<p>Hi i need to generate 9 digit unique account numbers. Here is my pseudocode:</p>

<pre><code>function generateAccNo()

    generate an account number between 100,000,000 and 999,999,999

    if the account number already exists in the DB 
        call generateAccNo()    /* recursive call */
    else
        return new accout number
    end if

end function
</code></pre>

<p>The function seems to be working well, however I am a bit worried about the recursive call. </p>

<p>Will this cause any memory leaks (PHP 5 under apache)?</p>

<p>Is this an acceptable way to tackle this problem?</p>

<p>Thanks for your input.</p>

You realize this could very well cause a stack overflow, right? As the number of customesr increases, the probability of not finding a an acceptable account number increases.
Also, why can't you just do sequential account numbers and just increase by one every time? With this approach, you'd just have to read the max id currently in the database and just increment it.
Sorry to be so blunt, but your solution is a terrible way to tackle the problem. It'll use tons of memory (as the stack possibly grows infinitely) and it will makes tons of expensive calls to the database.
You should really consider some other approach:
I strongly recommend just incrementing the customer number every time you create a customer. In fact, if you set up your db properly (with auto increment on the id column), you won't even have to set the id. The id will be set for you whenever you insert a new customer.