WordPress: Cache patterns for complex queries

## cache-patterns-in-wordpress.php
<?php
/**
 * Retrieve a WP_Query object
 */
function my_complex_query( $refresh = false ) {

	$last_changed = wp_cache_get_last_changed( 'my_group_my_post_type' );

	$cache_key = 'my_result'.md5( $param1 . $param2 ).$last_changed;

	if ( $refresh || false === ( $results = wp_cache_get( $cache_key ) ) ) {

		$query_args = array(); // define my query args using $param1 and $param2

		$results = new WP_Query( $query_args );

		wp_cache_set( $cache_key, $results, 'my_group', HOUR_IN_SECONDS );

	}
	return $results;
}

/**
 * Hook on save_post to burn a new 'last_changed' timestamp
 */
function my_theme_flush_cache( $post_id ) {
	wp_cache_set( 'last_changed', microtime(), 'my_group_'.get_post_type( $post_id )  );
}
add_action( 'save_post', 'my_theme_flush_cache' );