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2.12.2 Downgrading MySQL »
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2.12.1.2. Upgrading from MySQL 5.4 to 5.5

Note

It is good practice to back up your data before installing any new version of software. Although MySQL works very hard to ensure a high level of quality, you should protect your data by making a backup.

To upgrade to 5.5 from any previous version, MySQL recommends that you dump your tables with mysqldump before upgrading and reload the dump file after upgrading.

In general, you should do the following when upgrading from MySQL 5.4 to 5.5:

  • Read all the items in the following sections to see whether any of them might affect your applications:

    Note particularly any changes that are marked Known issue or Incompatible change. These incompatibilities with earlier versions of MySQL may require your attention before you upgrade. Our aim is to avoid these changes, but occasionally they are necessary to correct problems that would be worse than an incompatibility between releases. If any upgrade issue applicable to your installation involves an incompatibility that requires special handling, follow the instructions given in the incompatibility description. Often this will involve dumping and reloading tables, or use of a statement such as CHECK TABLE or REPAIR TABLE.

    For dump and reload instructions, see Section 2.12.4, “Rebuilding or Repairing Tables or Indexes”. Any procedure that involves REPAIR TABLE with the USE_FRM option must be done before upgrading. Use of this statement with a version of MySQL different from the one used to create the table (that is, using it after upgrading) may damage the table. See Section 12.4.2.5, “REPAIR TABLE Syntax”.

  • Before upgrading to a new version of MySQL, Section 2.12.3, “Checking Whether Tables or Indexes Must Be Rebuilt”, to see whether changes to table formats or to character sets or collations were made between your current version of MySQL and the version to which you are upgrading. If so and these changes result in an incompatibility between MySQL versions, you will need to upgrade the affected tables using the instructions in Section 2.12.4, “Rebuilding or Repairing Tables or Indexes”.

  • After upgrading to a new version of MySQL, run mysql_upgrade (see Section 4.4.7, “mysql_upgrade — Check Tables for MySQL Upgrade”). This program checks your tables, and attempts to repair them if necessary. It also updates your grant tables to make sure that they have the current structure so that you can take advantage of any new capabilities. (Some releases of MySQL introduce changes to the structure of the grant tables to add new privileges or features.)

  • If you run MySQL Server on Windows, see Section 2.3.14, “Upgrading MySQL on Windows”.

  • If you use replication, see Section 16.4.3, “Upgrading a Replication Setup”, for information on upgrading your replication setup.

If your MySQL installation contains a large amount of data that might take a long time to convert after an in-place upgrade, you might find it useful to create a “dummy” database instance for assessing what conversions might be needed and the work involved to perform them. Make a copy of your MySQL instance that contains a full copy of the mysql database, plus all other databases without data. Run your upgrade procedure on this dummy instance to see what actions might be needed so that you can better evaluate the work involved when performing actual data conversion on your original database instance.

MySQL Enterprise.  MySQL Enterprise subscribers will find more information about upgrading in the Knowledge Base articles found at Upgrading. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

The following lists describe changes that may affect applications and that you should watch out for when upgrading from MySQL 5.4 to 5.5.

Configuration Changes:

  • Incompatible change: In MySQL 5.5, the server includes a plugin services interface that complements the plugin API. The services interface enables server functionality to be exposed as a “service” that plugins can access through a function-call interface. The libmysqlservices library provides access to the available services and dynamic plugins now must be linked against this library (use the -lmysqlservices flag). For an example showing what Makefile.am should look like, see Section 22.2.6, “MySQL Services for Plugins”.

Server Changes:

  • Incompatible change: As of MySQL 5.5.3, the Unicode implementation has been extended to provide support for supplementary characters that lie outside the Basic Multilingual Plane (BMP). Noteworthy features:

    • utf16 and utf32 character sets have been added. These correspond to the UTF-16 and UTF-32 encodings of the Unicode character set, and they both support supplementary characters.

    • The utf8mb4 character set has been added. This is similar to utf8, but its encoding allows up to four bytes per character to enable support for supplementary characters.

    • The ucs2 character set is essentially unchanged except for the inclusion of some newer BMP characters.

    In most respects, upgrading to MySQL 5.5 should present few problems with regard to Unicode usage, although there are some potential areas of incompatibility. These are the primary areas of concern:

    • For the variable-length character data types (VARCHAR and the TEXT types), the maximum length in characters is less for utf8mb4 columns than for utf8 columns.

    • For all character data types (CHAR, VARCHAR, and the TEXT types), the maximum number of characters that can be indexed is less for utf8mb4 columns than for utf8 columns.

    Consequently, if you want to upgrade tables from utf8 to utf8mb4 to take advantage of supplementary-character support, it may be necessary to change some column or index definitions.

    For additional details about the new Unicode character sets and potential incompatibilities, see Section 9.1.10, “Unicode Support”, and Section 9.1.11, “Upgrading from Previous to Current Unicode Support”.

  • Incompatible change: As of MySQL 5.5.3, the server includes dtoa, a library for conversion between strings and numbers by David M. Gay. In MySQL, this library provides the basis for improved conversion between string or DECIMAL values and approximate-value (FLOAT/DOUBLE) numbers.

    Because the conversions produced by this library differ in some cases from previous results, the potential exists for incompatibilities in applications that rely on previous results. For example, applications that depend on a specific exact result from previous conversions might need adjustment to accommodate additional precision.

    For additional information about the properties of dtoa conversions, see Section 11.2.2, “Type Conversion in Expression Evaluation”.

  • Incompatible change: In MySQL 5.5, several changes were made regarding the language and character set of error messages:

    • The --language option for specifying the directory for the error message file is now deprecated. The new --lc-messages-dir and --lc-messages options should be used instead, and --language is handled as an alias for --lc-messages-dir.

    • The language system variable has been removed and replaced with the new lc_messages_dir and lc_messages system variables. lc_messages_dir has only a global value and is read only. lc_messages has global and session values and can be modified at runtime, so the error message language can be changed while the server is running, and individual clients each can have a different error message language by changing their session lc_messages value to a different locale name.

    • Error messages previously were constructed in a mix of character sets. This issue is resolved by constructing error messages internally within the server using UTF-8 and returning them to the client in the character set specified by the character_set_results system variable. The content of error messages therefore may in some cases differ from the messags returned previously.

    For more information, see Section 9.2, “Setting the Error Message Language”, and Section 9.1.6, “Character Set for Error Messages”.

SQL Changes: