14.22 InnoDB Limits

This section describes limits for InnoDB tables, indexes, tablespaces, and other aspects of the InnoDB storage engine.

• A table can contain a maximum of 1017 columns (raised in MySQL 5.6.9 from the earlier limit of 1000).

• A table can contain a maximum of 64 secondary indexes.

• By default, the index key prefix length limit is 767 bytes. See Section 13.1.13, “CREATE INDEX Statement”. For example, you might hit this limit with a column prefix index of more than 255 characters on a TEXT or VARCHAR column, assuming a utf8mb3 character set and the maximum of 3 bytes for each character. When the innodb_large_prefix configuration option is enabled, the index key prefix length limit is raised to 3072 bytes for InnoDB tables that use the DYNAMIC or COMPRESSED row format.

  Attempting to use an index key prefix length that exceeds the limit returns an error. To avoid such errors in replication configurations, avoid enabling innodb_large_prefix on the source if it cannot also be enabled on replicas.

  If you reduce the InnoDB page size to 8KB or 4KB by specifying the innodb_page_size option when creating the MySQL instance, the maximum length of the index key is lowered proportionally, based on the limit of 3072 bytes for a 16KB page size. That is, the maximum index key length is 1536 bytes when the page size is 8KB, and 768 bytes when the page size is 4KB.

  The limits that apply to index key prefixes also apply to full-column index keys.

• A maximum of 16 columns is permitted for multicolumn indexes. Exceeding the limit returns an error.

  ERROR 1070 (42000): Too many key parts specified; max 16 parts allowed

• The maximum row size, excluding any variable-length columns that are stored off-page, is slightly less than half of a page. That is, the maximum row size is about 8000 bytes for the default page size of 16KB. If you reduce the page size by specifying the innodb_page_size option when creating the MySQL instance, the maximum row size is 4000 bytes for 8KB pages, or 2000 bytes for 4KB pages. LONGBLOB and LONGTEXT columns must be less than 4GB, and the total row size, including BLOB and TEXT columns must be less than 4GB.

  If a row is less than half a page long, all of it is stored locally within the page. If it exceeds half a page, variable-length columns are chosen for external off-page storage until the row fits within half a page, as described in Section 14.12.2, “File Space Management”.

• Although InnoDB supports row sizes larger than 65,535 bytes internally, MySQL itself imposes a row-size limit of 65,535 for the combined size of all columns. See Section 8.4.7, “Limits on Table Column Count and Row Size”.

• On some older operating systems, files must be less than 2GB. This is not an InnoDB limitation. If you require a large system tablespace, configure it using several smaller data files rather than one large data file, or distribute table data across file-per-table data files.

• The combined maximum size for InnoDB log files is 512GB.

• The minimum tablespace size is slightly larger than 10MB. The maximum tablespace size depends on the InnoDB page size.

  Table 14.20 InnoDB Maximum Tablespace Size

  InnoDB Page Size	Maximum Tablespace Size
  4KB	16TB
  8KB	32TB
  16KB	64TB

  
  

  The maximum tablespace size is also the maximum size for a table.

• Tablespace files cannot exceed 4GB on Windows 32-bit systems (Bug #80149).

• The path of a tablespace file, including the file name, cannot exceed the MAX_PATH limit on Windows. Prior to Windows 10, the MAX_PATH limit is 260 characters. As of Windows 10, version 1607, MAX_PATH limitations are removed from common Win32 file and directory functions, but you must enable the new behavior.

• For limits associated with concurrent read-write transactions, see Section 14.6.7, “Undo Logs”.