Does the body of my function get read every time? - php

Question

I'm building a WordPress theme and trying to determine what is causing it to run so slowly. Myfunctions.php is about 500 lines and has functions that interact with the database such as
add_action( 'wp_ajax_nopriv_get_N_more', 'get_N_more' );
add_action( 'wp_ajax_get_N_more', 'get_N_more' );
$N = 9;
function get_N_more ( )
{
global $wpdb, $N;
$thisTable = ($_POST['workType'] === 'projs') ? 'wp_nas_projs' : 'wp_nas_cases';
$q = $wpdb->prepare( "SELECT id,compname,descsmall,sumsmall,imageurl FROM $thisTable ORDER BY postdate DESC LIMIT %d, %d", intval($_POST['numItemsLoaded']), $N);
$nextNRows = $wpdb->get_results($q);
removeEscapes($nextNRows);
$stillSomeLeft = ($_POST['numItemsLoaded'] + $N) < count($wpdb->get_results($wpdb->prepare("SELECT * FROM $thisTable")));
// ^ would like more efficient way of doing above
die(json_encode(array('stillSomeLeft' => $stillSomeLeft, 'workItems' => $nextNRows)));
}
Such functions are not called every time the script is read, however I'm wondering if having them there in the first place could be creating performance slowdowns if PHP has read through them every time.

Answer 1

The short answer is maybe.
If you are calling do_action(...) several times on those actions you have added, then it could be the case that multiple ajax requests are being made and either are timing out or being cancelled as new requests are being issued.
The main reason that you could have a very slow running page is that you are working directly with the database. If these are custom tables then there is a good probability that your indexes are not set correctly and the query is taking forever to return or is timing out.
You should consider using get_posts or the WP_Query for posts or pages as you can then use the native wordpress functions to extract data. If you have made a custom post type then store your data in the post_meta and use wordpress core functions versus a secondary table.
In general if your queries will be returning the same information on nearly every page load you might want to consider storing them to cache so you are not recalculating every page load.
What does all of this mean?
Check your database table indexes. Run the query as it is built by your code in something like mysql workbench.
Open up your browser console or firebug and look at the ajax requests being made when you load your pages.
Check all the places you are calling do_action and adjust accordingly.
When debugging print things to a file or to the screen. This will help tremendously.

Answer 2

PHP must only be reading your functions once during the request, therefore not causing a slowdown.
Look at the definition of your function:
function get_N_more ( )
{
}
It's not guarded in a check to function_exists(). This means that, if this file were parsed anywhere more than once, execution would fail and report an error that your get_N_more function is already declared in this scope.
The complexity and runtime efficiency of the code is never taken into account during parsing of the script, and 500 lines is a relatively trivial amount of code.
tl;dr: This isn't the cause of your slowdown.