innodb_file_format is set to “Barracuda” and a table is
column values are stored fully off-page, and the clustered index
record contains only a 20-byte pointer to the overflow page.
Whether any columns are stored off-page depends on the page size and the total size of the row. When the row is too long, InnoDB chooses the longest columns for off-page storage until the clustered index record fits on the B-tree page.
DYNAMIC row format maintains the efficiency of storing the
entire row in the index node if it fits (as do the
REDUNDANT formats), but this new format avoids the problem of
filling B-tree nodes with a large number of data bytes of long
DYNAMIC format is predicated on the idea that if a
portion of a long data value is stored off-page, it is usually
most efficient to store all of the value off-page. With
format, shorter columns are likely to remain in the B-tree node,
minimizing the number of overflow pages needed for any given row.