14.16.7 InnoDB INFORMATION_SCHEMA Temporary Table Info Table

INNODB_TEMP_TABLE_INFO provides information about user-created InnoDB temporary tables that are active in the InnoDB instance. It does not provide information about internal InnoDB temporary tables used by the optimizer.

mysql> SHOW TABLES FROM INFORMATION_SCHEMA LIKE 'INNODB_TEMP%';
+---------------------------------------------+
| Tables_in_INFORMATION_SCHEMA (INNODB_TEMP%) |
+---------------------------------------------+
| INNODB_TEMP_TABLE_INFO                      |
+---------------------------------------------+

For the table definition, see Section 24.4.27, “The INFORMATION_SCHEMA INNODB_TEMP_TABLE_INFO Table”.

Example 14.12 INNODB_TEMP_TABLE_INFO

This example demonstrates characteristics of the INNODB_TEMP_TABLE_INFO table.

Create a simple InnoDB temporary table:

mysql> CREATE TEMPORARY TABLE t1 (c1 INT PRIMARY KEY) ENGINE=INNODB;

Query INNODB_TEMP_TABLE_INFO to view the temporary table metadata.
```
mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_TEMP_TABLE_INFO\G
*************************** 1. row ***************************
            TABLE_ID: 194
                NAME: #sql7a79_1_0
              N_COLS: 4
               SPACE: 182
PER_TABLE_TABLESPACE: FALSE
       IS_COMPRESSED: FALSE
```
The TABLE_ID is a unique identifier for the temporary table. The NAME column displays the system-generated name for the temporary table, which is prefixed with “#sql”. The number of columns (N_COLS) is 4 rather than 1 because InnoDB always creates three hidden table columns (DB_ROW_ID, DB_TRX_ID, and DB_ROLL_PTR). PER_TABLE_TABLESPACE and IS_COMPRESSED report TRUE for compressed temporary tables. Otherwise, these fields report FALSE.

Create a compressed temporary table.

mysql> CREATE TEMPORARY TABLE t2 (c1 INT) ROW_FORMAT=COMPRESSED ENGINE=INNODB;

Query INNODB_TEMP_TABLE_INFO again.

mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_TEMP_TABLE_INFO\G
*************************** 1. row ***************************
            TABLE_ID: 195
                NAME: #sql7a79_1_1
              N_COLS: 4
               SPACE: 183
PER_TABLE_TABLESPACE: TRUE
       IS_COMPRESSED: TRUE
*************************** 2. row ***************************
            TABLE_ID: 194
                NAME: #sql7a79_1_0
              N_COLS: 4
               SPACE: 182
PER_TABLE_TABLESPACE: FALSE
       IS_COMPRESSED: FALSE

PER_TABLE_TABLESPACE and IS_COMPRESSED report TRUE for the compressed temporary table. The SPACE ID for the compressed temporary table is different because compressed temporary tables are created in separate file-per-table tablespaces. Non-compressed temporary tables are created in the shared temporary tablespace (ibtmp1) and report the same SPACE ID.

Restart MySQL and query INNODB_TEMP_TABLE_INFO.
```
mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_TEMP_TABLE_INFO\G
Empty set (0.00 sec)
```
An empty set is returned because INNODB_TEMP_TABLE_INFO and its data are not persisted to disk when the server is shut down.

Create a new temporary table.

mysql> CREATE TEMPORARY TABLE t1 (c1 INT PRIMARY KEY) ENGINE=INNODB;

Query INNODB_TEMP_TABLE_INFO to view the temporary table metadata.

mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_TEMP_TABLE_INFO\G
*************************** 1. row ***************************
            TABLE_ID: 196
                NAME: #sql7b0e_1_0
              N_COLS: 4
               SPACE: 184
PER_TABLE_TABLESPACE: FALSE
       IS_COMPRESSED: FALSE

The SPACE ID may be different because it is dynamically generated when the server is started.