Source

File: wp-includes/class-wp-embed.php

public function find_oembed_post_id( $cache_key ) {
		$cache_group    = 'oembed_cache_post';
		$oembed_post_id = wp_cache_get( $cache_key, $cache_group );

		if ( $oembed_post_id && 'oembed_cache' === get_post_type( $oembed_post_id ) ) {
			return $oembed_post_id;
		}

		$oembed_post_query = new WP_Query(
			array(
				'post_type'              => 'oembed_cache',
				'post_status'            => 'publish',
				'name'                   => $cache_key,
				'posts_per_page'         => 1,
				'no_found_rows'          => true,
				'cache_results'          => true,
				'update_post_meta_cache' => false,
				'update_post_term_cache' => false,
				'lazy_load_term_meta'    => false,
			)
		);

		if ( ! empty( $oembed_post_query->posts ) ) {
			// Note: 'fields' => 'ids' is not being used in order to cache the post object as it will be needed.
			$oembed_post_id = $oembed_post_query->posts[0]->ID;
			wp_cache_set( $cache_key, $oembed_post_id, $cache_group );

			return $oembed_post_id;
		}

		return null;
	}