Extent size
The default size for first and next extents is 16 kilobytes. If this transforms to fewer than 4 pages in a particular dbspace, the database server uses the minimum extent size of 4 pages. If a dbspace has a size of 8 kilobytes, which transforms to 2 pages, the database server increases the extent size to 32 kilobytes.
The maximum size of an extent is 2**31 pages, equivalent to the maximum chunk size.
If the chunk is smaller than the maximum size, the maximum extent size depends on the contiguous space available in the chunk.
Tblspaces that hold index fragments follow different rules for extent size. The database server bases the extent size for these tblspaces on the extent size for the corresponding table fragment. The database server uses the ratio of the row size to index key size to assign an appropriate extent size for the index tblspace (see the sections on estimating index page size and fragmenting table indexes in the Informix® Performance Guide).
The maximum number of extents for a partition is 32767.