Sorry, but your problem does not imply a bug in PHP itself.  For a
list of more appropriate places to ask for help using PHP, please
visit http://www.php.net/support.php as this bug system is not the
appropriate forum for asking support questions. 

Thank you for your interest in PHP.

MySQL is designed for speed DB2 is designed for scalability & large applications where stability & data integerity is more important then speed. Hence the difference you are seeing, as is this is NOT a php bug or even a PHP related issue.

Just to answer this a bit further.  DB2 uses ODBC as it's native system, MySQL uses a private/custom interface.  When one can optimize for speed to a single protocol, DB2 worries about all protocols.  It's going to be slower no matter what you do.

This may be useful - From UnixODBC 2.2.0 Doco

Another useful hint. Somewho has been using PHP+DB2 on AIX via unixODBC to a BIG IBM server (4 processors, bags of core etc), and finding it was slow. It turns out there is a bug
in IBM's TCP/IP stack. after looking at this and setting this 

$ su - db2inst1
$ db2set DB2TCPCONNMGRS=1

To quote "... the difference was UNBELIEVABLE !!!". Thanks Eric. 


"This" is the following link http://www-4.ibm.com/cgi-bin/db2www/data/db2/udb/winos2unix/support/document.d2w/report?last_page=list.d2w&fn=1006553

Remember - DB2 is a lot more complex than MySQL, and diagnosing issues is not as simple as saying "it's slow". That's why there are highly paid DBA's!

Additionally there's no information in this bug report about whether the DB2 DB is on the same box, load, versions, what's been attepmpted or any other information that could be remotely useful.