遇到上亿(MySQL)大表的优化....
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背景
XX實(shí)例（一主一從）xxx告警中每天凌晨在報SLA報警，該報警的意思是存在一定的主從延遲（若在此時發(fā)生主從切換，需要長時間才可以完成切換，要追延遲來保證主從數(shù)據(jù)的一致性）
XX實(shí)例的慢查詢數(shù)量最多（執(zhí)行時間超過1s的sql會被記錄），XX應(yīng)用那方每天晚上在做刪除一個月前數(shù)據(jù)的任務(wù)
分析
使用pt-query-digest工具分析最近一周的mysql-slow.log
結(jié)果第一部分
最近一個星期內(nèi)，總共記錄的慢查詢執(zhí)行花費(fèi)時間為25403s，最大的慢sql執(zhí)行時間為266s，平均每個慢sql執(zhí)行時間5s，平均掃描的行數(shù)為1766萬
結(jié)果第二部分
select arrival_record操作記錄的慢查詢數(shù)量最多有4萬多次，平均響應(yīng)時間為4s，delete arrival_record記錄了6次，平均響應(yīng)時間258s。
select xxx_record語句
select arrival_record 慢查詢語句都類似于如下所示，where語句中的參數(shù)字段是一樣的，傳入的參數(shù)值不一樣
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 語句在mysql中最多掃描的行數(shù)為5600萬、平均掃描的行數(shù)為172萬，推斷由于掃描的行數(shù)多導(dǎo)致的執(zhí)行時間長
查看執(zhí)行計劃
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: 1 select_type: SIMPLE table: arrival_record partitions: NULL type: ref possible_keys: IXFK_arrival_record key: IXFK_arrival_record key_len: 8 ref: const rows: 32261320 filtered: 3.70 Extra: Using index condition; Using where 1?row in?set, 1?warning (0.00?sec)用到了索引IXFK_arrival_record，但預(yù)計掃描的行數(shù)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 |該表總記錄數(shù)約1億多條，表上只有一個復(fù)合索引，product_id字段基數(shù)很小，選擇性不好
傳入的過濾條件 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 沒有station_nu字段，使用不到復(fù)合索引 IXFK_arrival_record的?product_id,station_no,sequence,receive_time?這幾個字段
根據(jù)最左前綴原則，select arrival_record只用到了復(fù)合索引IXFK_arrival_record的第一個字段product_id，而該字段選擇性很差，導(dǎo)致掃描的行數(shù)很多，執(zhí)行時間長
receive_time字段的基數(shù)大，選擇性好，可對該字段單獨(dú)建立索引，select arrival_record sql就會使用到該索引
現(xiàn)在已經(jīng)知道了在慢查詢中記錄的select arrival_record where語句傳入的參數(shù)字段有 product_id，receive_time，receive_spend_ms，還想知道對該表的訪問有沒有通過其它字段來過濾了？
神器tcpdump出場的時候到了
使用tcpdump抓包一段時間對該表的select語句
tcpdump -i bond0 -s 0?-l?-w?- dst port 3316?| strings | grep?select | egrep -i 'arrival_record'?>/tmp/select_arri.log獲取select 語句中from 后面的where條件語句
IFS_OLD=$IFS IFS=$'\n' for?i in?`cat /tmp/select_arri.log `;do?echo?${i#*'from'}; done?| less IFS=$IFS_OLDarrival_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 該表 where條件中有product_id,station_no,sequence字段，可以使用到復(fù)合索引IXFK_arrival_record的前三個字段綜上所示，優(yōu)化方法為，刪除復(fù)合索引IXFK_arrival_record，建立復(fù)合索引idx_sequence_station_no_product_id，并建立單獨(dú)索引indx_receive_time
delete xxx_record語句
該delete操作平均掃描行數(shù)為1.1億行，平均執(zhí)行時間是262s
delete語句如下所示，每次記錄的慢查詢傳入的參數(shù)值不一樣
delete?from?arrival_record where?receive_time < STR_TO_DATE('2019-02-23', '%Y-%m-%d')\G執(zhí)行計劃
explain?select?* from?arrival_record where?receive_time < STR_TO_DATE('2019-02-23', '%Y-%m-%d')\G *************************** 1.?row?*************************** id: 1 select_type: SIMPLE table: arrival_record partitions: NULL type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 109501508 filtered: 33.33 Extra: Using?where 1?row?in?set, 1?warning?(0.00?sec)該delete語句沒有使用索引（沒有合適的索引可用），走的全表掃描，導(dǎo)致執(zhí)行時間長
優(yōu)化方法也是 建立單獨(dú)索引indx_receive_time(receive_time)
測試
拷貝arrival_record表到測試實(shí)例上進(jìn)行刪除重新索引操作
XX實(shí)例arrival_record表信息
磁盤占用空間48G，mysql中該表大小為31G，存在17G左右的碎片，大多由于刪除操作造成的（記錄被刪除了，空間沒有回收)
備份還原該表到新的實(shí)例中，刪除原來的復(fù)合索引，重新添加索引進(jìn)行測試
mydumper并行壓縮備份
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 $backupdir -t 32?-r 2000000?&& echo `date +%T`?&并行壓縮備份所花時間（52s）和占用空間（1.2G，實(shí)際該表占用磁盤空間為48G，mydumper并行壓縮備份壓縮比相當(dāng)高！）
