Compiling php with modules vs using shared modules?

Question

Is there a difference between compiling php with the parameter:

--with-[extension name]

as opposed to just compiling it as a shared module and including it that way? Is there any performance benefit? If not, why would you want to do this?

Answer 1

Hi,

Maybe it won't be a full answer to your question, but here's what I've been able to find so far : there is some kind of a partial answer in the book "Extending and Embedding PHP", written by Sara Golemon (amazon ; some parts are also available on google books).

The relevant part (a note at the top of page 56) is :

Ever wonder why some extensions are configured using --enable-extname and some are configured using --with-extename? Functionnaly, there is no difference between the two. In practice, however, --enable is meant for features that can be turned on witout requiring any third-party libraries. --with, by contrast, is meant for features that do have such prerequisites.

So, not a single word about performance (I guess, if there is a difference, it is only a matter of "loading one more file" vs "loading one bigger file") ; but there is a technical reason behind this possibility.

I guess this is done so PHP itself doesn't require an additionnal external library because of some extension ; using the right option allows for users to enable or disable the extension themselves, depending on whether or not they already have that external library.

Answer 2

Any performance benefit would be negligible. It’s simply another option for packaging up your PHP build.

On my Mac I use Marc Liyange’s build of PHP, which includes, among other things, built-in PostgreSQL support. It was built with the --with-pdo-pgsql flag. As a result it does not need to be distributed with the pdo-pgsql shared library.

If he did not build with --with-pdo-pgsql, he would have needed to distribute the pdo-pgsql shared library and include a directive in php.ini to load it. Sure, it’s just a minor difference, but if you know you are going to be using that functionality, it’s fine to build it into PHP itself.

Answer 3

Hi,

I guess Nate is right about the performance and that this options only help for packing.

Basically with a compiled-in module PHP can call directly the module functions, but, after the compilation, this calls are translated into memory addresses to be called.

In the loadable module version, PHP will call a dl_open to load the library and then call the functions by there addresses, juts like the compiled-in version does. I guess that this dl_open call is done only once when the webserver is started, so you can ignore it.