TDSQL FOR MYSQL 内部的自增例介绍

TDSQL 自增列：

Mysql 的innodb中常用自增列来存储某表的唯一ID例，每次mysqld启动后首次打开这个表时，把这个索引的最大值取出来作为自增例的起始值，并且存储在内存中，然后mysqld运行期间妈可维护和使用这个自增例值。

TDSQL 作为高度兼容MYSQL语法的数据库，自然也是有全局唯一自增列这一功能。关键字auto_increment，即支持一个全局的自增字段，auto_increment 可以保证该表某个字段全局唯一，但不保证单调递增。TDSQL自增例的值是保存在Zk组件中的，当Proxy启动后，会从ZK中取一个号段，每个Proxy 都是从ZK中取的唯一号段，所以它能保证唯一；但是由于它取的是号段，当SQL选择不同的Proxy时对SQL操作时，它不能保证连续，如果Proxy 挂掉，在恢复的时候会重新向ZK去请求一个号段。这样的好处，不用频繁的去ZK中取，避免了资源竞争，有利于性能的提长。

#创建自增例的表，

这种设计方式实现了分布式环境下的自增属性全局唯一。每个Proxy缓存一定数量的值，并且增加单独线程负责向ZK申请值，使得性能影响降到最低，同时具有容灾特性，即使Proxy挂了或者重启，都能保证全局唯一。但是缺点是：多个Proxy一起使用的时候，只能保证全局唯一，不能保证单调递增。

下面我们来验证自增例：

#1.创建一张带有自增例的表

MySQL [–c]> mysql -uhuyi -phuyi -h10.85.10.51 -P15002 –c
MySQL [–c]> create database huyidb ;
MySQL [–c]> create table huyidb.test4 ( a int auto_increment , b int , c char(20),primary key (a),unique key u_2(a,c) ) shardkey=a;
Query OK, 0 rows affected (0.75 sec)

#2.在Porxy1 插入5条数据

mysql -uhuyi -phuyi -h10.85.10.51 -P15002 –c
insert into huyidb.test4 ( a,b, c) values (0,10, 'huyi01') ;
insert into huyidb.test4 ( a,b, c) values (0,20, 'huyi02') ;
insert into huyidb.test4 ( a,b, c) values (0,30, 'huyi03') ;
insert into huyidb.test4 ( a,b, c) values (0,40, 'huyi04') ;
insert into huyidb.test4 ( a,b, c) values (0,50, 'huyi05') ;
select last_insert_id()  ;

MySQL [–c]> insert into huyidb.test4 ( a,b, c) values (0,10, 'huyi01') ;
Query OK, 1 row affected (0.01 sec)
 
MySQL [–c]> insert into huyidb.test4 ( a,b, c) values (0,20, 'huyi02') ;
Query OK, 1 row affected (0.01 sec)

MySQL [–c]> insert into huyidb.test4 ( a,b, c) values (0,30, 'huyi03') ;
Query OK, 1 row affected (0.01 sec)

MySQL [–c]> insert into huyidb.test4 ( a,b, c) values (0,40, 'huyi04') ;
Query OK, 1 row affected (0.00 sec)

MySQL [–c]> insert into huyidb.test4 ( a,b, c) values (0,50, 'huyi05') ;
Query OK, 1 row affected (0.00 sec)

#3.当前最大自增例的值是5

MySQL [–c]>     select last_insert_id()  ;
+------------------+
| last_insert_id() |
+------------------+
| 5                |
+------------------+
1 row in set (0.00 sec)

#4.在Porxy2插入5条数据

mysql -uhuyi -phuyi -h10.85.10.52 -P15002 –c
insert into huyidb.test4 ( a,b, c) values (0,12, 'huyi21') ;
insert into huyidb.test4 ( a,b, c) values (0,22, 'huyi22') ;
insert into huyidb.test4 ( a,b, c) values (0,32, 'huyi23') ;
insert into huyidb.test4 ( a,b, c) values (0,42, 'huyi24') ;
insert into huyidb.test4 ( a,b, c) values (0,55, 'huyi25') ;
select last_insert_id()  ;

MySQL [–c]> insert into huyidb.test4 ( a,b, c) values (0,12, 'huyi21') ;
insert into huyidb.test4 ( a,b, c) values (0,22, 'huyi22') ;
Query OK, 1 row affected (0.01 sec)

MySQL [–c]> insert into huyidb.test4 ( a,b, c) values (0,22, 'huyi22') ;
Query OK, 1 row affected (0.00 sec)

MySQL [–c]> insert into huyidb.test4 ( a,b, c) values (0,32, 'huyi23') ;
Query OK, 1 row affected (0.01 sec)

MySQL [–c]> insert into huyidb.test4 ( a,b, c) values (0,42, 'huyi24') ;
Query OK, 1 row affected (0.01 sec)

MySQL [–c]> insert into huyidb.test4 ( a,b, c) values (0,55, 'huyi25') ;
Query OK, 1 row affected (0.00 sec)

#5.当前最大自增例是2005,说明自增例是不保证连续的

MySQL [–c]> select last_insert_id()  ; 
+------------------+
| last_insert_id() |
+------------------+
| 2005             |
+------------------+

1 row in set (0.00 sec)

#6.模拟Proxy1挂掉

ps -ef |grep gateway |grep 15002
ps -ef |grep gateway |grep 15002 | grep -v 'grep'| awk '{print $2}' | xargs kill -9
ps -ef |grep gateway |grep 15002

#7.待Proxy1重新挂起后，再次插入5条数据

mysql -uhuyi  -phuyi -h10.85.10.51 -P15002 -c
insert into huyidb.test4 ( a,b, c) values (0,13, 'huyi31') ;
insert into huyidb.test4 ( a,b, c) values (0,23, 'huyi32') ;
insert into huyidb.test4 ( a,b, c) values (0,33, 'huyi33') ;
insert into huyidb.test4 ( a,b, c) values (0,43, 'huyi34') ;
insert into huyidb.test4 ( a,b, c) values (0,53, 'huyi35') ;


MySQL [(none)]> insert into huyidb.test4 ( a,b, c) values (0,13, 'huyi31') ;
Query OK, 1 row affected (0.00 sec)

MySQL [(none)]> insert into huyidb.test4 ( a,b, c) values (0,23, 'huyi32') ;
Query OK, 1 row affected (0.01 sec)

MySQL [(none)]> insert into huyidb.test4 ( a,b, c) values (0,33, 'huyi33') ;
Query OK, 1 row affected (0.01 sec)

MySQL [(none)]> insert into huyidb.test4 ( a,b, c) values (0,43, 'huyi34') ;
Query OK, 1 row affected (0.01 sec)

MySQL [(none)]> insert into huyidb.test4 ( a,b, c) values (0,53, 'huyi35') ;
Query OK, 1 row affected (0.00 sec)

#8.当前的自增例跳到5005，也就是说在proxy网关故障恢复后，会重新从zk中获取一段唯一

MySQL [(none)]>  select last_insert_id()  ;   
+------------------+
| last_insert_id() |
+------------------+
| 5005             |
+------------------+
1 row in set (0.00 sec)

MySQL [(none)]>    select * from    huyidb.test4 ;
+------+------+--------+
| a    | b    | c      |
+------+------+--------+
|    1 |   10 | huyi01 |
| 2005 |   55 | huyi25 |
| 5002 |   23 | huyi32 |
| 2004 |   42 | huyi24 |
| 2002 |   22 | huyi22 |
| 2001 |   12 | huyi21 |
|    2 |   20 | huyi02 |
| 5004 |   43 | huyi34 |
|    5 |   50 | huyi05 |
|    3 |   30 | huyi03 |
| 2003 |   32 | huyi23 |
| 5005 |   53 | huyi35 |
| 5003 |   33 | huyi33 |
| 5001 |   13 | huyi31 |
|    4 |   40 | huyi04 |
+------+------+--------+

15 rows in set (0.00 sec);

