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Alex Hales
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Alex HalesTeacher
Asked: July 15, 20222022-07-15T00:45:36+00:00 2022-07-15T00:45:36+00:00In: Database, innodb, MySQL

database – How to shrink/purge ibdata1 file in MySQL

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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

https://dev.mysql.com/doc/refman/5.6/en/innodb-file-per-table-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.

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