WordPress being slow, a DNS problem

A friend of mine runs a WordPress site and recently moved to a different provider. The transition went smoothly and the site ran fine for three weeks. One day he made a post like he normally does and the site become very slow. He deleted the post but with no result. His site was still extremely slow, I mean it took almost a minute to load the index page. Installation of a caching plugin, deactivating all plugins, selecting the default theme did not help at all.

Using Firefox with Firebug I saw that the problem seem to be with php files, both the index.php and wpsf-js.php, a part of WP-Spamfree, took 20 seconds to load.
The thing is though that he also runs a phpBB forum and there were no problems with the forum, also uploading a new php file, to show phpinfo(), run perfectly. It had to do with WordPress.

After some searching on the net it turns out to be a problem with the provider. The server on which the site is running, unable to resolve it’s own address.

Why is this a problem?

WordPress uses a program wp-cron.php which is called when a certain amount of time has passed.
Every time your blog is accessed by a user WordPress checks if the time is there to call wp-cron.php by comparing the time wp-cron.php last ran and the current time and when it determines it needs to run wp-cron.php it does so.
The way wp-cron.php is called is by the PHP fsockopen and doing a HTTP call. One of the parameters is your site’s URL. The fsockopen function needs to resolve that name to an IP address, that’s just the basics of the internet.
I guess you see the problem now, the function runs on the server and tries to resolve it’s own name. Which in this case doesn’t work.

Determine if this is the case

Before you go yelling at your provider they need to fix this, you better check if this is really the case.

If your provider gives you cPanel you can quickly check it by going to the Network Tools and try to resolve your website. If it comes back with an error, you can yell at your provider.

If you don’t have cPanel or you just don’t have the ability to do a DNS check you can use the method:
Create a file called cron-test.php and insert the following code.

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<?php
$argyle = fsockopen( 'example.com', 80, $errno, $errstr, 0.01 );
if ( $argyle ) {
fputs( $argyle, "GET /wp-cron.php HTTP/1.0\r\n"
. "Host: example.com\r\n\r\n" );
echo "Success sending the GET.\n";
} else {
echo "Error: $errstr ($errno)\n";
}
?>

Replace example.com on lines 2 and 5 with your site’s address and upload this in the root of your blog. If your blog resides in a directory upload the file there and change the GET /wp-cron.php to GET /your_directory/wp-cron.php

Now point your browser to http://example.com/cron-test.php and see if it succeeds or returns an error.
If the error has failure in name resolution in it’s message you have the DNS problem.

Solution.

The best way to solve this problem is to contact your provider, tell them the server can’t resolve its own IP address. If they know what they are doing they should be able to fix that. If they can’t or they just plainly tell you they won’t there is another solution.
You’ll have to add a line in a core file of WordPress. This comes with a problem though, when you upgrade WordPress you’ll have to change that file again.But I guess it’s better as having a slow website.

The hack

If you want to go ahead with hacking the core file, lets make sure the hack actually works.
We’ll apply the hack first to the above file.

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<?php
$host_ip = $_SERVER[SERVER_ADDR];
$argyle = fsockopen( $host_ip, 80, $errno, $errstr, 0.01 );
if ( $argyle ) {
fputs( $argyle, "GET /wp-cron.php HTTP/1.0\r\n"
. "Host: example.com\r\n\r\n" );
echo "Success sending the GET.\n";
} else {
echo "Error: $errstr ($errno)\n";
}
?>

Point your browser at the file again and it should return Success… if not let me know what error message you get and I’m sorry for now I don’t know how to solve it.

If it does work lets go ahead and starting applying the hack to the core file wp-includes/cron.php.
Open it in you favorite editor and search for:

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function spawn_cron() {
	$crons = _get_cron_array();
 
	if ( !is_array($crons) )
		return;
 
	$keys = array_keys( $crons );
	if ( array_shift( $keys ) > time() )
		return;
 
	$cron_url = get_option( 'siteurl' ) . '/wp-cron.php';
	$parts = parse_url( $cron_url );
 
	if ($parts['scheme'] == 'https') {

We’ll add a line after line 12 so the part looks like this

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function spawn_cron() {
	$crons = _get_cron_array();
 
 
	if ( !is_array($crons) )
		return;
 
	$keys = array_keys( $crons );
	if ( array_shift( $keys ) > time() )
		return;
 
	$cron_url = get_option( 'siteurl' ) . '/wp-cron.php';
	$parts = parse_url( $cron_url );
	$parts['host'] = $_SERVER['SERVER_ADDR'];
 
	if ($parts['scheme'] == 'https') {

And that’s it, save the file and your site should be running smoothly again.
Update on Dec 6, 2008, I forgot to put SERVER_ADDR in quotes, sorry for that

This entry was posted on Wednesday, December 3rd, 2008 at 9:04 pm and is filed under WordPress. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.