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Backward Compatibility

Considerations of backward compatibility only apply when using a recent version of InnoDB (the

InnoDB Plugin, or MySQL 5.5 and higher with InnoDB 1.1) alongside an older one (MySQL 5.1 or

earlier, with the built-in InnoDB rather than the InnoDB Plugin). To minimize the chance of compatibility

issues, you can standardize on the InnoDB Plugin for all your MySQL 5.1 and earlier database servers.

In generał, a newer version of InnoDB may create a table or index that cannot safely be read or written

with a prior version of InnoDB without risk of crashes, hangs, wrong results or corruptions. InnoDB 1.1

includes a mechanism to guard against these conditions, and to help preserve compatibility among

database files and versions of InnoDB. This mechanism lets you take advantage of some new features

of an InnoDB release (such as performance improvements and bug fixes), and still preserve the option

of using your database with a prior version of InnoDB, by preventing

accidental use of new features

that create downward-incompatible disk files.

If a version of InnoDB supports a particular file format (whether or not that format is the default), you

can query and update any table that requires that format or an earlier format. Only the creation of

new tables using new features is limited based on the particular file format enabled. Conversely, if

a tablespace contains a table or index that uses a file format that is not supported by the currently

running software, it cannot be accessed at all, even for read access.

The only way to “downgrade” an InnoDB tablespace to an earlier file format is to copy the data to a new

table, in a tablespace that uses the earlier format. This can be done with the alter table statement,

as described in Section 5.4.7.4, “Downgrading the File Format".

The easiest way to determine the file format of an existing InnoDB tablespace is to examine the

properties of the table it contains, using the show table status command or querying the table

INFORMATION_SCHEMA.TABLES. If the Row_format of the table is reported as 'Compressed'