How to Use pt-online-schema-change to change the primary key of a MySQL table, ptonlinechangeschema

How to Use pt-online-schema-change to change the primary key of a MySQL table, ptonlinechangeschema

When the service runs for a period of time and finds that the original primary key settings are not reasonable, you want to change the primary key. This kind of requirement is quite large in actual production.

Next, let's take a look at how pt-online-schema-change solves such problems.

 

First, create a test table

Create table t2 (c1 int primary key, c2 int );

 

Construct Test Data

delimiter //create procedure p1()begin  declare v1 int default 1;  set autocommit=0;  while v1 <=100000 do    insert into test.t2(c1,c2) values(v1,v1+100);    set v1=v1+1;    if v1%1000 =0 then      commit;    end if;  end while;end //delimiter ;call p1;

 

Next, Use pt-online-schema-change to change the primary key of table t2.

1. Add the unique key to the c1 Column

# pt-online-schema-change --execute --alter "modify c1 int unique key"  --print D=test,t=t2 

The table structure of table t2 is as follows:

mysql> show create table t2\G*************************** 1. row ***************************       Table: t2Create Table: CREATE TABLE `t2` (  `c1` int(11) NOT NULL DEFAULT '0',  `c2` int(11) DEFAULT NULL,  PRIMARY KEY (`c1`),  UNIQUE KEY `c1` (`c1`)) ENGINE=InnoDB DEFAULT CHARSET=utf81 row in set (0.03 sec)

 

2. Delete the primary key of column c1

# Pt-online-schema-change -- execute -- alter "drop primary key" -- no-check-alter -- print D = test, t = t2

Note: The -- no-check-alter option must be added to delete the primary key.

The table structure of table t2 is as follows:

mysql> show create table t2\G*************************** 1. row ***************************       Table: t2Create Table: CREATE TABLE `t2` (  `c1` int(11) NOT NULL DEFAULT '0',  `c2` int(11) DEFAULT NULL,  UNIQUE KEY `c1` (`c1`)) ENGINE=InnoDB DEFAULT CHARSET=utf81 row in set (0.05 sec)

 

3. Add the primary key of the c2 Column

# Pt-online-schema-change -- execute -- alter "modify c2 int primary key" -- print D = test, t = t2

The table structure of table t2 is as follows:

mysql> show create table t2\G*************************** 1. row ***************************       Table: t2Create Table: CREATE TABLE `t2` (  `c1` int(11) NOT NULL DEFAULT '0',  `c2` int(11) NOT NULL,  PRIMARY KEY (`c2`),  UNIQUE KEY `c1` (`c1`)) ENGINE=InnoDB DEFAULT CHARSET=utf81 row in set (0.02 sec)

 

4. Delete the unique key of column c1

# Pt-online-schema-change -- execute -- alter "drop key c1" -- print D = test, t = t2

The primary key of t2 is changed.

mysql> show create table t2\G*************************** 1. row ***************************       Table: t2Create Table: CREATE TABLE `t2` (  `c1` int(11) NOT NULL DEFAULT '0',  `c2` int(11) NOT NULL,  PRIMARY KEY (`c2`)) ENGINE=InnoDB DEFAULT CHARSET=utf81 row in set (0.02 sec)