You can store each
InnoDB table and its
indexes in its own data file. This feature is called
“file-per-table tablespaces” because in effect each
table has its own tablespace.
You can reclaim disk space when truncating or dropping a
table stored in a file-per-table tablepace. Truncating or
dropping tables stored in the system tablespace creates free
space internally in the system tablespace data files
(ibdata files) which
can only be used for new
TRUNCATE TABLE operation
is faster when run on individual
You can store specific tables on separate storage devices, for I/O optimization, space management, or backup purposes.
You can run
OPTIMIZE TABLE to
compact or recreate a file-per-table tablespace. When you
InnoDB creates a new
.ibd file with a temporary name, using
only the space required to store actual data. When the
optimization is complete,
.ibd file and replaces it with
the new one. If the previous
grew significantly but the actual data only accounted for a
portion of its size, running
TABLE can reclaim the unused space.
You can move individual
rather than entire databases.
You can enable more efficient storage for tables with large
using the dynamic
File-per-table tablespaces may improve chances for a successful recovery and save time when a corruption occurs, when a server cannot be restarted, or when backup and binary logs are unavailable.
You can back up or restore a single table quickly, without
interrupting the use of other
You can excluded tables stored in file-per-table tablespaces from a backup. This is beneficial if you have tables that require backup less frequently or on a different schedule.
File-per-table tablespaces are convenient for per-table status reporting when copying or backing up tables.
You can monitor table size at a file system level, without accessing MySQL.
Common Linux file systems do not permit concurrent writes to
a single file when
innodb_flush_method is set
O_DIRECT. As a result, there are
possible performance improvements when using
The system tablespace stores the data dictionary and undo logs, and has a 64TB size limit. By comparison, each file-per-table tablespace has a 64TB size limit, which provides you with room for growth. See Section D.7.3, “Limits on Table Size” for related information.
With file-per-table tablespaces, each table may have unused space, which can only be utilized by rows of the same table. This could lead to wasted space if not properly managed.
fsync operations must run on each open
table rather than on a one file. Because there is a separate
fsync operation for each file, write
operations on multiple tables cannot be combined into a
single I/O operation. This may require
InnoDB to perform a higher total number
mysqld must keep one open file handle per table, which may impact performance if you have numerous tables in file-per-table tablespaces.
More file descriptors are used.
If many tables are growing there is potential for more
fragmentation which can impede
TABLE and table scan performance. However, when
fragmentation is managed, having files in their own
tablespace can improve performance.
The buffer pool is scanned when dropping a file-per-table tablespace, which can take several seconds for buffer pools that are tens of gigabytes in size. The scan is performed with a broad internal lock, which may delay other operations. Tables in the system tablespace are not affected.
variable, which defines increment size (in MB) for extending
the size of an auto-extending shared tablespace file when it
becomes full, does not apply to file-per-table tablespace
files, which are auto-extending regardless of the
setting. The initial extensions are by small amounts, after
which extensions occur in increments of 4MB.
To enable file-per-table tablespaces, start the server with the
For example, add a line to the
InnoDB stores each newly created
table in its own
file in the database directory where the table belongs. This is
similar to what the
MyISAM storage engine
MyISAM divides the table into a
data file and an
index file. For
InnoDB, the data and the
indexes are stored together in the
file is still created as usual.
You cannot freely move
.ibd files between
database directories as you can with
table files. This is because the table definition that is stored
InnoDB shared tablespace includes the
database name, and because
preserve the consistency of transaction IDs and log sequence
If you remove the
innodb_file_per_table line from
my.cnf and restart the server, newly
InnoDB tables are created inside the
shared tablespace files again.
option affects only table creation, not access to existing
tables. If you start the server with this option, new tables are
.ibd files, but you can still
access tables that exist in the shared tablespace. If you start
the server without this option, new tables are created in the
shared tablespace, but you can still access tables created in
InnoDB requires the shared tablespace to
store its internal data dictionary and undo logs. The
.ibd files alone are not sufficient for
InnoDB to operate.
To move an
.ibd file and the associated
table from one database to another, use a
RENAME TABLE statement:
If you have a “clean” backup of an
.ibd file, you can restore it to the MySQL
installation from which it originated as follows:
In this context, a “clean”
.ibd file backup is one for which the
following requirements are satisfied:
There are no uncommitted modifications by transactions in
There are no unmerged insert buffer entries in the
Purge has removed all delete-marked index records from the
mysqld has flushed all modified pages of
.ibd file from the buffer pool to
You can make a clean backup
.ibd file using
the following method:
Another method for making a clean copy of an
.ibd file is to use the commercial
InnoDB Hot Backup tool:
Use InnoDB Hot Backup to back up the
Start a second mysqld server on the
backup and let it clean up the
files in the backup.