The minimum page size is 512 bytes and the maximum page size is 64K bytes, and must be a power of two. First, the page size implicitly sets the size of an overflow record. Overflow records are key or data items that are too large to fit on a normal database page because of their size, and are therefore stored in overflow pages.
Overflow pages are pages that exist outside of the normal database structure.
For this reason, there is often a significant performance penalty associated with retrieving or modifying overflow records. Selecting a page size that is too small, and which forces the creation of large numbers of overflow pages, can seriously impact the performance of an application. Second, in the Btree, Hash and Recno access methods, the finest-grained lock that Berkeley DB acquires is for a page. Selecting a page size that is too large, and which causes threads or processes to wait because other threads of control are accessing or modifying records on the same page, can impact the performance of your application. Berkeley DB will give a page-sized unit of bytes to the operating system to be scheduled for writing to the disk.