WordPress at a glance
filter is not described

do_mu_upgrade filter-hook . WP 3.0.0

Filters whether to attempt to perform the multisite DB upgrade routine.

In single site, the user would be redirected to wp-admin/upgrade.php. In multisite, the DB upgrade routine is automatically fired, but only when this filter returns true.

If the network is 50 sites or less, it will run every time. Otherwise, it will throttle itself to reduce load.

Usage

add_filter( 'do_mu_upgrade', 'filter_function_name_6270' );
function filter_function_name_6270( $do_mu_upgrade ){
	// filter...

	return $do_mu_upgrade;
}
$do_mu_upgrade(true/false)
Whether to perform the Multisite upgrade routine.
Default: true

Where the hook is called

In file: /wp-admin/admin.php
do_mu_upgrade
wp-admin/admin.php 64
} elseif ( apply_filters( 'do_mu_upgrade', true ) ) {

Where the hook is used (in WP core)

Does not used.