示,where语句中的参数字段是一样的,传入的参数值不一样。

select count(*) from arrival_record where product_id=26 and receive_time between '2019-03-25 14:00:00' and '2019-03-25 15:00:00' and receive_spend_ms>=0\G



select arrival_record 语句在mysql中最多扫描的行数为5600万、平均扫描的行数为172万,推断由于扫描的行数多导致的执行时间长


查看执行计划

explain select count() from arrival_record where product_id=26 and receive_time between '2019-03-25 14:00:00' and '2019-03-25 15:00:00' and receive_spend_ms>=0\G;


************************** 1. row ***************************id: 1select_type: SIMPLEtable: arrival_recordpartitions: NULLtype: refpossible_keys: IXFK_arrival_recordkey: IXFK_arrival_recordkey_len: 8ref: constrows: 32261320filtered: 3.70Extra: Using index condition; Using where1 row in set, 1 warning (0.00 sec)


用到了索引IXFK_arrival_record,但预计扫描的行数很多有3000多w行

show index from arrival_record;+----------------+------------+---------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |+----------------+------------+---------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| arrival_record | 0 | PRIMARY | 1 | id | A | 107990720 | NULL | NULL | | BTREE | | || arrival_record | 1 | IXFK_arrival_record | 1 | product_id | A | 1344 | NULL | NULL | | BTREE | | || arrival_record | 1 | IXFK_arrival_record | 2 | station_no | A | 22161 | NULL | NULL | YES | BTREE | | || arrival_record | 1 | IXFK_arrival_record | 3 | sequence | A | 77233384 | NULL | NULL | | BTREE | | || arrival_record | 1 | IXFK_arrival_record | 4 | receive_time | A | 65854652 | NULL | NULL | YES | BTREE | | || arrival_record | 1 | IXFK_arrival_record | 5 | arrival_time | A | 73861904 | NULL | NULL | YES | BTREE | | |+----------------+------------+---------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
show create table arrival_record;..........arrival_spend_ms bigint(20) DEFAULT NULL,total_spend_ms bigint(20) DEFAULT NULL,PRIMARY KEY (id),KEY IXFK_arrival_record (product_id,station_no,sequence,receive_time,arrival_time) USING BTREE,CONSTRAINT FK_arrival_record_product FOREIGN KEY (product_id) REFERENCES product (id) ON DELETE NO ACTION ON UPDATE NO ACTION) ENGINE=InnoDB AUTO_INCREMENT=614538979 DEFAULT CHARSET=utf8 COLLATE=utf8_bin |---


  • 该表总记录数约1亿多条,表上只有一个复合索引,product_id字段基数很小,选择性不好

  • 传入的过滤条件 where product_id=26 and receive_time between '2019-03-25 14:00:00' and '2019-03-25 15:00:00' and receive_spend_ms>=0 没有station_nu字段,使用不到复合索引 IXFK_arrival_record的 product_id,station_no,sequence,receive_time 这几个字段

  • 根据最左前缀原则,select arrival_record只用到了复合索引IXFK_arrival_record的第一个字段product_id,而该字段选择性很差,导致扫描的行数很多,执行时间长

  • receive_time字段的基数大,选择性好,可对该字段单独建立索引,select arrival_record sql就会使用到该索引


现在已经知道了在慢查询中记录的select arrival_record where语句传入的参数字段有 product_id,receive_time,receive_spend_ms,还想知道对该表的访问有没有通过其它字段来过滤了?


