[wp-hackers] Re: odd posts query on 404

[Casey Bisson]

I finally sat down with a completely clean and virgin install of  
WordPress 2.3.2 and traced what happens when you make a permalink  
request for a non-existent URL.

Two sets of URLs to use as examples and context:

These are valid URLs:
http://site.org/archives/101
http://site.org/page-name

These are _not_ valid URLs:
http://site.org/archivezorz/101
http://site.org/favicon.ico

Valid URLs get parsed, expected MySQL queries get executed, and the  
results are processed and returned to the browser. The problem is that  
invalid URLs that get sent through WordPress still result in a query  
like the following being executed on the database:

SELECT SQL_CALC_FOUND_ROWS  test_posts.* FROM test_posts  WHERE 1=1   
AND post_type = 'post' AND (post_status = 'pub
lish' OR post_status = 'private')  ORDER BY post_date DESC LIMIT 0, 10

That is, even after a URL is sent through WP->parse_request() and  
found to be invalid/404, WordPress marches on to WP->query_posts() and  
hits the database with a generic request for the X most recent posts.  
And because this is executed for every 404, it actually results in a  
lot of database activity.

In most cases MySQL has cached the result, and so it poses a minimal  
load on the server. And even if the cache is stale, for most sites  
it's not a particularly resource intensive query.

But, if you've got 350,000 rows in the posts table, it's incredibly  
resource intensive to order all those posts on the post_date  
(datetime) column. I've seen hundreds of them pile up and take  
_forever_ to complete after writes to the table. It's sufferable if  
write activity on the posts table is very low, but that's not  
something I want to hope for.

So here's my question:
Do we actually want to execute that query for every 404 under normal  
circumstances? If not, is this (or something like this) the stupidest  
solution?

wp-includes/classes.php:WP->query_posts()

	function query_posts() {
		global $wp_the_query;
		$this->build_query_string();

		// return if the request URI is a 404
		if( $this->did_permalink && $this->query_vars['error'] == '404' )
			return;

		$wp_the_query->query($this->query_vars);
  	}

The above works, but there's probably a better way to write it.

Thoughts?

--Casey
http://MaisonBisson.com