WordPress at a glance
function is not described

wpmu_log_new_registrations() WP 3.0.0

Logs the user email, IP, and registration date of a new site.

  • Global. wpdb. $wpdb WordPress database abstraction object.
  • Since 5.1.0 Parameters now support input from the 'wp_initialize_site' action.

No Hooks.

Return

Nothing (null).

Usage

wpmu_log_new_registrations( $blog_id, $user_id );
$blog_id(WP_Site/int) (required)
The new site's object or ID.
$user_id(int/array) (required)
User ID, or array of arguments including 'user_id'.

Code of wpmu log new registrations: wp-includes/ms-functions.php VER 5.1.1

<?php
function wpmu_log_new_registrations( $blog_id, $user_id ) {
	global $wpdb;

	if ( is_object( $blog_id ) ) {
		$blog_id = $blog_id->blog_id;
	}

	if ( is_array( $user_id ) ) {
		$user_id = ! empty( $user_id['user_id'] ) ? $user_id['user_id'] : 0;
	}

	$user = get_userdata( (int) $user_id );
	if ( $user ) {
		$wpdb->insert(
			$wpdb->registration_log,
			array(
				'email'           => $user->user_email,
				'IP'              => preg_replace( '/[^0-9., ]/', '', wp_unslash( $_SERVER['REMOTE_ADDR'] ) ),
				'blog_id'         => $blog_id,
				'date_registered' => current_time( 'mysql' ),
			)
		);
	}
}