What is Page?
Both on disk and in memory, database data is stored as a consecutive byte blocks with same size. Each block is called a page. Normal page size are 4KB, 8KB, 16KB bytes. Data I/O operation is performed on the unit of pages. Most of the time, database can't hold all data in the memory, thus it employs a buffer pool to maintain a list of active pages based on LRU. The buffer pool swaps the pages continuously based on the access pattern, a process known as page-in, page-out.