Re:PHP doesn't scale? (Score 3, Insightful)

More than anything I was curious about server side Java in particular, which you claim is more scalable because it shares memory. I'm interested in hearing some more details about this - why you think it's so and any references to back it up.

Java is not more scalable than PHP by its own because it shares memory. Java enables/simplifies the design of scalable applications, which is not exactely the same. If there is nothing to share, then the execution model doesn't matter. If you can capilize on stuff created once for all, or at least reusable several times, then being able to share memory has a big impact.

"Java-based SEDA Web server outperforms Apache and Flash (sld12)" because of a design aimed at limiting object reinstantiations and context switching. These two pains obviously occur when you do the same things on many concurrent threads: you'd better do it once and share the result.

There is really nothing special with Java and multi-threading about that. The same is true for multi-process Apache C modules programmed to use shared memory.
In fact all four components of the LAMP architecture internally make extensive usage of shared memory (for i in linux apache mysql php; do google "shared memory" $i ; done) simply because cpu cycles and memory allocations are expensive and high performance objectives imply not to waste them. If PHP had a higher level API than its existing one for managing shared memory, web programmers would be able to easily prolong the benefit of using shared memory to the application itself.

I shouldn't end my post with a flamebait but I believe that if a web developer suffers from Java's drawbacks (bytecode/JVM, performance cost of native UTF-16 strings, garbage collection, ...), he's 99% likely to under-use its strengths (great thread API, servlet model, great librairies, ...). Well used, they enable really performant designs. I've seen so many times applications refactored from C to Java performing several times faster, just because it was easy to do things smarter in Java, while very risky in C (Never had a SIGSEGV in a large multi-threaded C application ? Happy debugging and next time you'll keep it stupid!).