InnoDB indexes are
B-trees where the index
records are stored in the leaf pages of the tree. The default
size of an index page is 16KB.
When new records are inserted into an
InnoDB tries to leave 1/16 of the page free
for future insertions and updates of the index records. If index
records are inserted in a sequential order (ascending or
descending), the resulting index pages are about 15/16 full. If
records are inserted in a random order, the pages are from 1/2
to 15/16 full. If the fill
factor of an index page drops below 1/2,
InnoDB tries to contract the index tree to
free the page.
InnoDB page size is not a
supported operation and there is no guarantee that
InnoDB will function normally with a page
size other than 16KB. Problems compiling or running
InnoDB may occur. In particular,
ROW_FORMAT=COMPRESSED in the Barracuda file
format assumes that the page size is at most 16KB and uses
An instance using a particular
size cannot use data files or log files from an instance that
uses a different page size.