Support multiple $wpdb handlers

[mgibbs189]

A handful of plugins (W3 Total Cache, Query Monitor, etc.) use /wp-content/db.php for caching or query debugging. Unfortunately, only a single plugin is able to use it at once.

This patch allows multiple plugins to access WP at this stage of execution. Custom handlers can be placed into a /wp-content/db/ folder.

[johnbillion]

Could you provide an example of how this would be used? db.php files instantiate the wpdb class and assign it to $wpdb. If more than one file that did this was loaded, it wouldn't solve the problem because each one would override the previous one's $wpdb.

[mgibbs189]

Sure - I'm building AJAX caching for a plugin, and need access to WPDB as early as possible. The normal admin-ajax.php routine fully loads WP and all plugins, which in this case is unnecessary (every millisecond counts).

My use case: ​https://gist.github.com/mgibbs189/8345521

• A request is made to admin-ajax.php
• Load WPDB if it doesn't exist already
• Using WPDB, check to see if a cached version exists...
• If YES, output the cached version and EXIT
• If NO, continue loading WP

This patch will help any plugin needing to implement DB-based (ajax) caching.

[wonderboymusic]

since wp-content/db.php is a drop-in controlled by the user, why don't you just put your code in there? or why don't you add the logic to advanced-cache.php? Seems like your only need is to load early. If you are using multisite, add your logic to sunrise.php - even for single site, turn multisite on and add it to sunrise.php and exit() after conditionally. OR, access your PHP file directly from AJAX and do something like:

define( 'SHORTINIT', 1 );

require( 'wherever/wp-load.php' );

// load your special file thing
// do whatever

OR just bail on init.

[mgibbs189]

Better VCS support

[markoheijnen]

I agree with johnbillion and wonderboymusic here. The code doesn't solve the issue. It instead it will be more confusing since a normal db.php will set $wpdb and you can't control which file did set the variable.

Your use case doesn't show the need of multiple db classes. You miss use the file to execute code that doesn't involve the db handler.

[mgibbs189]

@markoheijnen - That's true, the timing could make things confusing, but I need some way to include a caching handler before WP and all the plugins fully load. In some cases, this is the difference between 20ms and 2 seconds.

@wonderboymusic's suggestion to use SHORTINIT with wp-load.php won't work because it FORCES WP to quit early. I need a way for this to happen conditionally. E.g.

• If a cache exists, then simulate SHORTINIT (quit early)
• If cache doesn't exist, then continue normal execution

[wonderboymusic]

you're describing advanced-cache.php

[mgibbs189]

@wonderboymusic - that's the problem. Only 1 plugin at a time can use advanced-cache.php, object-cache.php, or db.php. Plugins like W3 Total Cache register all of these files.

My plugin needs to work side-by-side with W3 Total Cache. W3 Total Cache isn't able to cache ajax requests. Hence the need for multiple handlers.

[mgibbs189]

Attached is another solution (wp-settings.php.patch). It checks for custom shortinit handlers before exiting.

[mgibbs189]

Closing - moving to a new ticket since this now deals less with $wpdb.

[DrewAPicture]

@mgibbs189's new ticket is here: #26806