InnoDB in MySQL 5.5 contains several important new features:
Performance and scalability enhancements:
Asynchronous I/O is supported on Linux systems. For additional information, see
Improvements to crash recovery performance, as described in Section 8.5.8, “Optimizing InnoDB Configuration Variables”.
An increased limit on concurrent data modifying transactions, as described in Section 14.5.4, “InnoDB Rollback Segments”.
Other changes for flexibility, ease of use and reliability:
The Barracuda File Format. See Section 14.11, “InnoDB File-Format Management”.
InnoDBStrict Mode. For usage information, refer to the
More compact output for
SHOW ENGINE INNODB MUTEX. For more information see, Section 184.108.40.206, “SHOW ENGINE Syntax”.
SHOW ENGINE INNODB STATUSoutput displays counter information for the
Innodb_buffer_pool_read_ahead_evictedglobal status variables, which can help you fine-tune the
innodb_random_read_aheadsetting and evaluate the effectiveness of the read-ahead algorithm.
Note that the ability to use data compression and the new row format require the use of a new InnoDB file format called Barracuda. The previous file format, used by the built-in InnoDB in MySQL 5.1 and earlier, is now called Antelope and does not support these features, but does support the other features introduced with the InnoDB storage engine.
The InnoDB storage engine is upward compatible from standard InnoDB as
built in to, and distributed with, MySQL. Existing databases can
be used with the InnoDB Storage Engine for MySQL. The new parameter
innodb_file_format can help
protect upward and downward compatibility between InnoDB versions
and database files, allowing users to enable or disable use of new
features that can only be used with certain versions of InnoDB.
InnoDB since version 5.0.21 has a safety feature that prevents it from opening tables that are in an unknown format. However, the system tablespace may contain references to new-format tables that confuse the built-in InnoDB in MySQL 5.1 and earlier. These references are cleared in a slow shutdown.
With previous versions of InnoDB, no error would be returned until you try to access a table that is in a format “too new” for the software. To provide early feedback, InnoDB 1.1 checks the system tablespace before startup to ensure that the file format used in the database is supported by the storage engine. See Section 220.127.116.11, “Compatibility Check When InnoDB Is Started” for the details.