CODEWITHSUNDEEP
phplaravel
fico7489
fico7489

Reputation: 8560

Does file_get_contents use cache? If it does how do I prevent?

With this code :

for($i = 1; $i <= $times; $i++){
    $milliseconds = round(microtime(true) * 1000);
    $res = file_get_contents($url);
    $milliseconds2 = round(microtime(true) * 1000);

    $milisecondsCount = $milliseconds2 - $milliseconds;
    echo 'miliseconds=' . $milisecondsCount . ' ms' . "\n";
}

I get this output :

miliseconds=1048 ms
miliseconds=169 ms
miliseconds=229 ms
miliseconds=209 ms
....

But with sleep:

for($i = 1; $i <= $times; $i++){
    $milliseconds = round(microtime(true) * 1000);
    $res = file_get_contents($url);
    $milliseconds2 = round(microtime(true) * 1000);

    $milisecondsCount = $milliseconds2 - $milliseconds;
    echo 'miliseconds=' . $milisecondsCount . ' ms' . "\n";
    sleep(2);
}

This :

miliseconds=1172 ms
miliseconds=1157 ms
miliseconds=1638 ms
....

So what is happening here ?

Upvotes: 1

Views: 1471

Answers (2)

Ajesh Nair
Ajesh Nair

Reputation: 26

Concatenate a random query string with url. For eg: $url = 'http://example.com/file.html?r=' . rand(0, 9999);

Upvotes: 1

Martin
Martin

Reputation: 22760

My questions:

1) Why don't you test this yourself by using clearstatcache and checking the time signatures with and without using it?

2) Your method of testing is terrible, as a first fix - have you tried swapping so that the "sleep" reading function plays first rather than second?

3) How many iterations of your test have you done?
If it's less than 10,000 then I suggest you repeat your tests to be sure to identify firstly the average delay (or lack thereof) and then what makes you think that this is caused specifically by caching?

4) What are the specs. of your machine, your RAM and free and available memory upon each iteration?

5) Is your server live? Are you able to remove outside services as possible causes of time disparity? (such as anti-virus, background processes loading, server traffic, etc. etc.)?

My Answer:

However, operating system level caches may cache recently used files to make for quicker access, but I wouldn't count on those being available.

Calling a file reference multiple times will only read the file from disk a single time, subsequent calls will read the value from the static variable within the function. Note that you shouldn't count on this approach for large files or ones used only once per page, since the memory used by the static variable will persist until the end of the request. Keeping the contents of files unnecessarily in static variables is a good way to make your script a memory hog.

Quoted from This answer.

  • For remote (non local filesystem) files, there are so many possible causes of variable delays that really file_get_contents caching is a long way down the list of options.

  • As you claim to be connecting using a localhost/ reference structure, I would hazard (but not certain) that your server will be using various firewall and checking techniques to check the incoming request which will add a large variable to the time taken.

Upvotes: 1

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