title: Connection timeout error in Cassandra even after specifying timeout range to be large enough(50s)
body: <p>I have written a Python script that reads rows from CSV file and then inserts it into Cassandra. It runs all alright but after certain insertions, it receives a timeout error.</p>
  
  <pre><code># lets do some batch insert
      def insert_data(self):
          start_time = datetime.utcnow()
          destination = "/Users/aviralsrivastava/dev/learning_dask/10M_rows.csv"
          chunksize = 1000
          chunks = pd.read_csv(destination, chunksize=chunksize)
          chunk_counter = 0
          for df in chunks:
              df = df.to_dict(orient='records')
              chunk_counter += 1
              batch = BatchStatement()
              for row in df:
                  key = str(row["0"])
                  row = json.dumps(row, default=str)
                  insert_sql = self.session.prepare(
                      (
                          "INSERT INTO  {} ({}, {}, {}) VALUES (?,?,?)"
                      ).format(
                          self.table_name, "id", "version", "row"
                      )
                  )
                  batch.add(insert_sql, (key, "version_1", row))
              self.session.execute(batch)
              self.log.info("One chunk's Batch Insert Completed")
              print(
                  str(chunk_counter*chunksize) + " : " +
                  str(datetime.utcnow() - start_time)
              )
              del batch
          print("Complete task's duration is: {}".format(
              datetime.utcnow() - start_time))
  </code></pre>
  
  <p>The code for establishing a connection is as follows:</p>
  
  <pre><code>def createsession(self):
          self.cluster = Cluster(['localhost'], connect_timeout = 50)
          self.session = self.cluster.connect(self.keyspace)
  </code></pre>
  
  <p>And the error is:</p>
  
  <pre><code>2019-01-16 15:58:49,013 [ERROR] cassandra.cluster: Error preparing query:
  Traceback (most recent call last):
    File "cassandra/cluster.py", line 2402, in cassandra.cluster.Session.prepare
    File "cassandra/cluster.py", line 4062, in cassandra.cluster.ResponseFuture.result
  cassandra.OperationTimedOut: errors={'127.0.0.1': 'Client request timeout. See Session.execute[_async](timeout)'}, last_host=127.0.0.1
  Traceback (most recent call last):
    File "getting_started.py", line 107, in &lt;module&gt;
      example1.insert_data()
    File "getting_started.py", line 86, in insert_data
      self.table_name, "id", "version", "row"
    File "cassandra/cluster.py", line 2405, in cassandra.cluster.Session.prepare
    File "cassandra/cluster.py", line 2402, in cassandra.cluster.Session.prepare
    File "cassandra/cluster.py", line 4062, in cassandra.cluster.ResponseFuture.result
  cassandra.OperationTimedOut: errors={'127.0.0.1': 'Client request timeout. See Session.execute[_async](timeout)'}, last_host=127.0.0.1
  </code></pre>