When should I unset in PHP to improve performance - php

Question

I am using the following code:
for ($x = 0; $x < count($response[0]); $x++) { //approx count 50-60
$t = $response[0][$x];
$query = "INSERT INTO tableX (time,title) VALUES ('$date','$t')";
if ($query_run = mysqli_query($mysql_connect, $query)) {
//Call some functions if the insertion happens
}
}
mysqli_close($mysql_connect);
Title in the table is a pimary key. I am going to call some functions only when the insertion is successful i.e., no existing title is provided. The title and date are derived from a csv file.
How can I improve the performance of this code? When should I use unset to save CPU memory cycles?

Answer 1

unset will not improve performance by any meaningful metric here.
What will improve performance is updating more than one row per query.
Let's take your code as an example. This is just an example of how it could be. If you need to run other functions after the insert, then you might want to update for example 10 or 100 rows at a time instead of ALL rows.
$query = "INSERT INTO tableX (time,title) VALUES ";
$valueQuery = array();
for ($x = 0; $x < count($response[0]); $x++) { //approx count 50-60
$t = $response[0][$x];
$valueQuery[] = "('$date','$t')";
}
$query .= implode(", ",$valueQuery);
if ($query_run = mysqli_query($mysql_connect, $query)) {
//Call some functions if the insertion happens
}

Answer 2

This question is entirely based on the wrong premises.
First of all, nowhere using unset will save you a CPU cycle,but will rather cousume them.
Besides, there is not much place to put unset anyway.
Finally, there are no real issues with performance with this code. If you are experiencing any, you should meausere them, detect a real bottleneck, and then fix it, instead of poking around barking at random trees.
What should be your actual concern, instead of fictional performance issues, is that your code wide open to sql injections and syntax errors of all sorts.

Answer 3

You could improve the shown code by using prepared statements for your insert (1). As it is, in every iteration you first have to define the $query and then execute. In each execution the database would also have to first parse your statement.
By preparing the statement before entering the loop you only define it once and can just execute it with the different values. Also the statement would only be parsed when it gets prepared, it doesn't get parsed on each execute.
Here is a small artice on how the garbage-collector in php works: http://www.hackingwithphp.com/18/1/10, found in this question: Is there garbage collection in PHP?
PHP performs garbage collection at three primary junctures:
When you tell it to
When you leave a function
When the script ends
So maybe you should check how much of your programm you can encapsulate into functions, though there is not much to see in your snippet.
(1)
I suggest the prepared statements to improve efficiency. It is imo best practice to reduce workload - the unneccessary parsing of the query.
So I have no estimation on the actual performance improvement, though as this case is talking about 50 to 60 iterations it would be minimal if even noticable.