Programming the Perl DBI

DBM Files and the BerkeleyDatabase Manager

DBM files are a storage management layer that allows programmers to store information in files as pairs of strings, a key, and a value. DBM files are binary files and the key and value strings can also hold binary data.

There are several forms of DBM files, each with its own strengths and weaknesses. Perl supports the ndbm , db , gdbm , sdbm , and odbm managers via the NDBM_File , DB_File , GDBM_File , SDBM_File , and ODBM_File extensions. There’s also an AnyDBM_File module that will simply use the best available DBM. The documentation for the AnyDBM_File module includes a useful table comparing the different DBMs.

These extensions all associate a DBM file on disk with a Perl hash variable (or associative array ) in memory.^[13] The simple look like a hash programming interface lets programmers store data in operating system files without having to consider how it’s done. It just works.

Programmers store and fetch values into and out of the hash, and the underlying DBM storage management layer will look after getting them on and off the disk.

In this section, we shall discuss the most popular and sophisticated of these storage managers, the Berkeley Database Manager, also known as the Berkeley DB. This software is accessed from Perl via the DB_File and Berkeley DB extensions. On Windows systems, it can be installed via the Perl package manager, ppm. On Unix systems, it is built by default when Perl is built only if the Berkeley DB library ...