14.6.1.3 Importing InnoDB Tables

This section describes how to import tables using the Transportable Tablespaces feature, which permits importing tables that reside in file-per-table tablespaces. There are many reasons why you might want to import tables:

To run reports on a non-production MySQL server instance to avoid placing extra load on a production server.
To copy data to a new replica server.
To restore a table from a backed-up tablespace file.
As a faster way of moving data than importing a dump file, which requires reinserting data and rebuilding indexes.
To move a data to a server with storage media that is better suited to your storage requirements. For example, you might move busy tables to an SSD device, or move large tables to a high-capacity HDD device.

The Transportable Tablespaces feature is described under the following topics in this section:

Prerequisites

The innodb_file_per_table variable must be enabled, which it is by default.
The page size of the tablespace must match the page size of the destination MySQL server instance. InnoDB page size is defined by the innodb_page_size variable, which is configured when initializing a MySQL server instance.
If the table is in a foreign key relationship, foreign_key_checks must be disabled before executing DISCARD TABLESPACE. Also, you should export all foreign key related tables at the same logical point in time, as the ALTER TABLE ... IMPORT TABLESPACE feature does not enforce foreign key constraints on imported data. To do so, stop updating the related tables, commit all transactions, acquire shared locks on the tables, and perform the export operations.
When importing a table from another MySQL server instance, both MySQL server instances must have General Availability (GA) status and must be the same version. Otherwise, the table must be created on the same MySQL server instance into which it is being imported.
If the table was created outside of the data directory by specifying the DATA DIRECTORY clause in the CREATE TABLE statement, the table that you replace on the destination instance must be defined with the same DATA DIRECTORY clause. A schema mismatch error is reported if the clauses do not match. To determine if the source table was defined with a DATA DIRECTORY clause, use SHOW CREATE TABLE to view the table definition. For information about using the DATA DIRECTORY clause, see Section 14.6.1.2, “Creating Tables Externally”.

Importing a Tablespace

This example demonstrates how to import a table that resides in a file-per-table tablespace.

On the destination instance, create a table with the same definition as the table you intend to import. (You can obtain the table definition using SHOW CREATE TABLE syntax.) If the table definition does not match, a schema mismatch error is reported when you attempt the import operation.
```
mysql> USE test;
mysql> CREATE TABLE t1 (c1 INT) ENGINE=INNODB;
```
On the destination instance, discard the tablespace of the table that you just created. (Before importing, you must discard the tablespace of the receiving table.)
```
mysql> ALTER TABLE t1 DISCARD TABLESPACE;
```
On the source instance, run FLUSH TABLES ... FOR EXPORT to quiesce the table you intend to import. When a table is quiesced, only read-only transactions are permitted on the table.
```
mysql> USE test;
mysql> FLUSH TABLES t1 FOR EXPORT;
```
FLUSH TABLES ... FOR EXPORT ensures that changes to the named table are flushed to disk so that a binary table copy can be made while the server is running. When FLUSH TABLES ... FOR EXPORT is run, InnoDB generates a .cfg metadata file in the schema directory of the table. The .cfg file contains metadata that is used for schema verification during the import operation.
Copy the .ibd file and .cfg metadata file from the source instance to the destination instance. For example:
```
shell> scp /path/to/datadir/test/t1.{ibd,cfg} destination-server:/path/to/datadir/test
```
The .ibd file and .cfg file must be copied before releasing the shared locks, as described in the next step.
On the source instance, use UNLOCK TABLES to release the locks acquired by the FLUSH TABLES ... FOR EXPORT statement:
```
mysql> USE test;
mysql> UNLOCK TABLES;
```

On the destination instance, import the tablespace:

mysql> USE test;
mysql> ALTER TABLE t1 IMPORT TABLESPACE;

Limitations

The Transportable Tablespaces feature is only supported for tables that reside in file-per-table tablespaces. It is not supported for the tables that reside in the system tablespace. Tables in the system tablespace cannot be quiesced.
DISCARD TABLESPACE is not supported for partitioned tables, which means that importing partitioned tables is not supported. If you run ALTER TABLE ... DISCARD TABLESPACE on a partitioned table, the following error is returned: ERROR 1031 (HY000): Table storage engine for 'part' doesn't have this option.
FLUSH TABLES ... FOR EXPORT is not supported on tables with a FULLTEXT index, as full-text search auxiliary tables cannot be flushed. After importing a table with a FULLTEXT index, run OPTIMIZE TABLE to rebuild the FULLTEXT indexes. Alternatively, drop FULLTEXT indexes before the export operation and recreate the indexes after importing the table on the destination instance.

Usage Notes

A .cfg metadata file is not required to import a table. However, metadata checks are not performed when importing without a .cfg file, and a warning similar to the following is issued:
```
Message: InnoDB: IO Read error: (2, No such file or directory) Error opening '.\
test\t.cfg', will attempt to import without schema verification
1 row in set (0.00 sec)
```
Importing without a .cfg metadata file should only be considered if no schema mismatches are expected. The ability to import without a .cfg file could be useful in crash recovery scenarios where metadata is not accessible.
On Windows, InnoDB stores database, tablespace, and table names internally in lowercase. To avoid import problems on case-sensitive operating systems such as Linux and Unix, create all databases, tablespaces, and tables using lowercase names. A convenient way to accomplish this is to add lower_case_table_names=1 to the [mysqld] section of your my.cnf or my.ini file before creating databases, tablespaces, or tables:
```
[mysqld]
lower_case_table_names=1
```

Internals

The following information describes internals and messages written to the error log during a table import procedure.

When ALTER TABLE ... DISCARD TABLESPACE is run on the destination instance:

The table is locked in X mode.
The tablespace is detached from the table.

When FLUSH TABLES ... FOR EXPORT is run on the source instance:

The table being flushed for export is locked in shared mode.
The purge coordinator thread is stopped.
Dirty pages are synchronized to disk.
Table metadata is written to the binary .cfg file.

Expected error log messages for this operation:

[Note] InnoDB: Sync to disk of '"test"."t1"' started.
[Note] InnoDB: Stopping purge
[Note] InnoDB: Writing table metadata to './test/t1.cfg'
[Note] InnoDB: Table '"test"."t1"' flushed to disk

When UNLOCK TABLES is run on the source instance:

The binary .cfg file is deleted.
The shared lock on the table being imported is released and the purge coordinator thread is restarted.

Expected error log messages for this operation:

[Note] InnoDB: Deleting the meta-data file './test/t1.cfg'
[Note] InnoDB: Resuming purge

When ALTER TABLE ... IMPORT TABLESPACE is run on the destination instance, the import algorithm performs the following operations for the tablespace being imported:

Each tablespace page is checked for corruption.
The space ID and log sequence numbers (LSNs) on each page are updated.
Flags are validated and LSN updated for the header page.
Btree pages are updated.
The page state is set to dirty so that it is written to disk.

Expected error log messages for this operation:

[Note] InnoDB: Importing tablespace for table 'test/t1' that was exported
from host 'host_name'
[Note] InnoDB: Phase I - Update all pages
[Note] InnoDB: Sync to disk
[Note] InnoDB: Sync to disk - done!
[Note] InnoDB: Phase III - Flush changes to disk
[Note] InnoDB: Phase IV - Flush complete

Note

You may also receive a warning that a tablespace is discarded (if you discarded the tablespace for the destination table) and a message stating that statistics could not be calculated due to a missing .ibd file:

[Warning] InnoDB: Table "test"."t1" tablespace is set as discarded.
7f34d9a37700 InnoDB: cannot calculate statistics for table
"test"."t1" because the .ibd file is missing. For help, please refer to
http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html