What makes PHP slower than Java or C#?

Question

One reason is the lack of a JIT compiler in PHP, as others have mentioned.

Another big reason is PHP's dynamic typing. A dynamically typed language is always going to be slower than a statically typed language, because variable types are checked at run-time instead of compile-time. As a result, statically typed languages like C# and Java are going to be significantly faster at run-time, though they typically have to be compiled ahead of time. A JIT compiler makes this less of an issue for dynamically typed languages, but alas, PHP does not have one built-in. (Edit: PHP 8 will come with a built-in JIT compiler.)

I'm guessing you are a little bit into the comparing of apples and oranges here - assuming that you are using all these languages to create web applications there is quite a bit more to it than just the language. (And lots of the time it is the database that is slowing you down ;-)

I would never suggest choosing one of these languages over the other on the basis of a speed argument.

Both Java and C# have JIT compilers, which take the bytecode and compile into true machine code. The act of compiling it can take time, hence C# and Java can suffer from slower startup times, but once the code is JIT compiled, its performance is in the same ballpark as any "truly compiled" language like C++.

The biggest single reason is that Java's HotSpot JVM and C#'s CLR both use Just-In-Time (JIT) compilation. JIT compilation compiles the bytecodes down to native code that runs directly on the processor.

Also I think Java bytecode and CIL are lower-level than PHP's internal bytecode which might make alot of JIT optimizations easier and more effective.

A wild guess might be that JAVA depends on some kind of "application" server, while PHP doesn't -- which means a new environnement has to be created each time a PHP page is called.

(This was especially true when PHP was/is used as a CGI, and not as an Apache module or via FastCGI)

Another idea might be that C# and JAVA compilers can do some heavy optimisations at compile time -- on the other side, as PHP scripts are compiled (at least, if you don't "cheat" with an opcode cache) each time a page is called, the compilation phase has to be real quick ; which means it's not possible to spend much time optimizing.

Still : Each version of PHP generally comes with some amelioration of the performances ; for instance, you can gain between 15% and 25% of CPU, when switching from PHP 5.2 to 5.3.

For instance, take a look at those benchmarks :

• Benchmark of PHP Branches 3.0 through 5.3-CVS
• Performance PHP 5.2 vs PHP 5.3 - huge gain
• Bench PHP 5.2 vs PHP 5.3 -- disclaimer : it's in french, and I'm the one who did it.

One important thing, also, is that PHP is quite easy to scale : just add a couple of web servers, and voila !

The problem you often meet when going from 1 to several servers is with sessions -- store those in DB or memcached (very easy), and problem solved !

As a sidenote : I would not recommend choosing a technology because there is a couple of percent difference of speed on some benchmark : there are far more important factors, like how well your team know each technology -- or, even, the algorithms you are going to use !