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How to shrink/purge ibdata1 file in MySQL (6)

I am using MySQL in localhost as a "query tool" for performing statistics in R, that is, everytime I run a R script, I create a new database (A), create a new table (B), import the data into B, submit a query to get what I need, and then I drop B and drop A.

It's working fine for me, but I realize that the ibdata file size is increasing rapidly, I stored nothing in MySQL, but the ibdata1 file already exceeded 100 MB.

I am using more or less default MySQL setting for the setup, is there a way for I can automatically shrink/purge the ibdata1 file after a fixed period of time?


If you use the InnoDB storage engine for (some of) your MySQL tables, you’ve probably already came across a problem with its default configuration. As you may have noticed in your MySQL’s data directory (in Debian/Ubuntu – /var/lib/mysql) lies a file called ‘ibdata1′. It holds almost all the InnoDB data (it’s not a transaction log) of the MySQL instance and could get quite big. By default this file has a initial size of 10Mb and it automatically extends. Unfortunately, by design InnoDB data files cannot be shrinked. That’s why DELETEs, TRUNCATEs, DROPs, etc. will not reclaim the space used by the file.

I think you can find good explanation and solution there :

http://vdachev.net/2007/02/22/mysql-reducing-ibdata1/


Adding to John P's answer,

For a linux system, steps 1-6 can be accomplished with these commands:

  1. mysqldump -u [username] -p[root_password] [database_name] > dumpfilename.sql
  2. DROP DATABASE [database_name];
  3. sudo /etc/init.d/mysqld stop
  4. sudo rm /var/lib/mysql/ibdata1
    sudo rm /var/lib/mysql/ib_logfile (and delete any other ib_logfile's that may be named ib_logfile0, ib_logfile1 etc...)
  5. sudo /etc/init.d/mysqld start
  6. create database [database_name];
  7. mysql -u [username]-p[root_password] [database_name] < dumpfilename.sql

Warning: these instructions will cause you to lose other databases if you have other databases on this mysql instance. Make sure that steps 1,2 and 6,7 are modified to cover all databases you wish to keep.


If your goal is to monitor MySQL free space and you can't stop MySQL to shrink your ibdata file, then get it through table status commands. Example:

MySQL > 5.1.24:

mysqlshow --status myInnodbDatabase myTable | awk '{print $20}'

MySQL < 5.1.24:

mysqlshow --status myInnodbDatabase myTable | awk '{print $35}'

Then compare this value to your ibdata file:

du -b ibdata1

Source: http://dev.mysql.com/doc/refman/5.1/en/show-table-status.html


In a new version of mysql-server recipes above will crush "mysql" database. In old version it works. In new some tables switches to table type INNODB, and by doing so you will damage them. The easiest way is to dump all you databases, uninstall mysql-server, add in remained my.cnf:

[mysqld]
innodb_file_per_table=1


erase all in /var/lib/mysql
install mysql-server
restore users and databases

That ibdata1 isn't shrinking is a particularly annoying feature of MySQL. The ibdata1 file can't actually be shrunk unless you delete all databases, remove the files and reload a dump.

But you can configure MySQL so that each table, including its indexes, is stored as a separate file. In that way ibdata1 will not grow as large. According to Bill Karwin's comment this is enabled by default as of version 5.6.6 of MySQL.

It was a while ago I did this. However, to setup your server to use separate files for each table you need to change my.cnf in order to enable this:

[mysqld]
innodb_file_per_table=1

http://dev.mysql.com/doc/refman/5.5/en/innodb-multiple-tablespaces.html

As you want to reclaim the space from ibdata1 you actually have to delete the file:

  1. Do a mysqldump of all databases, procedures, triggers etc except the mysql and performance_schema databases
  2. Drop all databases except the above 2 databases
  3. Stop mysql
  4. Delete ibdata1 and ib_log files
  5. Start mysql
  6. Restore from dump

When you start MySQL in step 5 the ibdata1 and ib_log files will be recreated.

Now you're fit to go. When you create a new database for analysis, the tables will be located in separate ibd* files, not in ibdata1. As you usually drop the database soon after, the ibd* files will be deleted.

http://dev.mysql.com/doc/refman/5.1/en/drop-database.html

You have probably seen this:
http://bugs.mysql.com/bug.php?id=1341

By using the command ALTER TABLE <tablename> ENGINE=innodb or OPTIMIZE TABLE <tablename> one can extract data and index pages from ibdata1 to separate files. However, ibdata1 will not shrink unless you do the steps above.

Regarding the information_schema, that is not necessary nor possible to drop. It is in fact just a bunch of read-only views, not tables. And there are no files associated with the them, not even a database directory. The informations_schema is using the memory db-engine and is dropped and regenerated upon stop/restart of mysqld. See https://dev.mysql.com/doc/refman/5.7/en/information-schema.html.


When you delete innodb tables, MySQL does not free the space inside the ibdata file, that's why it keeps growing. These files hardly ever shrink.

How to shrink an existing ibdata file:

http://dev.mysql.com/doc/refman/5.5/en/innodb-resize-system-tablespace.html

You can script this and schedule the script to run after a fixed period of time, but for the setup described above it seems that multiple tablespaces are an easier solution.

If you use the configuration option innodb_file_per_table, you create multiple tablespaces. That is, MySQL creates separate files for each table instead of one shared file. These separate files a stored in the directory of the database, and they are deleted when you delete this database. This should remove the need to shrink/purge ibdata files in your case.

More information about multiple tablespaces:

http://dev.mysql.com/doc/refman/5.5/en/innodb-multiple-tablespaces.html





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