An efficient alternative to paging with SQL OFFSETs

Eoin:

Paging large MySQL tables can be slow using the typical offset method. This alternative method leveraging the primary key is a more efficient solution.

Originally posted on Developer Resources:

Challenge

Running WordPress.com means having multimillion-record database tables. Tables which we often need to batch-query.

Provided we could hardly select (or update, etc) millions of records at once and expect speed, we commonly have to “page” our scripts to only handle a limited number of records at once, then move on to the next batch.

Classic, but inefficient, solution

The usual way of paging result sets in most SQL RDMS is to use the OFFSET option (or LIMIT [offset], [limit], which is the same).

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But on a performance level, this means you’re asking your DB engine to figure out where to start from all on its own, every time. Which then means it must be aware of every record before the queried offset, because they could be different between queries (deletes, etc). So the higher your offset number, the longer the overall query will take.

Alternative solution

Instead, of…

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How to debug your WordPress plugin

If you are developing a plugin on WordPress, you will need to debug your code as you go.

To enable debugging, go to your wp-config.php file.

Find the line…

define('WP_DEBUG', false);

Replace the line above with the following…

// Turns WordPress debugging on
define('WP_DEBUG', true);

// Tells WordPress to log everything to the /wp-content/debug.log file
define('WP_DEBUG_LOG', true);

// Doesn't force the PHP 'display_errors' variable to be on
define('WP_DEBUG_DISPLAY', false);

// Hides errors from being displayed on-screen
@ini_set('display_errors', 0);

Now you all warnings and errors will show up in the /wp-content/debug.log file, including WordPress warnings of deprecated functions.

You can write directly to this log from your plugin using the error_log() function.

Typically…

//output some debug string
error_log( 'this works yo' );

//output some array/object
error_log( print_r( $some_obj_or_array, 1 ) );

Kudos to this post. It has some good plugin development tips, including how to enable debugging on WordPress.

WP Plugins: How to remove a Filter

Eoin:

Do not use remove_filter(). It is possible it will break other hooks which can have unintended consequences. This post gives a really good alternative approach using static variables.

Originally posted on hakre on wordpress:

Worth to know for wordpress plugin authors: Making your plugin to safely unregister or remove a hook (filter or action) is not possible with the wordpress plugin API. Why? you might ask yourself. Even the name of the remove_filter() function suggests it and the codex documentation does say so as well.

But: It does not work, because this function does not work as intended. And beyond your own hooks, it has the potential to hinder the blog from working properly as it has the potential to remove other hooks then the specified one.

Does not is not exactly right, it does, but only sometimes. That’s specifically a bummer if you write plugins yourself, because you can not safely rely on it. For example, if running your plugin makes use of PHP 5.2 or greater it works. But it does not if it’s running on PHP 4 or PHP 5 lower…

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How to Auto-Forward Gmail Messages in Bulk

Unfortunately, Gmail will not allow you to forward old email via a filter.

gmailI found a way that you can transfer all email from one Gmail account to another, and it works but it’s a tad complicated.

If you want to simply forward old email, the solution from Digital Inspiration using Google Docs is better.
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