Cthree and Krazik,

Have you guys tried PHP Accelerator (phpa - http://www.php-accelerator.co.uk/) on the servers? I read recently that you have a bank of three servers. I had a similar setup at an old job and a developer put the free PHP accelerator on our three boxes (round robin under a load balancer) and we could handle 12x the transaction volume instantly with no code changes -- we were fulfilling 600,000 ecommerce transactions a day with three cheapie boxes. I'm not a programmer so I don't know what the installation entails but I heard that it was easy, quick, and painless. You guys may want to give it a shot if you haven't yet.

 

Every time a PHP script is accessed, the PHP engine must open the script file and read, parse, and compile the file contents into a compiled form. Only then can the compiled code be executed. With scripts often including other scripts, this work can become a significant part of the overall time to deliver a page. It can also impact I/O performance, and require much dynamic memory allocation that in itself can be time consuming.

The reality, however, is that most PHP scripts never change from one access to the next; indeed they may never change for weeks, months, or even years. The Accelerator works to eliminate the penalty of processing scripts that never change, and by caching the compiled scripts in shared memory, delivers significant performance gains as a result. Note that this is very different to caching script output. PHPA doesn't do this, scripts remain fully dynamic, and if they do change then PHPA caches a new version - they just run faster!

So by caching, the Accelerator eliminates:


reading of source code
parsing of source code
compiled code generation
many memory allocation and copying operations
disk related operations
Once script execution has completed, compiled versions of any new or modified scripts are immediately cached on disk for later reuse. This guarantees good acceleration, but scripts are then cached in shared memory, and offering the maximum performance gains.
The Accelerator has one other performance enhancing feature - a built-in code optimiser. Although in it's early stages, the optimiser reduces the size of compiled code and improves the code by removing unnecessary operations.

So in summary, by aggressively removing operations causing performance overhead, the Accelerator is able to deliver performance rivalling the very best alternatives, and for free!

There are also a few performance tests and testimonials that illustrate the potential impact of the Accelerator.

 

we've been running phpa for a LONG time.

It works great. Cut our load at the time to about 1/5th the previous levels.

Thank you for the sugestion, but the problem is the sites code itself no ammount of caching can help that

 

speaking of caching not only do we use phpa, but we also use squid running in httpd accelerator mode infront of apache on all 3 s2ki web servers. So apache sees no static image requests also reducing the load even more.

Even with all that, we still run a LA of about 4-8 on all 3 webservers (single cpu P4s ~2.4G)

 

D'oh! That's the worst kind of slowdown. It's always easier to just throw money at things

Good luck and thanks for the great site!

 

Interesting. In our case, our DB server is the one that is thrashed and the webservers are cruising along at almost no load. Then again, our DB server does all of the work (sorting, filtering, etc.). The webservers just spit out HTML.