从网关日志中可以看出，在ZK中获取了相关的路由信息，shardkey , 以及自己增例等信息。

more  /data/tdsql_run/15002/gateway/log/sys_instance_15002.2020-12-29.0/data/tdsql_run/15002/gateway/log/
main/proxy-zookeeper.c:275:get_new_id,tid:0x7f3c9d3f5700,con:(nil),get_new_id current:0,old_value:7000,step:1000,db_table:huyidb.test4
main/proxy-zookeeper.c:139:deal_one_path,tid:0x7f3c9f3f7700,con:(nil),deal_one_path :/tdsqlzk/group_1609208018_42/sequenceids/sequenceid@huyidb.test4/alter_seqid,event:3
main/proxy-zookeeper.c:287:get_new_id,tid:0x7f3c9d3f5700,con:(nil),get_new_id,set_path node:/tdsqlzk/group_1609208018_42/sequenceids/sequenceid@huyidb.test4/current_id,new_value:8000,return :7000,
main/auto_inc.h:109:get_new_id,tid:0x7f3c9d3f5700,con:(nil),get_new_id:7000 from zk,can use (7000,8000] for db_table:huyidb.test4
main/proxy-zookeeper.c:170:deal_one_path,tid:0x7f3c9f3f7700,con:(nil),in deal_one_path:/tdsqlzk/group_1609208018_42/sequenceids/sequenceid@huyidb.test4/alter_seqid,got a new value:0 for db_table:h
main/proxy-zookeeper.c:139:deal_one_path,tid:0x7f3c9f3f7700,con:(nil),deal_one_path :/tdsqlzk/group_1609208018_42/sequenceids/sequenceid@huyidb.test4/current_id,event:3
main/proxy-zookeeper.c:275:get_new_id,tid:0x7f3c9d3f5700,con:(nil),get_new_id current:0,old_value:5000,step:1000,db_table:huyidb.test5
main/proxy-zookeeper.c:139:deal_one_path,tid:0x7f3c9f3f7700,con:(nil),deal_one_path :/tdsqlzk/group_1609208018_42/sequenceids/sequenceid@huyidb.test5/alter_seqid,event:3
main/proxy-zookeeper.c:287:get_new_id,tid:0x7f3c9d3f5700,con:(nil),get_new_id,set_path node:/tdsqlzk/group_1609208018_42/sequenceids/sequenceid@huyidb.test5/current_id,new_value:6000,return :5000,
main/auto_inc.h:109:get_new_id,tid:0x7f3c9d3f5700,con:(nil),get_new_id:5000 from zk,can use (5000,6000] for db_table:huyidb.test5
main/proxy-zookeeper.c:170:deal_one_path,tid:0x7f3c9f3f7700,con:(nil),in deal_one_path:/tdsqlzk/group_1609208018_42/sequenceids/sequenceid@huyidb.test5/alter_seqid,got a new value:0 for db_table:h
main/proxy-zookeeper.c:139:deal_one_path,tid:0x7f3c9f3f7700,con:(nil),deal_one_path :/tdsqlzk/group_1609208018_42/sequenceids/sequenceid@huyidb.test5/current_id,event:3
main/proxy-zookeeper.c:139:deal_one_path,tid:0x7f3c9f3f7700,con:(nil),deal_one_path :/tdsqlzk/group_1609208018_42/groupdcn,event:3
main/proxy-extend.cpp:457:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread version is not equal to gloabl,so update version to:6,after update:
main/proxy-extend.cpp:460:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread update groupstatus to :0
main/proxy-extend.cpp:463:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route set_range set_name:set_1609208277_1,range:0-31
main/proxy-extend.cpp:463:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route set_range set_name:set_1609208653_3,range:32-63
main/proxy-extend.cpp:465:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route set_slice set_name:set_1609208277_1,slice:0
main/proxy-extend.cpp:465:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route set_slice set_name:set_1609208653_3,slice:0
main/proxy-extend.cpp:468:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route dbtable_shardkey  dbtable:huyidb.test4,shardkey:a
main/proxy-extend.cpp:468:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route dbtable_shardkey  dbtable:huyidb.test5,shardkey:a
main/proxy-extend.cpp:491:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route dbtable_auto_inc dbtable:huyidb.test4,auto_inc:a
main/proxy-extend.cpp:491:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route dbtable_auto_inc dbtable:huyidb.test5,auto_inc:a
main/proxy-extend.cpp:494:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route dbtable_auto_inc_type dbtable:huyidb.test4,auto_inc_type:0
main/proxy-extend.cpp:494:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route dbtable_auto_inc_type dbtable:huyidb.test5,auto_inc_type:0
main/proxy-extend.cpp:496:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route dbtable_auto_inc_step dbtable:huyidb.test4,auto_inc_step:1000
main/proxy-extend.cpp:496:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread route dbtable_auto_inc_step dbtable:huyidb.test5,auto_inc_step:1000
main/proxy-extend.cpp:512:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread sets master set_name:set_1609208277_1,ip:10.85.10.51:4005
main/proxy-extend.cpp:512:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread sets master set_name:set_1609208653_3,ip:10.85.10.51:4006
main/proxy-extend.cpp:514:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread sets master set_name:set_1609208277_1,status:0
main/proxy-extend.cpp:514:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread sets master set_name:set_1609208653_3,status:0
main/proxy-extend.cpp:516:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread sets slave set_name:set_1609208277_1,ip:10.85.10.52:4005@1@IDC_CQ_YB_9527_02@0,10.85.10.53:4005@1@IDC_CQ_YB_9527_03
main/proxy-extend.cpp:516:print_backend_info,tid:0x7f3ce6fff700,con:(nil),thread sets slave set_name:set_1609208653_3,ip:10.85.10.52:4006@1@IDC_CQ_YB_9527_02@0,10.85.10.53:4006@1@IDC_CQ_YB_9527_03

