Early versions of
InnoDB used an unnamed file
format (now called Antelope)
for database files. With that file format, tables are defined with
ROW_FORMAT=REDUNDANT. With these row formats,
InnoDB stores up to the first 768 bytes of
variable-length columns (
TEXT types) in the index record
within the B-tree node, with
the remainder stored on the overflow pages.
InnoDB also encodes fixed-length fields greater
than or equal to 768 bytes in length as variable-length fields,
which can be stored off-page. For example, a
CHAR(255) column can exceed 768 bytes if the
maximum byte length of the character set is greater than 3, as it
With the Antelope file format, if the value of a column is 768
bytes or less, 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
BLOBs, but may cause
B-tree nodes to fill with data rather than key values, reducing
their efficiency. Tables with many
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.
To preserve compatibility with prior versions of
created in MySQL 5.5 default to the
COMPACT row format rather than the newer
DYNAMIC row format. See
Section 14.14.3, “DYNAMIC and COMPRESSED Row Formats” for more information.
For information about the physical row structure of tables that
row format, see Section 126.96.36.199, “The Physical Row Structure of an InnoDB Table”.