Previous versions of InnoDB used an unnamed file format (now
called “Antelope”) for database files. With that format, tables
were defined with
and InnoDB stored up to the first 768 bytes of variable-length
columns (such as
VARCHAR) in the index record within the B-tree
node, with the remainder stored on the overflow page(s).
To preserve compatibility with those prior versions, tables
created with the InnoDB Plugin use the prefix format, unless one
ROW_FORMAT=COMPRESSED is specified
(or implied) on the
CREATE TABLE command.
With the “Antelope” file format, if the value of a column is not
longer than 768 bytes, no overflow page is needed, and some
savings in I/O may result, since the value is in the B-tree node.
This works well for relatively short
may cause B-tree nodes to fill with data rather than key values,
thereby reducing their efficiency. Tables with many
BLOB columns could cause B-tree nodes to become
too full of data, and contain too few rows, making the entire
index less efficient than if the rows were shorter or if the
column values were stored off-page.