@Override
		public void beforeBulk(long executionId, BulkRequest request) {

			// verify client connection.
			if ((System.currentTimeMillis() - lastVerifyTime) >= verifyInterval) {
				try {
					long currentTimeMillis = System.currentTimeMillis();
					callBridge.verifyClientConnection(client);
					lastVerifyTime = currentTimeMillis;
				} catch (IOException e) {
					LOG.error("Verify and Refresh ClientConnection failed. Reason: {}", e.getMessage());
					failureThrowable.compareAndSet(null, e);
				}
			}

		}
The interval time which check client whether available.
elasticsearch5-xh/elasticsearch5-xh-sink/src/main/java/org/apache/flink/streaming/connectors/elasticsearch/ElasticsearchSinkBase.java