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A multi-file database consists of a primary file and one or more secondary files. You can create one or more secondary files to be used for overflow purposes only; you cannot specify what information goes into each file because InterBase handles this automatically. Each secondary file is typically assigned to a different disk than that of the main database. When the primary file fills up, InterBase allocates one of the secondary files that was created. When that secondary file fills up, another secondary file is allocated, and so on, until all of the secondary file allocations run out.
Whenever possible, the database should be created locally; create the database on the same machine where you are running ISQL. If the database is created locally, secondary file names can include a full file specification, including both host or node names, and a directory path to the location of the database file. If the database is created on a remote server, secondary file specifications cannot include a node name, as all secondary files must reside on the same node.

Specifying file size of a secondary file

Unlike primary files, when you define a secondary file, you must declare either a file length in pages, or a starting page number. The LENGTH parameter specifies a database file size in pages.
If you choose to describe page ranges in terms of length, list the files in the order in which they should be filled. The following example creates a database that is stored in four 10,000-page files, Starting with page 10,001, the files are filled in the order employee.gdb, employee.gd1, employee.gd2, and employee.gd3.

CREATE DATABASE "employee.gdb"
FILE "employee.gd1" STARTING AT PAGE 10001
LENGTH 10000 PAGES
FILE "employee.gd2"
LENGTH 10000 PAGES
FILE "employee.gd3"
LENGTH 10000 PAGES;

Note: Because file-naming conventions are platform-specific, for the sake of simplicity, none of the examples provided include the device and path name portions of the file specification.

When the last secondary file fills up, InterBase automatically extends the file beyond the LENGTH limit until its disk space runs out. You can either specify secondary files when the database is defined, or add them later, as they become necessary, using ALTER DATABASE. Defining secondary files when a database is created immediately reserves disk space for the database.

Specifying the starting page number of a secondary file

If you do not declare a length for a secondary file, then you must specify a starting page number. STARTING AT PAGE specifies the beginning page number for a secondary file.

The primary file specification in a multi-file database does not need to include a length, but secondary file specifications must then include a starting page number. You can specify a combination of length and starting page numbers for secondary files.

InterBase overrides a secondary file length that is inconsistent with the starting page number. In the next example, the primary file is 10,000 pages long, but the first secondary file starts at page 5,000:

CREATE DATABASE "employee.gdb" LENGTH 10000
FILE "employee.gd1" STARTING AT PAGE 5000
LENGTH 10000 PAGES
FILE "employee.gd2"
LENGTH 10000 PAGES
FILE "employee.gd3";

InterBase generates a primary file that is 10,000 pages long, starting the first secondary file at page 10,001.

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