Started?dump?at: 2019-03-26?12:46:04 ........Finished?dump?at: 2019-03-26?12:46:56du?-sh???/datas/dump_arrival_record/ 1.2G??/datas/dump_arrival_record/拷貝dump數(shù)據(jù)到測試節(jié)點(diǎn)
多線程導(dǎo)入數(shù)據(jù)
time myloader -u root -S /datas/mysql/data/3308/mysqld.sock -P 3308 -p root -B test?-d /datas/dump_arrival_record -t 32real 126m42.885s
user 1m4.543s
sys 0m4.267s
邏輯導(dǎo)入該表后磁盤占用空間
du -h -d 1 /datas/mysql/data/3308/test/arrival_record.* 12K /datas/mysql/data/3308/test/arrival_record.frm 30G /datas/mysql/data/3308/test/arrival_record.ibd 沒有碎片，和mysql的該表的大小一致cp?-rp /datas/mysql/data/3308?/datas分別使用online DDL和 pt-osc工具來做刪除重建索引操作
先刪除外鍵，不刪除外鍵，無法刪除復(fù)合索引，外鍵列屬于復(fù)合索引中第一列
做DDL 參考
實(shí)施
由于是一主一從實(shí)例，應(yīng)用是連接的vip，刪除重建索引采用online ddl來做。停止主從復(fù)制后，先在從實(shí)例上做（不記錄binlog），主從切換，再在新切換的從實(shí)例上做（不記錄binlog)
function red_echo () {local what="$*"echo -e "$(date +%F-%T) ${what}" }function check_las_comm(){if [ "$1" != "0" ];thenred_echo "$2"echo "exit 1"exit 1fi }red_echo "stop slave" mysql -uroot -p$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" >>${log_file} 2>& 1red_echo "onlie ddl stop"red_echo "add foreign key"mysql -uroot -p$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>& 1check_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"執(zhí)行時間
2019-04-08-11:17:36 stop slave
mysql: [Warning] Using a password on the command line interface can be insecure.
ddl_start
2019-04-08?11:17:36
ddl_stop
2019-04-08?11:45:13
2019-04-08-11:45:13 onlie ddl stop
2019-04-08-11:45:13?add foreign key
mysql: [Warning] Using a password on the command line interface can be insecure.
2019-04-08-12:33:48 add foreign key stop
2019-04-08-12:33:48?start slave
再次查看delete 和select語句的執(zhí)行計劃
explain select?count(*) from?arrival_record where?receive_time < STR_TO_DATE('2019-03-10', '%Y-%m-%d')\G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: arrival_record partitions: NULL type: range possible_keys: idx_receive_time key: idx_receive_time key_len: 6 ref: NULL rows: 7540948 filtered: 100.00 Extra: 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: 1 select_type: SIMPLE table: arrival_record partitions: NULL type: range possible_keys: idx_product_id_sequence_station_no,idx_receive_time key: idx_receive_time key_len: 6 ref: NULL rows: 291448 filtered: 16.66 Extra: Using index condition; Using where 都使用到了idx_receive_time 索引，掃描的行數(shù)大大降低索引優(yōu)化后
delete 還是花費(fèi)了77s時間
delete?from?arrival_record where?receive_time < STR_TO_DATE('2019-03-10', '%Y-%m-%d')\Gdelete 語句通過receive_time的索引刪除300多萬的記錄花費(fèi)77s時間*
delete大表優(yōu)化為小批量刪除
應(yīng)用端已優(yōu)化成每次刪除10分鐘的數(shù)據(jù)（每次執(zhí)行時間1s左右），xxx中沒在出現(xiàn)SLA（主從延遲告警）
另一個方法是通過主鍵的順序每次刪除20000條記錄
#得到滿足時間條件的最大主鍵ID #通過按照主鍵的順序去 順序掃描小批量刪除數(shù)據(jù) #先執(zhí)行一次以下語句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#執(zhí)行小批量delete后會返回row_count(), 刪除的行數(shù) #程序判斷返回的row_count()是否為0，不為0執(zhí)行以下循環(huán)，為0退出循環(huán)，刪除操作完成DELETE FROM arrival_record WHERE id<@need_delete_max_id LIMIT 20000;select ROW_COUNT(); #程序睡眠0.5s總結(jié)
表數(shù)據(jù)量太大時，除了關(guān)注訪問該表的響應(yīng)時間外，還要關(guān)注對該表的維護(hù)成本（如做DDL表更時間太長，delete歷史數(shù)據(jù)）。
對大表進(jìn)行DDL操作時，要考慮表的實(shí)際情況（如對該表的并發(fā)表，是否有外鍵）來選擇合適的DDL變更方式。
對大數(shù)據(jù)量表進(jìn)行delete，用小批量刪除的方式，減少對主實(shí)例的壓力和主從延遲。
作者：jia-xin
原文：https://www.cnblogs.com/YangJiaXin/p/10828244.html
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