title: Kafka Connect - Failed to flush, timed out while waiting for producer to flush outstanding messages
body: <p>I am trying to use the Kafka Connect JDBC Source Connector with following properties in BULK mode.</p>
  
  <pre><code>connector.class=io.confluent.connect.jdbc.JdbcSourceConnector
  timestamp.column.name=timestamp
  connection.password=XXXXX
  validate.non.null=false
  tasks.max=1
  producer.buffer.memory=2097152
  batch.size=1000
  producer.enable.idempotence=true
  offset.flush.timeout.ms=300000
  table.types=TABLE,VIEW
  table.whitelist=materials
  offset.flush.interval.ms=5000
  mode=bulk
  topic.prefix=mysql-
  connection.user=kafka_connect_user
  poll.interval.ms=200000
  connection.url=jdbc:mysql://&lt;DBNAME&gt;
  value.converter=org.apache.kafka.connect.json.JsonConverter
  key.converter=org.apache.kafka.connect.storage.StringConverter
  </code></pre>
  
  <p>I get the following error about committing offsets, changing various parameters seems to have little effect.</p>
  
  <pre><code>[2019-04-04 12:42:14,886] INFO WorkerSourceTask{id=SapMaterialsConnector-0} flushing 4064 outstanding messages for offset commit (org.apache.kafka.connect.runtime.WorkerSourceTask)
  [2019-04-04 12:42:19,886] ERROR WorkerSourceTask{id=SapMaterialsConnector-0} Failed to flush, timed out while waiting for producer to flush outstanding 712 messages (org.apache.kafka.connect.runtime.WorkerSourceTask)
  </code></pre>