Databases - Firebird

Each database exists in one or more files, which grow dynamically as the need arises. Database files must be stored on disk storage that is under the physical control of the machine on which the server is hosted. Only a server process can perform direct I/O on the database files.

A Firebird database file consists of blocks of storage known as pages. The size of one database page can be 1K, 2K, 4K, 8K, or 16K, and it is set at database creation time. It can be changed only by restoring a backed-up database and specifying a new size. Different databases on the same server can have different page sizes.

The server maintains a number of different page types in each database —data pages, several levels of index pages, BLOB pages, inventory pages for various accounting purposes, and so on. It lays out pages in a geography known only to itself and a handful of gifted wizards. Unlike file-served DBMSs, Firebird does not store tables in physical rows and columns but in a continuous stream, on pages. When a page is nearing full capacity and more rows are to be written, the server allocates a new page. Pages from a single table are not stored in any contiguous sequence. In fact, pages belonging to a single table could be distributed across several files on several disks.

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