The System Tablespace

 The system tablespace is the storage area for the InnoDB data dictionary, the doublewrite buffer, the change buffer, and undo logs. It may also contain table and index data if tables are created in the system tablespace rather than file-per-table or general tablespaces.

The system tablespace can have one or more data files. By default, a single system tablespace data file, named ibdata1, is created in the data directory. The size and number of system tablespace data files is defined by the innodb_data_file_path startup option. For configuration information, see System Tablespace Data File Configuration.

Additional information about the system tablespace is provided under the following topics in the section:

• Resizing the System Tablespace

• Using Raw Disk Partitions for the System Tablespace

Resizing the System Tablespace

This section describes how to increase or decrease the size of the system tablespace.

Increasing the Size of the System Tablespace

The easiest way to increase the size of the system tablespace is to configure it to be auto-extending. To do so, specify the autoextend attribute for the last data file in the innodb_data_file_path setting, and restart the server. For example:

The ENUM Type

 An ENUM is a string object with a value chosen from a list of permitted values that are enumerated explicitly in the column specification at table creation time.

See Section 11.3.1, “String Data Type Syntax” for ENUM type syntax and length limits.

The ENUM type has these advantages:

• Compact data storage in situations where a column has a limited set of possible values. The strings you specify as input values are automatically encoded as numbers. See Section 11.7, “Data Type Storage Requirements” for storage requirements for the ENUM type.

• Readable queries and output. The numbers are translated back to the corresponding strings in query results.

and these potential issues to consider:

• If you make enumeration values that look like numbers, it is easy to mix up the literal values with their internal index numbers, as explained in Enumeration Limitations.

• Using ENUM columns in ORDER BY clauses requires extra care, as explained in Enumeration Sorting.

• Creating and Using ENUM Columns

• Index Values for Enumeration Literals

• Handling of Enumeration Literals

• Empty or NULL Enumeration Values

• Enumeration Sorting

• Enumeration Limitations