On his blog today, Alex Netkachov has posted a suggestion of how to combat a common issue facing PHP scripts - their memory usage.

PHP has a build-in garbage collector so you do not need to track the links on the objects, allocate memory for objects and delete them when they are not longer necessary. Things seem so perfect that developers do not even know that their scripts allocate a lot of memory until their server stops processing requests because of the out of memory error.

His example is the processing of a parent/child relationship tree. If not managed correctly, the variables being used could get out of hand quite quickly. Alex recommends the use of a "destructor" at the end of each iteration to help destroy variables and values no longer needed.

In a new post, Derick Rethans talks about circular references (a reference of a memory structure back to itself) and how they relate to PHP.

Circular-references has been a long outstanding issue with PHP. They are caused by the fact that PHP uses a reference counted memory allocation mechanism for its internal variables. This causes problems for longer running scripts (such as an Application Server or the eZ Components test-suite) as the memory is not freed until the end of the request. But not everybody is aware on what exactly the problem is, so here is a small introduction to circular references in PHP.

He starts by explaining what's so bad about circular references - issues not only with referencing the variable but also with freeing up the resources associated with it. He does suggest some solutions to the issue including garbage collection and cyclic tracing.