* All keys are stored in lowercase for case-insensitive lookup.
     */
    protected Map<String, DataStore> dataStoreMap = new LinkedHashMap<>();

    /**
     * Cached array of available data store names discovered from plugin JAR files.
     * This cache is refreshed periodically based on the lastLoadedTime.
     */
    protected volatile String[] dataStoreNames = StringUtil.EMPTY_STRINGS;

    /**

     * Adds a document to the search index by crawling the specified URL and processing the content.
     * This method handles recursive crawling with depth and access count limits, follows redirects,
     * and processes child URLs discovered during crawling.
     *
     * @param paramMap the data store parameters containing crawling configuration
     * @param dataMap the data map containing the document information including the URL
     */

    //                                                                         ===========

    /**
     * Represents an active Fess instance discovered via heartbeat.
     */
    public static class InstanceInfo {
        /** Default constructor. */
        public InstanceInfo() {
        }

        /** The unique instance ID. */