# 神器tcpdump出场的时候到了


使用tcpdump抓包一段时间对该表的select语句

tcpdump -i bond0 -s 0 -l -w - dst port 3316 | strings | grep select | egrep -i 'arrival_record' >/tmp/select_arri.log
获取select 语句中from 后面的where条件语句
IFS_OLD=$IFSIFS=$'\n'for i in `cat /tmp/select_arri.log `;do echo ${i#*'from'}; done | lessIFS=$IFS_OLD

arrival_record arrivalrec0_ where arrivalrec0_.sequence='2019-03-27 08:40' and arrivalrec0_.product_id=17 and arrivalrec0_.station_no='56742'arrival_record arrivalrec0_ where arrivalrec0_.sequence='2019-03-27 08:40' and arrivalrec0_.product_id=22 and arrivalrec0_.station_no='S7100'arrival_record arrivalrec0_ where arrivalrec0_.sequence='2019-03-27 08:40' and arrivalrec0_.product_id=24 and arrivalrec0_.station_no='V4631'arrival_record arrivalrec0_ where arrivalrec0_.sequence='2019-03-27 08:40' and arrivalrec0_.product_id=22 and arrivalrec0_.station_no='S9466'arrival_record arrivalrec0_ where arrivalrec0_.sequence='2019-03-27 08:40' and arrivalrec0_.product_id=24 and arrivalrec0_.station_no='V4205'arrival_record arrivalrec0_ where arrivalrec0_.sequence='2019-03-27 08:40' and arrivalrec0_.product_id=24 and arrivalrec0_.station_no='V4105'arrival_record arrivalrec0_ where arrivalrec0_.sequence='2019-03-27 08:40' and arrivalrec0_.product_id=24 and arrivalrec0_.station_no='V4506'arrival_record arrivalrec0_ where arrivalrec0_.sequence='2019-03-27 08:40' and arrivalrec0_.product_id=24 and arrivalrec0_.station_no='V4617'arrival_record arrivalrec0_ where arrivalrec0_.sequence='2019-03-27 08:40' and arrivalrec0_.product_id=22 and arrivalrec0_.station_no='S8356'arrival_record arrivalrec0_ where arrivalrec0_.sequence='2019-03-27 08:40' and arrivalrec0_.product_id=22 and arrivalrec0_.station_no='S8356'


  • select 该表 where条件中有product_id,station_no,sequence字段,可以使用到复合索引IXFK_arrival_record的前三个字段。


综上所示,优化方法为,删除复合索引IXFK_arrival_record,建立复合索引idx_sequence_station_no_product_id,并建立单独索引indx_receive_time。


# delete xxx_record语句


该delete操作平均扫描行数为1.1亿行,平均执行时间是262s

delete语句如下所示,每次记录的慢查询传入的参数值不一样

delete from arrival_record where receive_time < STR_TO_DATE('2019-02-23', '%Y-%m-%d')\G


执行计划

explain select * from arrival_record where receive_time < STR_TO_DATE('2019-02-23', '%Y-%m-%d')\G*************************** 1. row ***************************id: 1select_type: SIMPLEtable: arrival_recordpartitions: NULLtype: ALLpossible_keys: NULLkey: NULLkey_len: NULLref: NULLrows: 109501508filtered: 33.33Extra: Using where1 row in set, 1 warning (0.00 sec)


  • 该delete语句没有使用索引(没有合适的索引可用),走的全表扫描,导致执行时间长

  • 优化方法也是 建立单独索引indx_receive_time(receive_time)


# 测试


拷贝arrival_record表到测试实例上进行删除重新索引操作
XX实例arrival_record表信息

du -sh /datas/mysql/data/3316/cq_new_cimiss/arrival_record*12K /datas/mysql/data/3316/cq_new_cimiss/arrival_record.frm48G /datas/mysql/data/3316/cq_new_cimiss/arrival_record.ibd

select count() from cq_new_cimiss.arrival_record;+-----------+| count() |+-----------+| 112294946 |+-----------+1亿多记录数

SELECTtable_name,CONCAT(FORMAT(SUM(data_length) / 1024 / 1024,2),'M') AS dbdata_size,CONCAT(FORMAT(SUM(index_length) / 1024 / 1024,2),'M') AS dbindex_size,CONCAT(FORMAT(SUM(data_length + index_length) / 1024 / 1024 / 1024,2),'G') AS table_size(G),AVG_ROW_LENGTH,table_rows,update_timeFROMinformation_schema.tablesWHERE table_schema = 'cq_new_cimiss' and table_name='arrival_record';


