I use PHP4.0.3pl1 in my test environment and PHP3.0.16 in the production environment.
While making multiple connections to Sybase (Open Client version 11.9.2)
with the same arguments, PHP3 returns always the same link identifier but PHP4 not.
It seems that PHP4 makes new connections when calling sybase_connect() repeatedly.

Here is my PHP script:
<?php
$conn = sybase_connect("SYBASE", "username", "passwd"); echo $conn."<br>";
$conn = sybase_connect("SYBASE", "username", "passwd"); echo $conn."<br>";
$conn = sybase_connect("SYBASE", "username", "passwd"); echo $conn."<br>";
$conn = sybase_connect("SYBASE", "username", "passwd"); echo $conn."<br>";
$conn = sybase_connect("SYBASE", "username", "passwd"); echo $conn."<br>";
$conn = sybase_connect("SYBASE", "username", "passwd"); echo $conn."<br>";
$conn = sybase_connect("SYBASE", "username", "passwd"); echo $conn."<br>";
$conn = sybase_connect("SYBASE", "username", "passwd"); echo $conn."<br>";
$conn = sybase_connect("SYBASE", "username", "passwd"); echo $conn."<br>";
$conn = sybase_connect("SYBASE", "username", "passwd"); echo $conn."<br>";
?>

The results are the followings:
PHP3:
1
1
1
1
1
1
1
1
1
1

PHP4:
Resource id #1
Resource id #1
Resource id #1
Resource id #1
Resource id #1
Resource id #2
Resource id #2
Resource id #2
Resource id #2
Resource id #3

The configure line for PHP4 is:
./configure --with-apache=../apache \
	--with-config-file-path=/usr/local/apache/etc \
	--with-sybase-ct=/sybase --with-sybase-db=/sybase \
	--with-oci8 --with-oracle \
	--with-gdbm --with-gd --with-pdflib --with-zlib \
	--with-jpeg-dir=/usr/local --with-tiff-dir=/usr/local \
	--enable-calendar --enable-dbase --enable-yp \
	--enable-versioning --enable-track-vars --enable-ftp \
	--enable-trans-sid --enable-sysvsem --enable-sysvshm

The web server is Apache 1.3.12 running on Solaris 2.6.
The compiler is GNU gcc 2.95.2.