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,
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.
Changing the 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
A MySQL instance using a particular
page size cannot use data files or log files from an instance
that uses a different page size.