We are trying to inject millions to data into a table by executing Batches of PreparedStatments.

We found that when we use 'session.execute(batch)', it write more data but very very slow.
However if we use  'session.execute_async(batch)' then its relatively fast but when it reaches certain limit, its fillup the memory (python process)

Our implementation:
Cassandra 3.7.0 cluster  ring with 3 nodes (RedHat, 150GB Disk, 8GB of RAM each)

Python 2.7.12

Anybody know how to reduce the memory use of Cassandra-python driver API specifically for execute_async? Thank you!

===CODE ======================================
      sqlQuery = "INSERT INTO tableV  (id, sample_name, pos, ref_base, var_base) values (?,?,?,?,?)"
       random_numbers_for_strains = random.sample(xrange(1,300), 200)
        random_numbers = random.sample(xrange(1,2000000), 200000)
        totalCounter  = 0
        c = 0
        time_init = time.time()
        for random_number_strain in random_numbers_for_strains:
            sample_name = None
            sample_name = 'sample'+str(random_number_strain)
            cassandraCluster = CassandraCluster.CassandraCluster()
            cluster = cassandraCluster.create_cluster_with_protocol2()
            session = cluster.connect();
            #session.default_timeout = 1800
            preparedStatement = session.prepare(sqlQuery)
            counter = 0
            c = c + 1
            for random_number in random_numbers:

                totalCounter += 1
                if counter == 0 :
                    batch = BatchStatement()

                counter += 1
                if totalCounter % 10000 == 0 :
                    print "Total Count "+ str(totalCounter)

                batch.add(preparedStatement.bind([ uuid.uuid1(), sample_name, random_number, random.choice('GT'), random.choice('AC')]))
                if counter % 50 == 0:
                    batch = None
                    del batch
                    counter = 0
            random_number= None
            del random_number
            preparedStatement = None
            session = None
            del session
            cluster = None
            del cluster
            cassandraCluster = None
            del cassandraCluster
===CODE ======================================

Kind regards,
Rajesh Radhakrishnan

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