public void setBulkFlushBackoffType(FlushBackoffType flushBackoffType) {
            this.bulkRequestsConfig.put(
                    CONFIG_KEY_BULK_FLUSH_BACKOFF_TYPE,
                    Preconditions.checkNotNull(flushBackoffType).toString());
        }
Sets the type of back of to use when flushing bulk requests.

@param flushBackoffType the backoff type to use.
inlong-sort/sort-flink/sort-flink-v1.13/sort-connectors/elasticsearch-6/src/main/java/org/apache/inlong/sort/elasticsearch6/ElasticsearchSink.java