Using PostGres 7.0.2, and the latest PHP, any script that
would choose to open a database connection a second time
will fail.

For example:

<?
        $pg = pg_connect("dbname=customer");
        $res  = pg_exec("select count(*) from list_weeklynews;");
        pg_close($pg);

        $pg = pg_connect("dbname=customer");
        $res  = pg_exec("select count(*) from list_weeklynews;");
        pg_close($pg);
?>

The second connect fails with:

1 is not a valid PostgreSQL link resource in file.php

Repeating the 3 lines multiple times in the script does pretty
unusual stuff - the file descriptor is bouncing all over the place -
if file descriptors were properly closed, the same descriptor
would in all likelihood be re-used