MySQL: reducing ibdata file size for MyISAM tables

Question

My Question is actually very similar to this one and also includes a good answer for a case with InnoDB Engine tables:

https://dba.stackexchange.com/questions/8982/i

Answer 1

ibdata1 and MyISAM are mutually exclusive.

First thing you should do is count how many tables use both storage engines:

SELECT COUNT(1) EngineCount,engine
FROM information_schema.tables
WHERE table_schema NOT IN ('information_schema','performance_schema','mysql')
GROUP BY engine;

If SOME tables are InnoDB:

Perform my CleanUp of InnoDB

• Howto: Clean a mysql InnoDB storage engine?
• https://dba.stackexchange.com/questions/8982/is-there-any-best-way-to-reduce-the-size-of-ibdata-in-mysql/8983#8983

If you have only MyISAM tables and no InnoDB tables:

First, eliminate any traces of InnoDB Do the following:

STEP01) Add this to my.cnf

[mysqld]
skip-innodb

STEP02) service mysql restart

STEP03) rm -f /var/lib/mysql/ibdata1 /var/lib/mysql/ib_logfile*

After these steps, you can perform a Compression of Each MyISAM tables like this:

For the table mydb.mytable that is MyISAM, just run one of the following:

• OPTIMIZE TABLE mydb.mytable;
• ALTER TABLE mydb.mytable ENGINE=MyISAM; ANALYZE TABLE mydb.mytable;

If you want to defrag all your MyISAM tables, here is a shell script to do so...

MYSQL_USER=root
MYSQL_PASS=rootpassword
MYSQL_CONN="-u${MYSQL_USER} -p${MYSQL_PASS}"
SQL="SELECT CONCAT('OPTIMIZE TABLE ',table_schema,'.',table_name,';') "
SQL="${SQL} FROM information_schema.tables "
SQL="${SQL} WHERE engine='MyISAM' AND table_schema NOT IN "
SQL="${SQL} ('information_schema','performance_schema','mysql')"
mysql ${MYSQL_CONN} -ANe"${SQL}" > GlobalMyISAMOptmizeTable.sql
less GlobalMyISAMOptmizeTable.sql

Once you trust the script visually, just run it

mysql ${MYSQL_CONN} < GlobalMyISAMOptmizeTable.sql

Give it a Try !!!

UPDATE 2012-07-25 09:52 EDT

I would like to clarify one of my suggestions for compression of MyISAM

I said earlier

• OPTIMIZE TABLE mydb.mytable;
• ALTER TABLE mydb.mytable ENGINE=MyISAM; ANALYZE TABLE mydb.mytable;

These commands are mechanically identical. OPTIMIZE TABLE performs a defrag of the MyISAM table and then runs ANALYZE TABLE to compute fresh index statistics.

Mechanically speaking, this is what ALTER TABLE mydb.mytable ENGINE=MyISAM; does:

CREATE TABLE mydb.mytabletmp LIKE mydb.mytable;
INSERT INTO mydb.mytabletmp SELECT * FROM mydb.mytable;
ALTER TABLE mydb.mytable RENAME mydb.mytablezap;
ALTER TABLE mydb.mytabletmp RENAME mydb.mytable;
DROP TABLE mydb.mytablezap;

Answer 2

As mentioned MyISAM shouldn't be using ibdata. What are your innodb settings in your my.cnf, or in the MySQL shell type:

    SHOW VARIABLES LIKE "%innodb%";

Are these variables set?

    innodb_data_home_dir
    innodb_data_file_path

If you are not using INNODB at all you should be able to safely remove the ibdata and ib_logfile(s) and restart MySQL. Normally though removing these without dropping the tables first will cause issues. See How to shrink/purge ibdata1 file in MySQL

If you do have a MyISAM table over 5Gigs, it's recommended that you use INNODB anyway. (Anything over 4 Gigs). To troubleshoot you could try and add

    skip-innodb 

in the my.cnf if you are not using INNODB at all.