Question

I have read for years about ways to conserve memory when writing php scripts. But what type of scripts should I really concern myself with. What codes/scripts/call eat the most memory?

Edit

This is a question, please do not answer it with a question

Edit

What about this. Does something like this eat memory? It needs to be done but should it be freed some how?

$manufacture = htmlspecialchars($_REQUEST["manufacture"]);
$manufacture = preg_replace("/[^0-9]/","", $manufacture);



$SQL = "SELECT * FROM STORE_MANUFACTURERS WHERE manufacturers_id = '$manufacture'";
$result = mysql_query( $SQL );
while( $row = mysql_fetch_array( $result ) ) {
$manufacturers_name = $row['manufacturers_name'];
}

Answer 1

There are so many things to think when you go for a 100% perfect out look regarding memory leak. What I do is to follow the coding standards and patterns . and if I get into memory leak trouble even after that I should figure that out with profiling Tools like XDebug or Kcachegrind.

Things Like Exception safety should be well maintained

You can use tools like memory_get_peak_usage() , memory_get_usage() to spot the culprit. You may check out this post regarding Memory Manager.

Scripting Languages like PHP uses automatic garbage collection e.g. you don’t have to dealloc by yourself. the garbage collector does it for you (using reference counting). but if you want to do it by yourself you may use unset(). but some scenarios has been reported when even unset doesn’t do it for you. Some Bugs have been reported regarding this too. bug#33945 bug#33487

reference counting will run into problem when both a:A and b:B have a circular reference so you need the one instance to take the ownership and destruct the referred object to break the circle to face this issue.

There are some issues with strtotime() memory leak bug#47285

The code you have posted in your edit shouldn’t have any concern of having memory leak. I’ll quote @GolezTrol in comments

All memory allocated by the script is freed as soon as it terminates,
which is at the end of each request. You shouldn’t really have any
concerns unless you are building special scripts or have a website
with a very high load. If you have to have this question like this,
you probably have neither, so don’t worry about it.