Glossary

LSN
Each InnoDB page (usually 16kb in size) contains a log sequence number, or LSN. The LSN is the system version number for the entire database. Each page’s LSN shows how recently it was changed.
innodb_file_per_table

By default, all InnoDB tables and indexes are stored in the system tablespace on one file. This option causes the server to create one tablespace file per table. To enable it, set it on your configuration file,

[mysqld]
innodb_file_per_table

or start the server with --innodb_file_per_table.

innodb_expand_import

This feature of Percona Server implements the ability to import arbitrary .ibd files exported using the Percona XtraBackup --export option.

See the the full documentation for more information.

innodb_data_home_dir

The directory (relative to :term:` datadir`) where the database server stores the files in a shared tablespace setup. This option does not affect the location of innodb_file_per_table. For example,

[mysqld]
innodb_data_home_dir = ./
innodb_data_file_path

Specifies the names, sizes and location of shared tablespace files:

[mysqld]
innodb_data_file_path=ibdata1:50M;ibdata2:50M:autoextend
innodb_log_group_home_dir

Specifies the location of the InnoDB log files:

[mysqld]
innodb_log_group_home=/var/lib/mysql
innodb_buffer_pool_size

The size in bytes of the memory buffer to cache data and indexes of InnoDB‘s tables. This aims to reduce disk access to provide better performance. By default:

[mysqld]
innodb_buffer_pool_size=8MB
InnoDB
Storage engine which provides ACID-compliant transactions and foreign key support, among others improvements over MyISAM. It is the default engine for MySQL as of the 5.5 series.
MyISAM
Previous default storage engine for MySQL for versions prior to 5.5. It doesn’t fully support transactions but in some scenarios may be faster than InnoDB. Each table is stored on disk in 3 files: .frm, .MYD, .MYI
XtraDB
Percona XtraDB is an enhanced version of the InnoDB storage engine, designed to better scale on modern hardware, and including a variety of other features useful in high performance environments. It is fully backwards compatible, and so can be used as a drop-in replacement for standard InnoDB. More information here .
my.cnf
This file refers to the database server’s main configuration file. Most linux distributions place it as /etc/mysql/my.cnf, but the location and name depends on the particular installation. Note that this is not the only way of configuring the server, some systems does not have one even and rely on the command options to start the server and its defaults values.
datadir
The directory in which the database server stores its databases. Most Linux distribution use /var/lib/mysql by default.
xbstream
To support simultaneous compression and streaming, a new custom streaming format called xbstream was introduced to Percona XtraBackup in addition to the TAR format.
ibdata
Default prefix for tablespace files, e.g. ibdata1 is a 10MB autoextensible file that MySQL creates for the shared tablespace by default.
.frm
For each table, the server will create a file with the .frm extension containing the table definition (for all storage engines).
.ibd
On a multiple tablespace setup (innodb_file_per_table enabled), MySQL will store each newly created table on a file with a .ibd extension.
.MYD
Each MyISAM table has .MYD (MYData) file which contains the data on it.
.MYI
Each MyISAM table has .MYI (MYIndex) file which contains the table’s indexes.
.exp
Files with the .exp extension are created by Percona XtraBackup per each InnoDB tablespace when the xtrabckup --export option is used on prepare. These files can be used to import those tablespaces on Percona Server 5.5 or lower versions, see restoring individual tables
.MRG
Each table using the MERGE storage engine, besides of a .frm file, will have .MRG file containing the names of the MyISAM tables associated with it.
.TRG
File containing the Triggers associated to a table, e.g. :file:`mytable.TRG. With the .TRN file, they represent all the Trigger definitions.
.TRN
File containing the Triggers’ Names associated to a table, e.g. :file:`mytable.TRN. With the .TRG file, they represent all the Trigger definitions.
.ARM
Each table with the Archive Storage Engine has .ARM file which contains the metadata of it.
.ARZ
Each table with the Archive Storage Engine has .ARZ file which contains the data of it.
.CSM
Each table with the CSV Storage Engine has .CSM file which contains the metadata of it.
.CSV
Each table with the CSV Storage engine has .CSV file which contains the data of it (which is a standard Comma Separated Value file).
.opt
MySQL stores options of a database (like charset) in a file with a .opt extension in the database directory.
.par
Each partitioned table has .par file which contains metadata about the partitions.
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