*** A note about pthreads ***
The db4 c++ library by default tries to link against libpthread on some
systems (notably Linux).  If your PHP install is not linked against
libpthread, you will need to disable pthread support in db4.  This can
be done by compiling db4 with the flag  --with-mutex=x86/gcc-assembly.
PHP can itself be forced to link against libpthread either by manually
editing
its build files (which some distributions do), or by building it with
--with-experimental-zts.

This module requires that Berkeley DB be configured and built using 
--enable-cxx to enable C++. To install this php module execute the following 
steps:

> phpize
> ./configure --with-db4[=/path/to/db4]
> make
> su -
# make install

Then in your php.ini file add this line:

extension=db4.so

See examples in the "samples" directory.  The samples run in /var/tmp and the
transaction_counter.php example requires that /var/tmp/dbhome exist. The 
samples can be edited to change these requirements.