I would like to understand these ibdata files as these play vital role in the crash recovery procedure. I could not find proper resources over the web for this.
1 Answer
ibdata1
The file ibdata1
is the system tablespace for the InnoDB infrastructure.
It contains several classes for information vital for InnoDB
- Table Data Pages
- Table Index Pages
- Data Dictionary
- MVCC Control Data
- Undo Space
- Rollback Segments
- Double Write Buffer (Pages Written in the Background to avoid OS caching)
- Insert Buffer (Changes to Secondary Indexes)
Click Here to see a Pictorial Representation
You can divorce Data and Index Pages from ibdata1 by enabling innodb_file_per_table. This will cause any newly created InnoDB table to store data and index pages in an external .ibd
file.
Example
- datadir is
/var/lib/mysql
CREATE TABLE mydb.mytable (...) ENGINE=InnoDB;
, creates/var/lib/mysql/mydb/mytable.frm
innodb_file_per_table
enabled, Data/Index Pages Stored in/var/lib/mysql/mydb/mytable.ibd
innodb_file_per_table
disabled, Data/Index Pages Stored inibdata1
No matter where the InnoDB table is stored, InnoDB's functionality requires looking for table metadata and storing and retrieving MVCC info to support ACID compliance and Transaction Isolation.
Here are my past articles on separating table data and indexes from ibdata1
Oct 29, 2010
: My Original Post in StackOverflowNov 26, 2011
: ERROR 1114 (HY000) at line 6308 in file & The table user_analysis is fullFeb 03, 2012
: Scheduled optimization of tables in MySQL InnoDBMar 25, 2012
: Why does InnoDB store all databases in one file?Apr 01, 2012
: Is innodb_file_per_table advisable?
iblog files (a.k.a. ib_logfile0
, ib_logfile1
)
If you want to know what the ib_logfile0
and ib_logfile1
are for, they are the InnoDB Redo Logs. They should never be erased or resized until a full normal shutdown of mysqld has taken place. If mysqld ever crashes, just start up mysqld. It will read across ib_logfile0
and ib_logfile1
to check for any data changes that were not posted to the the double write buffer in ibdata1
. It will replay (redo) those changes. Once they are replayed and stored, mysqld becomes ready for new DB Connections.
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How the space will be retained in these log files... ? I mean to ask... "for new innodb transactions how the same log files be used if these are filled up completely...."– UdayCommented Oct 18, 2012 at 8:44
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1@ Uday The space will not be retained on the iblog files until the logbuffer becomes empty. It is a dynamic process, where the log space get occupied and released based on the stalled transaction changes recorded in the log buffer. These log files get occupied completly, when ever you perform some huge data loads, which leads to Innodb errors stating "InnoDB: which exceeds the log group capacity"., which mean Log file size should be bigger to do things. Hope my explanation cleared your doubt. Commented Nov 11, 2012 at 23:00
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innodb_file_per_table disabled, Data/Index Pages Stored in /var/lib/mysql/mydb/mytable.ibd
andinnodb_file_per_table enbled, Data/Index Pages Stored in ibdata1
should be vice versa, shouldn't it?– rabuddeCommented Sep 21, 2016 at 18:26 -
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