WordPress at a glance
filter is not described

split_the_query filter-hook . WP 3.4.0

Filters whether to split the query.

Splitting the query will cause it to fetch just the IDs of the found posts (and then individually fetch each post by ID), rather than fetching every complete row at once. One massive result vs. many small results.

Usage

add_filter( 'split_the_query', 'filter_function_name_8788', 10, 2 );
function filter_function_name_8788( $split_the_query, $this ){
	// filter...

	return $split_the_query;
}
$split_the_query(true/false)
Whether or not to split the query.
$this(WP_Query)
The WP_Query instance.

Where the hook is called

WP_Query::get_posts()
wp-includes/class-wp-query.php 2804
$split_the_query = apply_filters( 'split_the_query', $split_the_query, $this );

Where the hook is used (in WP core)

Does not used.