Multisite

Event	Behaviour
Network activation	Activation runs on every site of the current network.
Single-site activation	Runs on that site only.
New site created while network-active	The site is set up automatically (`wp_initialize_site`).
Network deactivation	Deactivation runs on every site.
Uninstall	Data is removed from every site of the network.
Site deleted	Its custom tables are dropped (`wpmu_drop_tables`). Its options go with its options table.
Upgrade	Each site upgrades itself on its first request after the update, since the version is stored per site.

Large networks

Looping over thousands of sites in one request can time out. Filter the site list to process a subset, then handle the rest in the background, for example with Action Scheduler:

add_filter( 'acme_network_site_ids', function ( array $ids ) {
	if ( count( $ids ) <= 100 ) {
		return $ids;
	}
	foreach ( array_slice( $ids, 100 ) as $id ) {
		as_enqueue_async_action( 'acme_activate_site', [ $id ] );
	}
	return array_slice( $ids, 0, 100 );
} );

add_action( 'acme_activate_site', function ( int $id ) {
	switch_to_blog( $id );
	Bignall\WPFoundation\Plugin::instance( 'acme/acme.php' )->lifecycle()->activateSite();
	restore_current_blog();
} );

Per-site upgrades are already lazy, so they don't need this.

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Multisite

#Large networks

Large networks