MySQL MyISAM和Innodb表生成序列

目錄

• 背景
• 分析
• 測試
• 結論

---

背景

應用端須要生成依次遞增的序列來作流水序號等，方案有一、redis /MySQL SEQUENCE引擎生成序列；二、MySQL中myisam表 replace into方式；三、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集羣都有生成序列的需求，若出問題，影響範圍大；redis /MySQL SEQUENCE中生成序列也增長了研發修改代碼的成本，新項目可使用這種方式

---

• MySQL中myisam表 replace into 是咱們目前使用生成序列的方式（雖然是表鎖，每秒生成的序列也知足得了需求），使用方式爲

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表非事務存儲引擎，備份存在不一致（恢復還原數據有不一致風險）；
myisam也不是crash-safe的；
gtid模式下，同一個事務中不能操做myisam表和innodb表

爲何不用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！實際狀況了？
  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

普通機械磁盤機器
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併發線程	124 tps	122 tps
10併發線程	123 tps	121 tps
20併發線程	125 tps	104 tps
30併發線程	127 tps	67 tps
40併發線程	127 tps	33 tps

• 可見myisam隨着併發線程數的增長，replace into tps保持不變，緣由是myisam是表鎖，同一時刻，該表只能寫或者只能讀
• innodb表隨着併發數的上升，insert..on duplicate tps不升反降，行鎖以前的爭用變大了 形成鎖等待
• 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個併發線程時可能會出現死鎖（RC隔離級別也是），死鎖詳細見最後
爲何sysbench40 併發線程測試沒有出現過死鎖？難道sysbench併發線程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，無論併發線程數多少，生成序列速度是穩定的，但myisam表存在缺陷問題
• innodb表 inert on duplicate 生成序列適合併發線程數少狀況，併發線程數多會出現死鎖 生成序列速度降低狀況
• 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腳本
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()
end