+----------------+-------------+--------------+------------+----------------+------------+---------------------+| table_name | dbdata_size | dbindex_size | table_size(G) | AVG_ROW_LENGTH | table_rows | update_time |+----------------+-------------+--------------+------------+----------------+------------+---------------------+| arrival_record | 18,268.02M | 13,868.05M | 31.38G | 175 | 109155053 | 2019-03-26 12:40:17 |+----------------+-------------+--------------+------------+----------------+------------+---------------------+

磁盘占用空间48G,mysql中该表大小为31G,存在17G左右的碎片,大多由于删除操作造成的(记录被删除了,空间没有回收)。


备份还原该表到新的实例中,删除原来的复合索引,重新添加索引进行测试。


mydumper并行压缩备份。

user=root passwd=xxxx socket=/datas/mysql/data/3316/mysqld.sock db=cq_new_cimiss table_name=arrival_record backupdir=/datas/dump_$table_name mkdir -p $backupdir
nohup echo `date +%T` && mydumper -u $user -p $passwd -S $socket -B $db -c -T $table_name -o $backupdir -t 32 -r 2000000 && echo `date +%T`


并行压缩备份所花时间(52s)和占用空间(1.2G,实际该表占用磁盘空间为48G,mydumper并行压缩备份压缩比相当高!)

Started dump at: 2019-03-26 12:46:04........
Finished dump at: 2019-03-26 12:46:56
du -sh /datas/dump_arrival_record/1.2G /datas/dump_arrival_record/

拷贝dump数据到测试节点

scp -rp /datas/dump_arrival_record root@10.230.124.19:/datas


多线程导入数据

time myloader -u root -S /datas/mysql/data/3308/mysqld.sock -P 3308 -p root -B test -d /datas/dump_arrival_record -t 32


real 126m42.885suser 1m4.543ssys 0m4.267s


逻辑导入该表后磁盘占用空间

du -h -d 1 /datas/mysql/data/3308/test/arrival_record.12K /datas/mysql/data/3308/test/arrival_record.frm30G /datas/mysql/data/3308/test/arrival_record.ibd

没有碎片,和mysql的该表的大小一致。


cp -rp /datas/mysql/data/3308 /datas

分别使用online DDL和 pt-osc工具来做删除重建索引操作


先删除外键,不删除外键,无法删除复合索引,外键列属于复合索引中第一列。

nohup bash /tmp/ddl_index.sh &2019-04-04-10:41:39 begin stop mysqld_33082019-04-04-10:41:41 begin rm -rf datadir and cp -rp datadir_bak2019-04-04-10:46:53 start mysqld_33082019-04-04-10:46:59 online ddl begin2019-04-04-11:20:34 onlie ddl stop2019-04-04-11:20:34 begin stop mysqld_33082019-04-04-11:20:36 begin rm -rf datadir and cp -rp datadir_bak2019-04-04-11:22:48 start mysqld_33082019-04-04-11:22:53 pt-osc begin2019-04-04-12:19:15 pt-osc stop

online ddl 花费时间为34 分钟,pt-osc花费时间为57 分钟,使用onlne ddl时间约为pt-osc工具时间的一半。



# 实施


由于是一主一从实例,应用是连接的vip,删除重建索引采用online ddl来做。停止主从复制后,先在从实例上做(不记录binlog),主从切换,再在新切换的从实例上做(不记录binlog)

