Bad Gateway issue with PHP API - php

Question

Hey I made an API in PHP from my MySQL database, It is rather CPU intensive and is being called multiple times a second.
$timer = $candle_time * 60;
$DATABASE_HOST = '';
$DATABASE_USER = '';
$DATABASE_PASS = '';
$DATABASE_NAME = '';
$response = array();
$link = mysqli_connect($DATABASE_HOST, $DATABASE_USER, $DATABASE_PASS, $DATABASE_NAME);
$query = "SELECT * FROM table WHERE name LIKE 'name' ORDER BY table.datetime ASC";
$result = mysqli_query($link, $query);
while ($row = mysqli_fetch_row($result)) {
$dates .= $row[1]. ',';
$price .= $row[2]. ",";
$datetime .= $row[3]. ',';
}
$dates = explode(",",$dates);
$price = explode(",",$price);
$datetime = explode(",",$datetime);
for($i = 0; $i < count($dates); $i++){
array_push($response,array(strtotime($datetime[$i]),$dates[$i],$price[$i]));
}
$counting_segments = 0;
$grouped_prices = array();
$final_grouping = array();
$rounded = ceil($response[0][0]/$timer)*$timer;
$counted = count($response)-1;
for($i = 0; $i < count($response); $i++){
if($i == $counted){
$rounded = ceil($previous_time/$timer)*$timer;
array_push($final_grouping,array($rounded,$grouped_prices));
}
if($response[$i][0] > $rounded){
$previous_time = $response[$i][0];
array_push($final_grouping,array($rounded,$grouped_prices));
$grouped_prices = array();
$rounded = ceil($response[$i][0]/$timer)*$timer;
}
if($response[$i][0] < $rounded){
$previous_time = $response[$i][0];
array_push($grouped_prices,$response[$i][2]);
} else {
array_push($grouped_prices,$response[$i][2]);
}
}
$new_array = array();
for($i = 0; $i < count($final_grouping); $i++){
$first_array = $final_grouping[$i][0];
$second_array = $final_grouping[$i][1];
$first_price = $second_array[0];
$last_price = end($second_array);
$high_price = max($second_array);
$low_price = min($second_array);
$final_date = $first_array;
$obj = new StdClass;
$obj->time = $final_date;
$obj->open = $first_price;
$obj->high = $high_price;
$obj->low = $low_price;
$obj->close = $last_price;
array_push($new_array,$obj);
}
$json_api = json_encode($new_array);
echo $json_api
I think the reason for the 503 is the CPU power it is taking to calculate the requests. Is there a way I can have a script or something that pulls the data and saves it to a php file every second to lessen the load or is there a better way of doing this?
I did run this personally and it works perfectly, however with more people requesting from it it provides a 503 often.
Thanks.

Answer 1

The PHP code itself doesn't look like it should overload the CPU. However, there are a lot of things you can do to optimize it
How's the query performing. Execute the query directly and see if you need to add an index. This could be an index on 2 fields: name and datetime.
You're using specific columns date, price, and datetime, but you're getting all rows in the response. It's better to specify the columns you want
SELECT `date`, `price`, `datetime` FROM table WHERE name LIKE 'name' ORDER BY table.datetime ASC
You're building up comma-separated strings and then splitting them right after. That's unnecessary. Instead build-up arrays.
while ($row = mysqli_fetch_row($result)) {
$dates[] = $row[1];
$price[] = $row[2];
$datetime[] = $row[3];
}
In this case, you don't even need separate arrays, but can just build-up $response in the fetch loop.
while ($row = mysqli_fetch_row($result)) {
$response[] = array(strtotime($row[1]), $row[2], $row[3]);
}
P.S. Don't use array_push() unless you care about the inserted index. The $array[] = $value syntax is faster.
Just count once, not every iteration in the loop
$counted = count($response);
for($i = 0; $i < $counted; $i++){
if($i == $counted - 1){