How InnoDB Handles TEXT/BLOB Columns
Recently we had a debate in the consulting team about how InnoDB handles TEXT/BLOB columns. More specifically, the argument was around the Barracuda file format with dynamic rows.
When a table is created with ROW_FORMAT=DYNAMIC, InnoDB can store long variable-length column values (for VARCHAR, VARBINARY, and BLOB and TEXT types) fully off-page, with the clustered index record containing only a 20-byte pointer to the overflow page. … Whether columns are stored off-page depends on the page size and the total size of the row. When a row is too long, the longest columns are chosen for off-page storage until the clustered index record fits on the B-tree page. TEXT and BLOB columns that are less than or equal to 40 bytes are stored in line.
The first paragraph indicates InnoDB can store long columns fully off-page, in an overflow page. A little further down in the documentation, the behavior of short values, the ones with lengths less than 40 bytes, is described. These short values are stored in the row.
