14.19.3 Troubleshooting InnoDB Data Dictionary Operations

Information about table definitions is stored both in the .frm files, and in the InnoDB data dictionary. If you move .frm files around, or if the server crashes in the middle of a data dictionary operation, these sources of information can become inconsistent.

If a data dictionary corruption or consistency issue prevents you from starting InnoDB, see Section 14.19.2, “Forcing InnoDB Recovery” for information about manual recovery.

Problem with CREATE TABLE

A symptom of an out-of-sync data dictionary is that a CREATE TABLE statement fails. If this occurs, look in the server's error log. If the log says that the table already exists inside the InnoDB internal data dictionary, you have an orphaned table inside the InnoDB tablespace files that has no corresponding .frm file. The error message looks like this:

InnoDB: Error: table test/parent already exists in InnoDB internal
InnoDB: data dictionary. Have you deleted the .frm file
InnoDB: and not used DROP TABLE? Have you used DROP DATABASE
InnoDB: for InnoDB tables in MySQL version <= 3.23.43?
InnoDB: See the Restrictions section of the InnoDB manual.
InnoDB: You can drop the orphaned table inside InnoDB by
InnoDB: creating an InnoDB table with the same name in another
InnoDB: database and moving the .frm file to the current database.
InnoDB: Then MySQL thinks the table exists, and DROP TABLE will
InnoDB: succeed.

You can drop the orphaned table by following the instructions given in the error message. If you are still unable to use DROP TABLE successfully, the problem may be due to name completion in the mysql client. To work around this problem, start the mysql client with the --skip-auto-rehash option and try DROP TABLE again. (With name completion on, mysql tries to construct a list of table names, which fails when a problem such as just described exists.)

Problem Opening Table

Another symptom of an out-of-sync data dictionary is that MySQL prints an error that it cannot open a .InnoDB file:

ERROR 1016: Can't open file: 'child2.InnoDB'. (errno: 1)

In the error log you can find a message like this:

InnoDB: Cannot find table test/child2 from the internal data dictionary
InnoDB: of InnoDB though the .frm file for the table exists. Maybe you
InnoDB: have deleted and recreated InnoDB data files but have forgotten
InnoDB: to delete the corresponding .frm files of InnoDB tables?

This means that there is an orphaned .frm file without a corresponding table inside InnoDB. You can drop the orphaned .frm file by deleting it manually.

Orphaned Intermediate Tables

If MySQL crashes in the middle of an ALTER TABLE operation, you may be left with an orphaned intermediate table. Intermediate table names begin with #sql-. In your data directory you will see an #sql-*.ibd file and possibly an accompanying #sql-*.frm file. The intermediate table is also listed in Table Monitor output and referenced in InnoDB INFORMATION_SCHEMA tables.

Removing an orphaned intermediate table requires a table format file (a .frm file) that matches the table schema defined in the #sql-*.ibd file (it must have the same columns and indexes). Depending on when the crash occurred during the ALTER TABLE operation, the orphaned #sql-*.ibd file could have a pre-ALTER or post-ALTER schema definition, and the data in the accompanying #sql-*.frm file (if present) may or may not match.

To remove the orphaned intermediate table, perform the following steps:

  1. Determine if the #sql-*.ibd file has a pre-ALTER or post-ALTER schema definition. You can view the columns and indexes of the intermediate table using the Table Monitor or by querying InnoDB INFORMATION_SCHEMA tables. INNODB_SYS_TABLES provides the TABLE_ID for the intermediate table, which you can use to retrieve column and index information from INNODB_SYS_COLUMNS, and INNODB_SYS_INDEXES.

  2. Once you have determined if the #sql-*.ibd file has a pre-ALTER or post-ALTER schema definition, create a matching #sql-*.frm file in a different database directory. For example, if an intermediate table has a post-ALTER schema definition, create an .frm file that matches the altered schema definition:

    mysql> CREATE TABLE tmp LIKE employees.salaries; ALTER TABLE tmp DROP COLUMN to_date;
    Query OK, 0 rows affected (0.02 sec)
          
    Query OK, 0 rows affected (0.06 sec)
    Records: 0  Duplicates: 0  Warnings: 0    
  3. Copy the .frm file to the database directory where the orphaned table is located and rename it to match the name of the #sql-*.ibd file

    shell> cp tmp.frm employees/#sql-ib87.frm
  4. Drop the intermediate table by issuing a DROP TABLE statement, prefixing the name of the table with #mysql50# and enclosing the table name in backticks. For example:

    mysql> DROP TABLE `#mysql50##sql-ib87`;
    Query OK, 0 rows affected (0.01 sec)

    The #mysql50# prefix tells MySQL to ignore file name safe encoding introduced in MySQL 5.1. Enclosing the table name in backticks is required to perform SQL statements on table names with special characters such as #.

  5. If there is a leftover #sql-*.frm file, drop it. MySQL reports an unknown table error, which can be ignored.

    mysql> DROP TABLE `#mysql50##sql-36ab_2`;
    ERROR 1051 (42S02): Unknown table 'employees.#mysql50##sql-36ab_2'

Problem with Missing Tablespace

With innodb_file_per_table enabled, the following message might occur if the .frm or .ibd files (or both) are missing:

InnoDB: in InnoDB data dictionary has tablespace id N,
InnoDB: but tablespace with that id or name does not exist. Have
InnoDB: you deleted or moved .ibd files?
InnoDB: This may also be a table created with CREATE TEMPORARY TABLE
InnoDB: whose .ibd and .frm files MySQL automatically removed, but the
InnoDB: table still exists in the InnoDB internal data dictionary.

If this occurs, try the following procedure to resolve the problem:

  1. Create a matching .frm file in some other database directory and copy it to the database directory where the orphan table is located.

  2. Issue DROP TABLE for the original table. That should successfully drop the table and InnoDB should print a warning to the error log that the .ibd file was missing.