OCIServerAttach() is used, implying that the module should take advantage of shared data mode, but OCIInitilize() was not passed SHARED_MODE flag (#define PHP_OCI_INIT_MODE OCI_DEFAULT), so I don't believe it's really taking advantage of shared data mode.  Excerpt from OCI8 docs:

<code>
To trigger OCI shared mode functionality, process handle parameters must be set and OCIInitialize() must be called with the mode flag set to OCI_SHARED. For example: 

ub4 mode = OCI_SHARED | OCI_THREADED;
OCIInitialize (mode, 0, 0, 0, 0);

The first application that initializes OCI in shared mode starts up the shared subsystem using the parameters set by that OCI application. When subsequent applications initialize using the shared mode, they use the previously started shared subsystem.
</code>

Using this should reduce memory usage when large number of simultaneous connections are open and large numbers of concurrent statements (differing only by bind values) are running.

ref: http://www.csee.umbc.edu/help/oracle8/server.815/a67846/basics.htm#425685