MariaDB Enterprise Server InnoDB AUTO_INCREMENT Columns

For best performance, every InnoDB table should have a primary key column. If your table does not have a column or a set of columns that could act as a natural primary key, then you can define a single AUTO_INCREMENT column, which can serve as the table's primary key.

Note

If you are using versions later than MariaDB Enterprise Server 10.3 or MariaDB Community Server 10.3, then sequences can be used instead of AUTO_INCREMENT columns. Sequences are compliant with the SQL standard, while AUTO_INCREMENT columns are not, so sequences are the better option for applications that require standard-compliant features. See InnoDB Sequences for more information.

Choosing a Data Type for an AUTO_INCREMENT Column

When designing a schema, AUTO_INCREMENT columns should use integer data types. The following types can be used:

Data Type

Signed Range

Unsigned Range

TINYINT

-128 - 127

0 - 255

SMALLINT

-32768 - 32767

0 - 65535

MEDIUMINT

-8388608 - 8388607

0 - 16777215

INT

-2147483648 - 2147483647

0 - 4294967295

BIGINT

-9223372036854775808 - 9223372036854775807

0 - 18446744073709551615

To determine which type to use, consider the following points:

  1. Do you want to be able to manually insert negative values? If not, then specify the UNSIGNED attribute for the column.

    InnoDB can't generate negative AUTO_INCREMENT values, so it is only beneficial to use a signed integer column if you want the option to manually insert negative values, which would bypass the AUTO_INCREMENT handling.

  2. How large will your table grow?

    If your AUTO_INCREMENT column is being used as the table's primary key, then the maximum value for the chosen data type should be considered the maximum number of rows that can fit in the table:

    Data Type

    Maximum Number of Rows (Signed)

    Maximum Number of Rows (Unsigned)

    TINYINT

    127

    255

    SMALLINT

    32767

    65535

    MEDIUMINT

    8388607

    16777215

    INT

    2147483647

    4294967295

    BIGINT

    9223372036854775807

    18446744073709551615

    If you want to give your table the most room to grow, then it would be best to choose BIGINT UNSIGNED.

Creating an InnoDB Table with an AUTO_INCREMENT Column

Let's create an InnoDB table with an AUTO_INCREMENT column after confirming that the default storage engine is InnoDB:

  1. Connect to the server using MariaDB Client:

    $ mariadb --user=root
    
  2. Confirm that the default storage engine is InnoDB by checking the default_storage_engine system variable using the SHOW SESSION VARIABLES statement:

    SHOW SESSION VARIABLES
       LIKE 'default_storage_engine';
    
    +------------------------+--------+
    | Variable_name          | Value  |
    +------------------------+--------+
    | default_storage_engine | InnoDB |
    +------------------------+--------+
    
  3. If the database does not exist, then create the database for the table using the CREATE DATABASE statement:

    CREATE DATABASE hq_sales;
    
  4. Create the table using the CREATE TABLE statement:

    CREATE TABLE hq_sales.invoices (
       invoice_id BIGINT UNSIGNED AUTO_INCREMENT NOT NULL,
       branch_id INT NOT NULL,
       customer_id INT,
       invoice_date DATETIME(6),
       invoice_total DECIMAL(13, 2),
       payment_method ENUM('NONE', 'CASH', 'WIRE_TRANSFER', 'CREDIT_CARD', 'GIFT_CARD'),
       PRIMARY KEY(invoice_id)
    );
    

Inserting a Row with an AUTO_INCREMENT Column

If a column is specified as AUTO_INCREMENT, then its value will be automatically generated. There are multiple ways to insert rows with these automatically generated values.

Omitting the Column

If the column is not specified, then InnoDB will automatically generate the value.

Let's insert a row into the table created in the Creating an InnoDB Table with an AUTO_INCREMENT Column section:

  1. Connect to the server using MariaDB Client:

    $ mariadb --user=root
    
  2. Insert a row with the INSERT statement, but do not specify the AUTO_INCREMENT column:

    INSERT INTO hq_sales.invoices
       (branch_id, customer_id, invoice_date, invoice_total, payment_method)
    VALUES
       (1, 1, '2020-05-10 12:35:10', 1087.23, 'CREDIT_CARD');
    
  3. Select the same row with the SELECT statement to confirm that a value was automatically generated:

    SELECT invoice_id
    FROM hq_sales.invoices
    WHERE branch_id = 1
    AND customer_id = 1
    AND invoice_date = '2020-05-10 12:35:10';
    
    +------------+
    | invoice_id |
    +------------+
    |          1 |
    +------------+
    

Specifying the Column's Value as 0

If the column's value is specified as 0, then InnoDB will automatically generate the value if the sql_mode system variable does not contain NO_AUTO_VALUE_ON_ZERO.

