Programming the Perl DBI

Creating a New Database

Prior to manipulating data within a Berkeley database, either a new database must be created or an existing database must be opened for reading. This can be done by using one of the following function calls:

tie %hash,  'DB_File', $filename, $flags, $mode, $DB_HASH;
tie %hash,  'DB_File', $filename, $flags, $mode, $DB_BTREE;
tie @array, 'DB_File', $filename, $flags, $mode, $DB_RECNO;

The final parameter of this call is the interesting one, as it dictates the way in which the Berkeley DB will store the data in the database file. The behavior of these parameters is as follows:

• DB_HASH is the default behavior for Berkeley DB databases. It stores the data according to a hash value computed from the string specified as the key itself. Hashtables are generally extremely fast, in that by simply applying the hash function to any given key value, the data associated with that key can be located in a single operation. This is much faster than sequential scanning. However, hashtables provide no useful ordering of the data by default, and hashtable performance can begin to degrade when several keys have identical hash key values. This results in several items of data being attached to the same hash key value, which results in slower access times.

• With the DB_BTREE format, Berkeley DB files are stored in the form of a balanced binary tree. The B-tree storage technique will sort the keys that you insert into the Berkeley DB, the default being to sort them in lexical order. ...