There are a number of PostgreSQL-related PHP functions that I have not covered in this chapter.
Newer versions of PHP have added support for asynchronous query processing (see pg_send_query(), pg_connection_busy(), and pg_get_result()). Asynchronous query processing probably won't be of much use when you are constructing dynamic web pages, but clever coders can use asynchronous queries to provide intermediate feedback for long-running operations (sorry, I'm not that clever).
PHP offers a set of functions that can give you information about a database connection. We used the pg_dbname() function in the first client (see Listing 15.4) to display the name of the database to which we were connected. You can also use the pg_port()and pg_options() function to retrieve the port number and options associated with a database connection. PHP provides a pg_host() function that is supposed to return the name of the host where the server resides. Be very careful calling pg_host(); if you have established a local connection (that is, using a Unix-domain socket), calling pg_host() may crash your web server because of a bug in the PHP/PostgreSQL interface.
Another function offered by PHP is pg_pconnect(). The pg_pconnect() function establishes a persistent connection to a PostgreSQL database. Persistent connections are cached by the web server and can be reused the next time a browser requests a document that requires access to the same database. See the PHP manual for information about the pros and cons of persistent connections.
Finally, PHP supports the PostgreSQL large-object interface. You can use the large-object interface to read (or write) large data items such as images or audio files.