Let's insert a row into the table created in the Creating an InnoDB Table with an AUTO_INCREMENT Column section:

  1. Connect to the server using MariaDB Client:

    $ mariadb --user=root
    
  2. Confirm that the session's value of the sql_mode system variable does not contain NO_AUTO_VALUE_ON_ZERO with the SHOW SESSION VARIABLES statement:

    SHOW SESSION VARIABLES
       LIKE 'sql_mode';
    
    +---------------+-------------------------------------------------------------------------------------------+
    | Variable_name | Value                                                                                     |
    +---------------+-------------------------------------------------------------------------------------------+
    | sql_mode      | STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
    +---------------+-------------------------------------------------------------------------------------------+
    
  3. Insert a row with the INSERT statement, and specify the AUTO_INCREMENT column's value as 0:

    INSERT INTO hq_sales.invoices
       (invoice_id, branch_id, customer_id, invoice_date, invoice_total, payment_method)
    VALUES
       (0, 1, 2, '2020-05-10 14:17:32', 1508.57, 'WIRE_TRANSFER');
    
  4. Select the same row with the SELECT statement to confirm that a value was automatically generated:

    SELECT invoice_id
    FROM hq_sales.invoices
    WHERE branch_id = 1
    AND customer_id = 2
    AND invoice_date = '2020-05-10 14:17:32';
    
    +------------+
    | invoice_id |
    +------------+
    |          2 |
    +------------+
    

Specifying the Column's Value as NULL

If the column's value is specified as NULL, then InnoDB will automatically generate the value if the column is defined as NOT NULL.

Let's insert a row into the table created in the Creating an InnoDB Table with an AUTO_INCREMENT Column section:

  1. Connect to the server using MariaDB Client:

    $ mariadb --user=root
    
  2. Insert a row with the INSERT statement, and specify the AUTO_INCREMENT column's value as NULL:

    INSERT INTO hq_sales.invoices
       (invoice_id, branch_id, customer_id, invoice_date, invoice_total, payment_method)
    VALUES
       (NULL, 1, 3, '2020-05-10 14:25:16', 227.15, 'CASH');
    
  3. Select the same row with the SELECT statement to confirm that a value was automatically generated:

    SELECT invoice_id
    FROM hq_sales.invoices
    WHERE branch_id = 1
    AND customer_id = 3
    AND invoice_date = '2020-05-10 14:25:16';
    
    +------------+
    | invoice_id |
    +------------+
    |          3 |
    +------------+
    

Getting the Last Inserted AUTO_INCREMENT Value

After InnoDB inserts an automatically generated value into an AUTO_INCREMENT column, the application sometimes needs to know what value it inserted. For example, the application may need to use the value to insert a foreign key column in a dependent table. The LAST_INSERT_ID() function can be used to get the lasted inserted value for an AUTO_INCREMENT column without re-reading the row from the table.

Let's insert a row into the table created in the Creating an InnoDB Table with an AUTO_INCREMENT Column section and then use the LAST_INSERT_ID() function:

  1. Connect to the server using MariaDB Client:

    $ mariadb --user=root
    
  2. Insert a row with the INSERT statement, but do not specify the AUTO_INCREMENT column:

    INSERT INTO hq_sales.invoices
       (branch_id, customer_id, invoice_date, invoice_total, payment_method)
    VALUES
       (1, 4, '2020-05-10 12:37:22', 104.19, 'CREDIT_CARD');
    
  3. Execute the LAST_INSERT_ID() function to get the AUTO_INCREMENT value for the new row:

    SELECT LAST_INSERT_ID();
    
    +------------------+
    | LAST_INSERT_ID() |
    +------------------+
    |                4 |
    +------------------+
    
  4. Select the same row with the SELECT statement to confirm that the AUTO_INCREMENT column has the same value:

    SELECT invoice_id
    FROM hq_sales.invoices
    WHERE branch_id = 1
    AND customer_id = 4
    AND invoice_date = '2020-05-10 12:37:22';
    
    +------------+
    | invoice_id |
    +------------+
    |          4 |
    +------------+
    

Choosing an AUTO_INCREMENT Lock Mode for InnoDB

When multiple rows are inserted into a table concurrently, InnoDB needs to be able to generate multiple values concurrently in a safe manner. It has several different modes that can be used to do this, and each mode has its own advantages and disadvantages.

