public BufferingNoOpRequestIndexer<Request> getFailureRequestIndexer() {
        return failureRequestIndexer;
    }
Get pending requests for handle in subClass

@return The numPendingRequests
inlong-sort/sort-flink/sort-flink-v1.13/sort-connectors/elasticsearch-base/src/main/java/org/apache/inlong/sort/elasticsearch/ElasticsearchSinkBase.java