These functions build the foundation for accessing Berkeley DB style databases.
This is a general abstraction layer for several file-based databases. As such, functionality is limited to a common subset of features supported by modern databases such as Sleepycat Software's DB2. (This is not to be confused with IBM's DB2 software, which is supported through the ODBC functions.)
The behaviour of various aspects depends on the implementation of the underlying database. Functions such as dba_optimize() and dba_sync() will do what they promise for one database and will do nothing for others. You have to download and install supported dba-Handlers.
Table 1. List of DBA handlers
|dbm||Dbm is the oldest (original) type of Berkeley DB style databases. You should avoid it, if possible. We do not support the compatibility functions built into DB2 and gdbm, because they are only compatible on the source code level, but cannot handle the original dbm format.|
|ndbm||Ndbm is a newer type and more flexible than dbm. It still has most of the arbitrary limits of dbm (therefore it is deprecated).|
|gdbm||Gdbm is the GNU database manager.|
|db2||DB2 is Sleepycat Software's DB2. It is described as "a programmatic toolkit that provides high-performance built-in database support for both standalone and client/server applications.|
|db3||DB3 is Sleepycat Software's DB3.|
|db4||DB4 is Sleepycat Software's DB4. This is available since PHP 4.3.2.|
|cdb||Cdb is "a fast, reliable, lightweight package for creating and reading constant databases." It is from the author of qmail and can be found at http://cr.yp.to/cdb.html. Since it is constant, we support only reading operations. And since PHP 4.3.0 we support writing (not updating) through the internal cdb library.|
|cdb_make||Since PHP 4.3.0 we support creation (not updating) of cdb files when the bundled cdb library is used.|
|flatfile||This is available since PHP 4.3.0 for compatibility with the deprecated dbm extension only and should be avoided. However you may use this where files were created in this format. That happens when configure could not find any external library.|
|inifile||This is available since PHP 4.3.3 to be able to modify php.ini files from within PHP scripts. When working with ini files you can pass arrays of the form array(0=>group,1=>value_name) or strings of the form "[group]value_name" where group is optional. As the functions dba_firstkey() and dba_nextkey() return string representations of the key there is a new function dba_key_split() available since PHP 5 which allows to convert the string keys into array keys without loosing FALSE.|
|qdbm||This is available since PHP 5.0.0. The qdbm library can be loaded from http://qdbm.sourceforge.net.|
When invoking the dba_open() or dba_popen() functions, one of the handler names must be supplied as an argument. The actually available list of handlers is displayed by invoking phpinfo() or dba_handlers().
By using the --enable-dba=shared configuration option you can build a dynamic loadable module to enable PHP for basic support of dbm-style databases. You also have to add support for at least one of the following handlers by specifying the --with-XXXX configure switch to your PHP configure line.
After configuring and compiling PHP you must execute the following test from commandline: php run-tests.php ext/dba. This shows whether your combination of handlers works. Most problematic are dbm and ndbm which conflict with many installations. The reason for this is that on several systems these libraries are part of more than one other library. The configuration test only prevents you from configuring malfaunctioning single handlers but not combinations.
Table 2. Supported DBA handlers
To enable support for dbm add
To enable support for ndbm add
|gdbm||To enable support for gdbm add --with-gdbm[=DIR].|
To enable support for db2 add
To enable support for db3 add
To enable support for db4 add
To enable support for cdb add
To enable support for flatfile add
To enable support for inifile add
To enable support for qdbm add
Note: Up to PHP 4.3.0 you are able to add both db2 and db3 handler but only one of them can be used internally. That means that you cannot have both file formats. Starting with PHP 5.0.0 there is a configuration check avoid such missconfigurations.
DBA is binary safe and does not have any arbitrary limits. However, it inherits all limits set by the underlying database implementation.
All file-based databases must provide a way of setting the file mode of a new created database, if that is possible at all. The file mode is commonly passed as the fourth argument to dba_open() or dba_popen().
Example 2. Traversing a database