function red_echo () {
local what="$*" echo -e "$(date +%F-%T) ${what}"}
function check_las_comm(){ if [ "$1" != "0" ];then red_echo "$2" echo "exit 1" exit 1 fi}
red_echo "stop slave"mysql -uroot -p$passwd --socket=/datas/mysql/data/${port}/mysqld.sock -e"stop slave"check_las_comm "$?" "stop slave failed"
red_echo "online ddl begin" mysql -uroot -p$passwd --socket=/datas/mysql/data/${port}/mysqld.sock -e"set sql_log_bin=0;select now() as ddl_start;ALTER TABLE $db_.\`${table_name}\` DROP FOREIGN KEY FK_arrival_record_product,drop index IXFK_arrival_record,add index idx_product_id_sequence_station_no(product_id,sequence,station_no),add index idx_receive_time(receive_time);select now() as ddl_stop" >>${log_file} 2>& 1 red_echo "onlie ddl stop" red_echo "add foreign key" mysql -uroot -p$passwd --socket=/datas/mysql/data/${port}/mysqld.sock -e"set sql_log_bin=0;ALTER TABLE $db_.${table_name} ADD CONSTRAINT _FK_${table_name}_product FOREIGN KEY (product_id) REFERENCES cq_new_cimiss.product (id) ON DELETE NO ACTION ON UPDATE NO ACTION;" >>${log_file} 2>& 1 check_las_comm "$?" "add foreign key error" red_echo "add foreign key stop"
red_echo "start slave"mysql -uroot -p$passwd --socket=/datas/mysql/data/${port}/mysqld.sock -e"start slave"check_las_comm "$?" "start slave failed"

执行时间

2019-04-08-11:17:36 stop slavemysql: [Warning] Using a password on the command line interface can be insecure.ddl_start2019-04-08 11:17:36ddl_stop2019-04-08 11:45:132019-04-08-11:45:13 onlie ddl stop2019-04-08-11:45:13 add foreign keymysql: [Warning] Using a password on the command line interface can be insecure.2019-04-08-12:33:48 add foreign key stop2019-04-08-12:33:48 start slave

删除重建索引花费时间为28分钟,添加外键约束时间为48分钟。


再次查看delete 和select语句的执行计划

explain select count() from arrival_record where receive_time < STR_TO_DATE('2019-03-10', '%Y-%m-%d')\G************************** 1. row ***************************id: 1select_type: SIMPLEtable: arrival_recordpartitions: NULLtype: rangepossible_keys: idx_receive_timekey: idx_receive_timekey_len: 6ref: NULLrows: 7540948filtered: 100.00Extra: Using where; Using index


explain select count() from arrival_record where product_id=26 and receive_time between '2019-03-25 14:00:00' and '2019-03-25 15:00:00' and receive_spend_ms>=0\G;************************** 1. row ***************************id: 1select_type: SIMPLEtable: arrival_recordpartitions: NULLtype: rangepossible_keys: idx_product_id_sequence_station_no,idx_receive_timekey: idx_receive_timekey_len: 6ref: NULLrows: 291448filtered: 16.66Extra: Using index condition; Using where

都使用到了idx_receive_time 索引,扫描的行数大大降低。


# 索引优化后


delete 还是花费了77s时间

delete from arrival_record where receive_time < STR_TO_DATE('2019-03-10', '%Y-%m-%d')\G

delete 语句通过receive_time的索引删除300多万的记录花费77s时间。


# delete大表优化为小批量删除


应用端已优化成每次删除10分钟的数据(每次执行时间1s左右),xxx中没在出现SLA(主从延迟告警)



另一个方法是通过主键的顺序每次删除20000条记录

#得到满足时间条件的最大主键ID#通过按照主键的顺序去 顺序扫描小批量删除数据#先执行一次以下语句 SELECT MAX(id) INTO @need_delete_max_id FROM `arrival_record` WHERE receive_time<'2019-03-01' ; DELETE FROM arrival_record WHERE id<@need_delete_max_id LIMIT 20000; select ROW_COUNT(); #返回20000

#执行小批量delete后会返回row_count(), 删除的行数#程序判断返回的row_count()是否为0,不为0执行以下循环,为0退出循环,删除操作完成 DELETE FROM arrival_record WHERE id<@need_delete_max_id LIMIT 20000; select ROW_COUNT();#程序睡眠0.5s


# 总结

  • 表数据量太大时,除了关注访问该表的响应时间外,还要关注对该表的维护成本(如做DDL表更时间太长,delete历史数据)

  • 对大表进行DDL操作时,要考虑表的实际情况(如对该表的并发表,是否有外键)来选择合适的DDL变更方式

  • 对大数据量表进行delete,用小批量删除的方式,减少对主实例的压力和主从延迟


 往期推荐 

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