MySql - changing innodb_file_per_table for a live db
There is really only one way to pull this off. You will have to export the data using mysqldumps, drop all databases, shutdown mysqld, delete ib_logfile0, delete ib_logfile1, delete ibdata1, add innodb_file_per_table under the [mysqld] heading, start mysql.

I posted this answer in StackOverflow back in October 2010

Here are the steps listed vertically:

Step 01) MySQLDump all databases into a SQL text file (call it SQLData.sql)

Step 02) Drop all databases (except mysql schema)

Step 03) Shutdown mysql

CAVEAT: To totally clean out uncommitted transactions from the InnoDB Files, run this

mysql -uroot -p... -Ae"SET GLOBAL innodb_fast_shutdown = 0;"
service mysql stop


Step 04) Add the following lines to /etc/my.cnf

[mysqld]
innodb_file_per_table
innodb_flush_method=O_DIRECT
innodb_log_file_size=1G
innodb_buffer_pool_size=4G


Sidenote: Whatever your set for innodb_buffer_pool_size, make sure innodb_log_file_size is 25% of innodb_buffer_pool_size.

Step 05) Delete ibdata1, ib_logfile0 and ib_logfile1

At this point, there should only be the mysql schema in /var/lib/mysql

Step 06) Restart mysql

This will recreate ibdata1 at 10MB, ib_logfile0 and ib_logfile1 at 1G each

Step 07) Reload SQLData.sql into mysql

ibdata1 will grow but only contain table metadata

Each InnoDB table will exist outside of ibdata1

Suppose you have an InnoDB table named mydb.mytable. If you go into /var/lib/mysql/mydb, you will see two files representing the table


mytable.frm (Storage Engine Header)
mytable.ibd (Home of Table Data and Table Indexes for mydb.mytable)


ibdata1 will never contain InnoDB data and Indexes anymore.

With the innodb_file_per_table option in /etc/my.cnf, you can run OPTIMIZE TABLE mydb.mytable and the file /var/lib/mysql/mydb/mytable.ibd will actually shrink.

I have done this many times in my career as a MySQL DBA

In fact, the first time I did this, I collapsed a 50GB ibdata1 file into 500MB.

Give it a try. If you have further questions on this, email me. Trust me. This will work in the short term and over the long haul. !!!

There is an alternative that will extract the InnoDB table without shrinking ibdata1.

Step 01) Add the following lines to /etc/my.cnf

[mysqld]
innodb_file_per_table
innodb_flush_method=O_DIRECT
innodb_log_file_size=1G
innodb_buffer_pool_size=4G


Step 02) service mysql restart

Step 03) To extract a single InnoDB table called mydb.mytable, do this:

ALTER TABLE mydb.mytable ENGINE=InnoDB;


This will create one file pleus keep the original structure file


/var/lib/mysql/mydb/mytable.frm
/var/lib/mysql/mydb/mytable.ibd


You can do this for every InnoDB table. Unfortunately, ibdata1 will stay 150GB.