[toc] --- ## 背景 應用端需要生成依次遞增的序列來做流水序號等，方案有1、redis /MySQL SEQUENCE引擎生成序列；2、MySQL中myisam表 replace into方式；3、MySQL中innodb表INSERT ... ON DUPLICATE KEY方式 ## 分析 - redis /MySQL SEQUENCE引擎生成序列，但多個MySQL叢集都有生成序列的需求，若出問題，影響範圍大；redis /MySQL SEQUENCE中生成序列也增加了研發修改程式碼的成本，新專案可以使用這種方式 --- - MySQL中myisam表 replace into 是我們目前使用生成序列的方式（雖然是表鎖，每秒生成的序列也滿足得了需求），使用方式為 ``` CREATE TABLE `test_sequence` ( `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT, `val` tinyint(1) DEFAULT '0', PRIMARY KEY (`id`), UNIQUE KEY `val` (`val`) ) ENGINE=MyISAM; >replace into test_sequence(val) values(99); Query OK, 1 row affected (0.00 sec) >select last_insert_id(); +------------------+ | last_insert_id() | +------------------+ | 1 | +------------------+ 1 row in set (0.00 sec) >replace into test_sequence(val) values(99); Query OK, 2 rows affected (0.00 sec) >select last_insert_id(); +------------------+ | last_insert_id() | +------------------+ | 2 | +------------------+ 1 row in set (0.00 sec) ``` > 但存在問題： > myisam表非事務儲存引擎，備份存在不一致（恢復還原資料有不一致風險）； > myisam也不是crash-safe的； > gtid模式下，同一個事務中不能操作myisam表和innodb表 > > 為什麼不用innodb表replace into方式了？ > 該方式併發大時，存在發生死鎖的風險 --- - MySQL中事務性 innodb表INSERT ... ON DUPLICATE KEY，是crash-safe ，看起來myisam生成序列的存在的問題它都沒有！實際情況了？ 使用方式： ``` CREATE TABLE `test_sequence2` ( `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT, `val` tinyint(1) DEFAULT '0', PRIMARY KEY (`id`), UNIQUE KEY `val` (`val`) ) ENGINE=InnoDB; 00>insert into test_sequence2(val) values(99) on duplicate key update id=id+1; Query OK, 1 row affected (0.00 sec) 39>select id from test_sequence2; +---------+ | id | +---------+ | 1 | +---------+ 1 row in set (0.00 sec) 22>insert into test_sequence2(val) values(99) on duplicate key update id=id+1; Query OK, 2 rows affected (0.00 sec) 25>select id from test_sequence2; +---------+ | id | +---------+ | 2 | +---------+ 1 row in set (0.00 sec) ``` ## 測試 普通機械磁碟機器 MySQL5.7.16 RR隔離級別 sysbench 自定義sql語句測試tps（每秒生成多少序列） - myisam replace into 方式 ``` cd /usr/share/sysbench/tests sysbench ./test_myisam.lua --mysql-host=127.0.0.1 --mysql-port=3701 --mysql-db=test --mysql-user=sysbench --mysql-password=sysbench --tables=1 --threads=10 --time=30 --report-interval=5 run ``` - innodb INSERT ... ON DUPLICATE KEY UPDATE方式 ``` cd /usr/share/sysbench/tests sysbench ./test_innodb.lua --mysql-host=127.0.0.1 --mysql-port=3701 --mysql-db=test --mysql-user=sysbench --mysql-password=sysbench --tables=1 --threads=10 --time=30 --report-interval=5 run ``` | |myisam replace into |innodb insert..on duplicate | | --- | --- | --- | | 1併發執行緒 | 124 tps | 122 tps | | 10併發執行緒 | 123 tps | 121 tps | |20併發執行緒 | 125 tps |104 tps | |30併發執行緒 |127 tps |67 tps | |40併發執行緒 |127 tps | 33 tps | - **可見myisam隨著併發執行緒數的增加，replace into tps保持不變，原因是myisam是表鎖，同一時刻，該表只能寫或者只能讀** - **innodb表隨著併發數的上升，insert..on duplicate tps不升反降，行鎖之前的爭用變大了 造成鎖等待** - **本次測試機器配置差，結果有些參考性，線上機器配置更好** --- ***注意 mysqlslap 壓測innodb表40個併發執行緒時可能會出現死鎖（RC隔離級別也是），死鎖詳細見最後*** ***為什麼sysbench40 併發執行緒測試沒有出現過死鎖？難道sysbench併發執行緒不是同一時刻發出的？