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Displaying posts with tag: tablespace (reset)
Data Organization in InnoDB


This article will explain how the data is organized in InnoDB storage engine. First we will look at the various files that are created by InnoDB, then we look at the logical data organization like tablespaces, pages, segments and extents. We will explore each of them in some detail and discuss about their relationship with each other. At the end of this article, the reader will have a high level view of the data layout within the InnoDB storage engine.

The Files

MySQL will store all data within the data directory. The data directory can be specified using the command line option –data-dir or in the configuration file as datadir. Refer to the Server Command Options for complete details.

By default, when InnoDB is initialized, it creates 3 important files in the data directory – ibdata1, ib_logfile0 and …

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What a Hosting Provider did Today

I found Dennis the Menace, he now has a job as system administrator for a hosting company. Scenario: client has a problem with a server becoming unavailable (cause unknown) and has it restarted. MySQL had some page corruption in the InnoDB tablespace.

The hosting provider, being really helpful, goes in as root and first deletes ib_logfile* then ib* in /var/lib/mysql. He later says “I am sorry if I deleted it. I thought I deleted the log only. Sorry again.”  Now this may appear nice, but people who know what they’re doing with MySQL will realise that deleting the iblogfiles actually destroys data also. MySQL of course screams loudly that while it has FRM files it can’t find the tables. No kidding!

Then, while he’s been told to not touch anything any more, and I’m trying to see if I can recover the deleted files on ext3 filesystem (yes there are tools for that), he goes in again and puts an ibdata1 file back. No, …

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InnoDB's tablespace ids and Partitions

There are times when what you have is a partially running database and a bunch of backup innodb tablespace files (the .ibd files). If you're using innodb_file_per_table, then you have a separate .ibd file for each InnoDB table.

Now, you have your running database with a bunch of tables, and you want to replace some of them with the backup .ibd files. According to the MySQL docs, you'd do this:

  1. ALTER TABLE foo DISCARD TABLESPACE; (this deletes the current .ibd file)
  2. copy the old .ibd file into your database directory

Assuming your .ibd file was from the same database and you did not drop the table and recreate it sometime between when you made the backup .ibd and now, this should work. Except... if …

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Variable's Day Out #10: innodb_file_per_table


Applicable To InnoDB
Server Startup Option --innodb-file-per-table
Scope Global
Dynamic General InnoDB Engine: No
InnoDB plug-in: Yes
Possible Values Enable|Disable Flag
Default Value Disabled
Category Maintenance


This variable if enabled, makes InnoDB to create a separate .ibd file for storing indexes and data. Setting this variable makes it easy to manage disks with huge tables. Having …

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Tablespaces in MySQL, Oracle and Postgres

If you are not familiar with tablespaces you may be wondering what the big deal about them is. Tablespaces are a logical addition to a database that helps maintenance, and potentially, can improve performance.

In Oracle and MySQL, a tablespace is a logical unit meant to store segments (i.e. tables and indexes). In Postgres, a tablespace is a physical unit. It is a symbolic link to a directory. Postgres does not allow tablespaces on operating systems that do not support symbolic links (such as windows).

The data file is the actual physical storage mechanism in Oracle and MySQL. Postgres stores tables in individual files. Postgres support of tablespaces is minimal. In MySQL and Oracle, performance can be improved by a more granular spread of data across disks. Ease of maintenance is maintained due to the logical grouping of tablespaces.

Oracle syntax for creating a tablespace is much the same as MySQL …

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Showing entries 1 to 5