那自增例里面的值，多个表可以混用么？我们创建第二个自增例的表来确认一下。

create table huyidb.test5 ( a int auto_increment , b int , c char(20),primary key (a),unique key u_2(a,c) ) shardkey=a;
mysql -uhuyi  -phuyi -h10.85.10.51 -P15002 -c

MySQL [(none)]>  insert into huyidb.test5 ( a,b, c) values (0,55, 'huyi55') ;
Query OK, 1 row affected (0.01 sec)

#从结果可以看出，每个表的自增例都是独立的，表与表之间的自增例不能混用

MySQL [(none)]> select last_insert_id()  ;
| last_insert_id() |
+------------------+
| 1                |
+------------------+

1 row in set (0.00 sec)

#同时不能在一个表上创建2个自增例

MySQL [(none)]> create table huyidb.test6 ( a int auto_increment , b int auto_increment, c char(20),primary key (a),unique key u_2(a,c) ) shardkey=a;
ERROR 688 (HY000): Proxy ERROR:Complex sql can not used to create shard tables

我们从ZK中查看是如何分配的,我们以test5 表为例;

首先我们查看zk中当前最大的自增例的值是5000

 [zk: localhost:2181(CONNECTED) 8] get /tdsqlzk/group_1609208018_42/sequenceids/sequenceid@huyidb.test5/current_id
5000
cZxid = 0x359bf
ctime = Tue Dec 29 10:37:27 CST 2020
mZxid = 0x35dfb
mtime = Tue Dec 29 10:38:57 CST 2020
pZxid = 0x359bf
cversion = 0
dataVersion = 5
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 4
numChildren = 0

2.我们在次kill proxy进程，模拟故障，待网关恢复后，我发现新插入的值为5001

[root@tdsql1 bin]# mysql -uhuyi  -phuyi -h10.85.10.51 -P15002 -c
Welcome to the MariaDB monitor.  Commands end with ; or g.
Your MySQL connection id is 3347
Server version: 5.7.17-11-V2.0R540D002-20191226-1152-log Source distribution
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.

MySQL [(none)]>  insert into huyidb.test5 ( a,b, c) values (0,55, 'huyi55') ;
Query OK, 1 row affected (0.00 sec)

MySQL [(none)]> select last_insert_id()  ;
+------------------+
| last_insert_id() |
+------------------+
| 5001             |
+------------------+
1 row in set (0.00 sec)

3.同时我要在zk中查看当前最大的值为6000，即验证了我们最初图中所说，proxy是从zk中取一段自增例缓存到proxy中。

[zk: localhost:2181(CONNECTED) 9] get /tdsqlzk/group_1609208018_42/sequenceids/sequenceid@huyidb.test5/current_id
6000
cZxid = 0x359bf
ctime = Tue Dec 29 10:37:27 CST 2020
mZxid = 0x371d9
mtime = Tue Dec 29 10:45:55 CST 2020
pZxid = 0x359bf
cversion = 0
dataVersion = 6
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 4
numChildren = 0

目前 select last_insert_id() 只能跟 shard 表和广播表的自增字段一起使用，不支持 noshard 表。

自增例的缺陷：

每个表只能有一个自增列，并且这个自增列必须是一个索引的第一列。
同时，一个自增序列无法给多个表使用。

3.无法独立引用(refer to)一个表的自增列的当前值（last_insert_id无法指定某个表）