~_~*** ``` /usr/local/mysql/bin/mysqlslap -usysbench -h127.0.0.1 -P3701 -p --concurrency=40 --iterations=1 --create-schema=test --query='insert into test_sequence2(val) values(99) on duplicate key update id=id+1;select id from test_sequence2;' /usr/local/mysql/bin/mysqlslap: Cannot run query insert into test_sequence2(val) values(99) on duplicate key update id=id+1;select id from test_sequence2; ERROR : Deadlock found when trying to get lock; try restarting transaction ``` ## 結論 - ***myisam表 replace into生成序列是穩定的方法，不管併發執行緒數多少，生成序列速度是穩定的，但myisam表存在缺陷問題*** - ***innodb表 inert on duplicate 生成序列適合併發執行緒數少情況，併發執行緒數多會出現死鎖 生成序列速度下降情況*** - ***若要求生成序列的速度快，可用redis /MySQL SEQUENCE方式*** **死鎖日誌** ``` LATEST DETECTED DEADLOCK ------------------------ 2020-02-11 11:03:11 0x7f6a0c643700 *** (1) TRANSACTION: TRANSACTION 39260727, ACTIVE 1 sec inserting mysql tables in use 1, locked 1 LOCK WAIT 28 lock struct(s), heap size 3520, 26 row lock(s), undo log entries 1 MySQL thread id 460828, OS thread handle 140093451958016, query id 21296424 127.0.0.1 root update insert into test_sequence2(val) values(99) on duplicate key update id=id+1 *** (1) WAITING FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 48 page no 4 n bits 72 index val of table `test`.`test_sequence2` trx id 39260727 lock_mode X waiting Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 1; hex e3; asc ;; 1: len 8; hex 000000000000001a; asc ;; *** (2) TRANSACTION: TRANSACTION 39260729, ACTIVE 1 sec updating or deleting, thread declared inside InnoDB 5000 mysql tables in use 1, locked 1 29 lock struct(s), heap size 3520, 27 row lock(s), undo log entries 1 MySQL thread id 460835, OS thread handle 140093451155200, query id 21296425 127.0.0.1 root update insert into test_sequence2(val) values(99) on duplicate key update id=id+1 *** (2) HOLDS THE LOCK(S): RECORD LOCKS space id 48 page no 4 n bits 72 index val of table `test`.`test_sequence2` trx id 39260729 lock_mode X Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 1; hex e3; asc ;; 1: len 8; hex 000000000000001a; asc ;; *** (2) WAITING FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 48 page no 3 n bits 168 index PRIMARY of table `test`.`test_sequence2` trx id 39260729 lock_mode X waiting Record lock, heap no 37 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 8; hex 000000000000001b; asc ;; 1: len 6; hex 000002571237; asc W 7;; 2: len 7; hex b6000001680110; asc h ;; 3: len 1; hex e3; asc ;; *** WE ROLL BACK TRANSACTION (1) ``` **自定義sysbench指令碼** less test_myisam/innodb.lua ``` require("oltp_common") function thread_init(thread_id) drv=sysbench.sql.driver() con=drv:connect() end function event(thread_id) local vid1 local dbprefix con:query('replace into test_sequence(val) values(99)') con:query('select last_insert_id()') ##innodb insert..on duplicate 語句 #con:query('insert into test_sequence2(val) values(99) on duplicate key update id=id+1') #con:query('select id from test_sequence2;') end function thread_done() con:disconnect()