Mysql – How to convert a MyISAM .sql dump into InnoDB

The following exerpt came out of the book "High Performance MySQL, Second Edition".

This is an excellent book and I would recommend it to anyone.

The short answer is:

With your table size and conditions, no matter what method you choose, I think you're potentially in for a long wait.

Table Conversions

There are several ways to convert a table from one storage engine to another, each with advantages and disadvantages.

ALTER TABLE

mysql> ALTER TABLE mytable ENGINE = Falcon;

This syntax works for all storage engines, but there’s a catch: it can take a lot of time. MySQL will perform a row-by-row copy of your old table into a new table. During that time, you’ll probably be using all of the server’s disk I/O capacity, and the original table will be read-locked while the conversion runs.

Dump and import

To gain more control over the conversion process, you might choose to first dump the table to a text file using the mysqldump utility. Once you’ve dumped the table, you can simply edit the dump file to adjust the CREATE TABLE statement it contains. Be sure to change the table name as well as its type, because you can’t have two tables with the same name in the same database even if they are of different types—and mysqldump defaults to writing a DROP TABLE command before the CREATE TABLE, so you might lose your data if you are not careful!

CREATE and SELECT

The third conversion technique is a compromise between the first mechanism’s speed and the safety of the second. Rather than dumping the entire table or converting it all at once, create the new table and use MySQL’s INSERT ... SELECT syntax to populate it, as follows:

mysql> CREATE TABLE innodb_table LIKE myisam_table;
mysql> ALTER TABLE innodb_table ENGINE=InnoDB;
mysql> INSERT INTO innodb_table SELECT * FROM myisam_table;

That works well if you don’t have much data, but if you do, it’s often more efficient to populate the table incrementally, committing the transaction between each chunk so the undo logs don’t grow huge. Assuming that id is the primary key, run this query repeatedly (using larger values of x and y each time) until you’ve copied all the data to the new table:

mysql> START TRANSACTION;
mysql> INSERT INTO innodb_table SELECT * FROM myisam_table
-> WHERE id BETWEEN x AND y;
mysql> COMMIT;

After doing so, you’ll be left with the original table, which you can drop when you’re done with it, and the new table, which is now fully populated. Be careful to lock the original table if needed to prevent getting an inconsistent copy of the data!

ISAM = Indexed Sequential Access Method and is essentially a flat file (for those DBAs who can remember, think Btrieve, or B-Tree). It's a very old technology - but don't let that put you off using it. Because it's a flat file (more on that later), it is not relational, and thus is not an RDBMS, and thus is more appropriate in some situations.

InnoDB is the full RDBMS like you are most likely familiar with. MyISAM can appear to be relational through another layer added on top that maintains your links, logic and referential integrity.

ISAM is brilliant if you have a LOT of records (like, 20 million), and the records are mostly stand-alone (i.e. you don't need to do lots of links to retrieve associated data). It relies VERY heavilly on indexes and if you don't have the right index, be prepared for very very long query times. Case in point: We had a Btrieve ISAM table with 20M+ records and to do a retrieve and filter data based on an accurate index was almost instant. Using the wrong index was literally 15 minutes.

InnoDB is great for if you have a lot of relational links. Table A references a field in Table B, which references Table C and D. InnoDB can fetch these records using all sorts of nice joining methods (hash joins, etc), whereas an ISAM database would have to run multiple sub-queries for every single row and match the records manually.

You will really have to do a course in databases if you want much more detail than that!