#### 15.6.3.5 Temporary Tablespaces

`InnoDB` uses session temporary tablespaces and a global temporary tablespace.

##### Session Temporary Tablespaces

 Session temporary tablespaces store user-created temporary tables and internal temporary tables created by the optimizer when `InnoDB` is configured as the storage engine for on-disk internal temporary tables. Beginning with MySQL 8.0.16, the storage engine used for on-disk internal temporary tables is `InnoDB`. (Previously, the storage engine was determined by the value of [`internal_tmp_disk_storage_engine`](server-system-variables.html#sysvar_internal_tmp_disk_storage_engine).)

 Session temporary tablespaces are allocated to a session from a pool of temporary tablespaces on the first request to create an on-disk temporary table. A maximum of two tablespaces is allocated to a session, one for user-created temporary tables and the other for internal temporary tables created by the optimizer. The temporary tablespaces allocated to a session are used for all on-disk temporary tables created by the session. When a session disconnects, its temporary tablespaces are truncated and released back to the pool. A pool of 10 temporary tablespaces is created when the server is started. The size of the pool never shrinks and tablespaces are added to the pool automatically as necessary. The pool of temporary tablespaces is removed on normal shutdown or on an aborted initialization. Session temporary tablespace files are five pages in size when created and have an `.ibt` file name extension.

 A range of 400 thousand space IDs is reserved for session temporary tablespaces. Because the pool of session temporary tablespaces is recreated each time the server is started, space IDs for session temporary tablespaces are not persisted when the server is shut down, and may be reused.

 The [`innodb_temp_tablespaces_dir`](innodb-parameters.html#sysvar_innodb_temp_tablespaces_dir) variable defines the location where session temporary tablespaces are created. The default location is the `#innodb_temp` directory in the data directory. Startup is refused if the pool of temporary tablespaces cannot be created.

```
$> cd BASEDIR/data/#innodb_temp
$> ls
temp_10.ibt  temp_2.ibt  temp_4.ibt  temp_6.ibt  temp_8.ibt
temp_1.ibt   temp_3.ibt  temp_5.ibt  temp_7.ibt  temp_9.ibt
```

 In statement based replication (SBR) mode, temporary tables created on a replica reside in a single session temporary tablespace that is truncated only when the MySQL server is shut down.

 The [`INNODB_SESSION_TEMP_TABLESPACES`](information-schema-innodb-session-temp-tablespaces-table.html) table provides metadata about session temporary tablespaces.

 The [`INFORMATION_SCHEMA.INNODB_TEMP_TABLE_INFO`](information-schema-innodb-temp-table-info-table.html) table provides metadata about user-created temporary tables that are active in an `InnoDB` instance.

##### Global Temporary Tablespace

 The global temporary tablespace (`ibtmp1`) stores rollback segments for changes made to user-created temporary tables.

 The [`innodb_temp_data_file_path`](innodb-parameters.html#sysvar_innodb_temp_data_file_path) variable defines the relative path, name, size, and attributes for global temporary tablespace data files. If no value is specified for [`innodb_temp_data_file_path`](innodb-parameters.html#sysvar_innodb_temp_data_file_path), the default behavior is to create a single auto-extending data file named `ibtmp1` in the [`innodb_data_home_dir`](innodb-parameters.html#sysvar_innodb_data_home_dir) directory. The initial file size is slightly larger than 12MB.

 The global temporary tablespace is removed on normal shutdown or on an aborted initialization, and recreated each time the server is started. The global temporary tablespace receives a dynamically generated space ID when it is created. Startup is refused if the global temporary tablespace cannot be created. The global temporary tablespace is not removed if the server halts unexpectedly. In this case, a database administrator can remove the global temporary tablespace manually or restart the MySQL server. Restarting the MySQL server removes and recreates the global temporary tablespace automatically.

 The global temporary tablespace cannot reside on a raw device.

[`INFORMATION_SCHEMA.FILES`](information-schema-files-table.html) provides metadata about the global temporary tablespace. Issue a query similar to this one to view global temporary tablespace metadata:

```
mysql> SELECT * FROM INFORMATION_SCHEMA.FILES WHERE TABLESPACE_NAME='innodb_temporary'\G
```

 By default, the global temporary tablespace data file is autoextending and increases in size as necessary.

 To determine if a global temporary tablespace data file is autoextending, check the [`innodb_temp_data_file_path`](innodb-parameters.html#sysvar_innodb_temp_data_file_path) setting:

```
mysql> SELECT @@innodb_temp_data_file_path;
+------------------------------+
| @@innodb_temp_data_file_path |
+------------------------------+
| ibtmp1:12M:autoextend        |
+------------------------------+
```

 To check the size of global temporary tablespace data files, query the [`INFORMATION_SCHEMA.FILES`](information-schema-files-table.html) table using a query similar to this one:

```
mysql> SELECT FILE_NAME, TABLESPACE_NAME, ENGINE, INITIAL_SIZE, TOTAL_EXTENTS*EXTENT_SIZE
       AS TotalSizeBytes, DATA_FREE, MAXIMUM_SIZE FROM INFORMATION_SCHEMA.FILES
       WHERE TABLESPACE_NAME = 'innodb_temporary'\G
*************************** 1. row ***************************
      FILE_NAME: ./ibtmp1
TABLESPACE_NAME: innodb_temporary
         ENGINE: InnoDB
   INITIAL_SIZE: 12582912
 TotalSizeBytes: 12582912
      DATA_FREE: 6291456
   MAXIMUM_SIZE: NULL
```

`TotalSizeBytes` shows the current size of the global temporary tablespace data file. For information about other field values, see [Section 26.3.15, “The INFORMATION\_SCHEMA FILES Table”](information-schema-files-table.html).

 Alternatively, check the global temporary tablespace data file size on your operating system. The global temporary tablespace data file is located in the directory defined by the [`innodb_temp_data_file_path`](innodb-parameters.html#sysvar_innodb_temp_data_file_path) variable.

 To reclaim disk space occupied by a global temporary tablespace data file, restart the MySQL server. Restarting the server removes and recreates the global temporary tablespace data file according to the attributes defined by [`innodb_temp_data_file_path`](innodb-parameters.html#sysvar_innodb_temp_data_file_path).

 To limit the size of the global temporary tablespace data file, configure [`innodb_temp_data_file_path`](innodb-parameters.html#sysvar_innodb_temp_data_file_path) to specify a maximum file size. For example:

```
[mysqld]
innodb_temp_data_file_path=ibtmp1:12M:autoextend:max:500M
```

 Configuring [`innodb_temp_data_file_path`](innodb-parameters.html#sysvar_innodb_temp_data_file_path) requires restarting the server.

