PHP Memory differing server to server - php

Question

I have a hefty PHP script.
So much so that I have had to do
ini_set('memory_limit', '3000M');
set_time_limit (0);
It runs fine on one server, but on another I get: Out of memory (allocated 1653342208) (tried to allocate 71 bytes) in /home/writeabo/public_html/propturk/feedgenerator/simple_html_dom.php on line 848
Both are on the same package from the same host, but different servers.
Above Problem solved new problem below for bounty
Update: The script is so big because it rawls a site and parsers data from 252 pages, including over 60,000 images, which it makes two copies of. I have since broken it down into parts.
I have another problem now though. when I am writing the image from outside site to server like this:
try {
$imgcont = file_get_contents($va); // $va is an img src from an array of thousands of srcs
$h = fopen($writeTo,'w');
fwrite($h,$imgcont);
fclose($h);
} catch(Exception $e) {
$error .= (!isset($error)) ? "error with <img src='" . $va . "' />" : "<br/>And <img src='" . $va . "' />";
}
All of a sudden it goes to a 500 internal server error page and I have to do it again, at which point it works, because files are only copied it they don't already exist. Is there anyway I can receive the 500 response code and send it back it to the url to make it go again? As this is to all be an automated process?

Answer 1

If this is memory related, I would personally use copy() rather than file_get_contents(). It supports the file wrappers the same way, and I don't see any advantage in loading the whole file in memory just to write it back on the filesystem.
Otherwise, your error_log might give you more information as of why the 500 happens.

Answer 2

There are three parties involved here:
Remote - The server(s) that contain the images you're after
Server - The computer that is running your php script
Client - Your home computer if you are running the script from a web browser, or the same computer as the server if you are running it from Cron.
Is the 500 error you are seeing being generated by 'Remote' and seen by 'Server' (i.e. the images are temporarily unavailable);
Or is it being generated by 'Server' and seen by 'Client' (i.e. there is a problem with your script).
If it is being generated by 'Remote', then see Ali's answer for how to retry.
If it is being generated by your script on 'Server', then you need to identify exactly what the error is - the php error logs should give you more information. I can think of two likely causes:
Reaching PHP's time limit. PHP will only spend a certain amount of time working before returning a 500 error. You can set this to a higher value, or regularly re-set the timer with a call to set_time_limit(), but that won't work if your server is configured in safe mode.
Reaching PHP's memory limit. You seem to have encoutered this already, but worth making sure you're script still isn't eating lots of memory. Consider outputing debug data (possibly only if you set $config['debug_mode'] = true or something). I'd suggest:
try {
echo 'Getting '.$va.'...';
$imgcont = file_get_contents($va); // $va is an img src from an array of thousands of srcs
$h = fopen($writeTo,'w');
fwrite($h,$imgcont);
fclose($h);
echo 'saved. Memory usage: '.(memory_get_usage() / (1024 * 1024)).' <br />';
unset($imgcont);
} catch(Exception $e) {
$error .= (!isset($error)) ? "error with <img src='" . $va . "' />" : "<br/>And <img src='" . $va . "' />";
}
I've also added a line to remove the image from memory, incase PHP isn't doing this correctly itself (in theory that line shouldn't be necessary).
You can avoid both problems by making your script process fewer images at a time and calling it regularly - either using Cron on the server (the ideal solution, although not all shared webhosts allow this), or some software on your desktop computer. If you do this, make sure you consider what will happen if there are two copies of the script running at the same time - will they both fetch the same image at the same time?

Answer 3

So it sounds like you're running this process via a web browser. I'm guessing that you may be getting the 500 error from Apache timing out somehow after a certain period of time or the process dies or something funky. I would suggest you do one of the following:
A) Move the image downloading to a background process, you can run the crawl script in the browser which will write the urls of the images to be downloaded to the db or something and another script will fire up via cron and fetch all the images. You could also have this script work in batches of 100 or so at a time to keep memory consumption down
B) Call the script directly from the command line (this is really the preferred method for something like this anyway, and you should still probably separate the image fetching to another script)
C) If the command line is not an option for some reason, have your browser loaded script touch a file, and have a cron that runs every minute and looks for the file to exist. Then it fires up your script, you can have the output written to a file for you to check later or send an email when it's completed

Answer 4

Is there anyway I can receive the 500 response code and send it back it to the url to make it go again? As this is to all be an automated process?
Here's the simple version of how I would do it:
function getImage($va, $writeTo, $retries = 3)
{
while ($retries > 0) {
if ($imgcont = file_get_contents($va)) {
file_put_contents($writeTo, $imgcont);
return true;
}
$retries--;
}
return false;
}
This doesn't create the file unless we successfully get our image file, and will retry three times by default. You will of course need to add any require exception handling, error checking, etc.

Answer 5

I would definitely stop using file_get_contents() and write the files in chunks, like this:
$read = fopen($url, 'rb');
$write = fope($local, 'wb');
$chunk = 8096;
while (!feof($read)) {
fwrite($write, fread($read, $chunk));
}
fclose($fp);
This will be nicer to your server, and should hopefully solve your 500 problems. As for "catching" a 500 error, this is simply not possible. It is an irretrievable error thrown by your script and written to the client by the web server.

Answer 6

I'm with Swish, this is not really the kind of task that PHP is intended for - you'de be much better using some sort of server side scripting.
Is there anyway I can receive the 500 response code and send it back it to the url to make it go again?
Have you considered using another library? Fetching files from an external server seems to me more like a job for curl or ftp than file_get_content &etc. If the error is external, and you're using curl, you can detect the 500 return code and handle it appropriately without crashing. If not, then maybe you should split your program into two files - one of which fetches a single file/image, and the other that uses curl to repeatedly call the first one. Unless the 500 error means that all php execution crashes, you would be able to detect the failure and handle it.
Something like this pseudocode:
file1.php:
foreach(list_of_files as filename){
do {
x = call_curl('file2.php', filename);
}
while(x == 500);
}
file2.php:
filename=$_GET['filename'];
results = use_curl_to_get_page(filename);
echo results;

Answer 7

Thanks for all your input. I had seperated everything by the time I wrote this question, so the crawler, fired the image grabber, etc.
I took on board the solution to split the number of images, and that also helped.
I also added a try, catch round the file read.
This was only being called from the browser during testing, but now that it is all up and running it is going to be a cron job.
Thanks Swish and Benubird for your particularly detailed and educational answers. Unfortunately I had no cooperation with the developers on the backend where the images are coming from (long and complicated story).
Anyway, all good now so thanks. (Swish how do you call a script from the command line, my knowledge of this field is severely lacking?)