InnoDB's AUTO_INCREMENT lock mode is configured with the innodb_autoinc_lock_mode system variable. Users can choose between 3 different values:

Value

Description

0

  • This value configures Traditional Lock Mode.

  • Don't use traditional lock mode.

  • Traditional lock mode performs very poorly.

  • In traditional lock mode, InnoDB holds a table-level lock while generating AUTO_INCREMENT values.

1

  • This value configures Consecutive Lock Mode.

  • Consecutive lock mode is the default lock mode.

  • In consecutive lock mode, InnoDB holds a table-level lock while generating AUTO_INCREMENT values for statements that insert multiple new rows. However, InnoDB uses a lightweight internal lock to improve performance when generating an AUTO_INCREMENT value for statements that insert a single new row.

2

  • This value configures Interleaved Lock Mode.

  • Interleaved lock mode is the recommended lock mode for best performance.

  • If Galera Cluster is being used, then interleaved lock mode must be configured.

  • In interleaved lock mode, InnoDB never holds a table-level lock while generating AUTO_INCREMENT values.

  • Interleaved lock mode is not safe to use if binlog_format is set to STATEMENT.

Configuring the AUTO_INCREMENT Lock Mode for InnoDB

The AUTO_INCREMENT Lock Mode for InnoDB is configured by the innodb_autoinc_lock_mode system variable.

  1. Choose a configuration file for custom changes to system variables and options.

    It is not recommended to make custom changes to Enterprise Server's default configuration files, because your custom changes can be overwritten by other default configuration files that are loaded after.

    Ensure that your custom changes will be read last by creating a custom configuration file in one of the included directories. Configuration files in included directories are read in alphabetical order. Ensure that your custom configuration file is read last by using the z- prefix in the file name.

    Some example configuration file paths for different distributions are shown in the following table:

    Distributions

    Example configuration file path

    CentOS
    RHEL
    SLES

    /etc/my.cnf.d/z-custom-mariadb.cnf

    Debian
    Ubuntu

    /etc/mysql/mariadb.conf.d/z-custom-mariadb.cnf

  1. Set the innodb_autoinc_lock_mode system variable in the configuration file.

    It needs to be set in a group that will be read by MariaDB Server, such as [mariadb] or [server].

    For example:

    [mariadb]
    ...
    innodb_autoinc_lock_mode = 2
    
  2. Restart the server:

    $ sudo systemctl restart mariadb
    

Setting a Table's Next AUTO_INCREMENT Value

A table's next AUTO_INCREMENT value can be set with the ALTER TABLE statement. The value is set using the AUTO_INCREMENT table option.

Let's alter the AUTO_INCREMENT value for the table created in the Creating an InnoDB Table with an AUTO_INCREMENT Column section and then insert a row into the table, so we can confirm that it uses the new value:

  1. Connect to the server using MariaDB Client:

    $ mariadb --user=root
    
  2. Alter the table's next AUTO_INCREMENT value with the ALTER TABLE statement:

    ALTER TABLE hq_sales.invoices
       AUTO_INCREMENT = 100;
    
  3. Insert a row with the INSERT statement, but do not specify the AUTO_INCREMENT column:

    INSERT INTO hq_sales.invoices
       (branch_id, customer_id, invoice_date, invoice_total, payment_method)
    VALUES
       (1, 5, '2020-05-10 12:43:19', 1105.98, 'CREDIT_CARD');
    
  4. Execute the LAST_INSERT_ID() function to get the AUTO_INCREMENT value for the new row:

    SELECT LAST_INSERT_ID();
    
    +------------------+
    | LAST_INSERT_ID() |
    +------------------+
    |              100 |
    +------------------+
    
  5. Select the same row with the SELECT statement to confirm that the AUTO_INCREMENT column has the same value:

    SELECT invoice_id
    FROM hq_sales.invoices
    WHERE branch_id = 1
    AND customer_id = 5
    AND invoice_date = '2020-05-10 12:43:19';
    
    +------------+
    | invoice_id |
    +------------+
    |        100 |
    +------------+
    

Configure the Offset and Increment Values

The offset and increment values can be configured by setting the auto_increment_offset and auto_increment_increment system variables.

When Galera Cluster is used, the offset and increment values are managed automatically by default. They can be managed manually by disabling the wsrep_auto_increment_control system variable.