static long isolateTimeFromIndexName(String indexName) {
        return Long.parseLong(indexName.substring(indexName.lastIndexOf(Const.LINE) + 1));
    }
@return the index represented time, which is included in the index name.
oap-server/server-storage-plugin/storage-elasticsearch-plugin/src/main/java/org/apache/skywalking/oap/server/storage/plugin/elasticsearch/base/TimeSeriesUtils.java