WP_Importer::get_imported_comments

	public function get_imported_comments( $bid ) {
		global $wpdb;

		$hashtable = array();

		$limit  = 100;
		$offset = 0;

		// Grab all comments in chunks.
		do {
			$sql     = $wpdb->prepare( "SELECT comment_ID, comment_agent FROM $wpdb->comments LIMIT %d,%d", $offset, $limit );
			$results = $wpdb->get_results( $sql );

			// Increment offset.
			$offset = ( $limit + $offset );

			if ( ! empty( $results ) ) {
				foreach ( $results as $r ) {
					// Explode comment_agent key.
					list ( $ca_bid, $source_comment_id ) = explode( '-', $r->comment_agent );
					$source_comment_id                   = intval( $source_comment_id );

					// Check if this comment came from this blog.
					if ( $bid == $ca_bid ) {
						$hashtable[ $source_comment_id ] = intval( $r->comment_ID );
					}
				}
			}
		} while ( count( $results ) == $limit );

		// Unset to save memory.
		unset( $results, $r );

		return $hashtable;
	}