XVI. Database (dbm-style) Abstraction Layer
Functions
Introduction
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.)
Requirements
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
Handler Notes
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().
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