contrib/src/main/java/org/apache/apex/malhar/contrib/cassandra/AbstractCassandraTransactionableOutputOperator.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.apex.malhar.contrib.cassandra;

import java.util.Collection;

import javax.annotation.Nonnull;

import org.apache.apex.malhar.lib.db.AbstractBatchTransactionableStoreOutputOperator;

import com.datastax.driver.core.BatchStatement;
import com.datastax.driver.core.PreparedStatement;
import com.datastax.driver.core.Statement;
import com.datastax.driver.core.exceptions.DriverException;
import com.datatorrent.api.Context;
import com.datatorrent.api.Context.OperatorContext;
import com.datatorrent.api.Operator.ActivationListener;

/**
 * <p>
 * Generic Cassandra output adaptor which creates a transaction at the start of window.&nbsp; Subclasses should provide implementation for getting the update statement and setting the statement parameters.  <br/>
 * </p>
 *
 * <p>
 * Executes batch of CQL updates and closes the transaction at the end of the window.
 * Each tuple corresponds to an CQL update statement. The operator groups the updates in a batch
 * and submits them with one call to the database. Batch processing improves performance considerably and also provides atomicity.<br/>
 * The size of a batch is equal to the size of the window.
 * </p>
 *
 * <p>
 * The tuples in a window are stored in check-pointed collection which is cleared in the endWindow().
 * This is needed for the recovery. The operator writes a tuple exactly once in the database, which is why
 * only when all the updates are executed, the transaction is committed in the end window call.
 * </p>
 * @displayName Abstract Cassandra Transactionable Output
 * @category Output
 * @tags cassandra, batch, transactionable
 * @param <T>type of tuple</T>
 * @since 1.0.2
 */
public abstract class AbstractCassandraTransactionableOutputOperator<T> extends AbstractBatchTransactionableStoreOutputOperator<T, CassandraTransactionalStore> implements ActivationListener<Context.OperatorContext>
{
  private transient PreparedStatement updateCommand;

  @Override
  public void activate(OperatorContext context)
  {
    updateCommand = getUpdateCommand();
  }

  /**
   * Gets the statement which insert/update the table in the database.
   *
   * @return the cql statement to update a tuple in the database.
   */
  @Nonnull
  protected abstract PreparedStatement getUpdateCommand();

  /**
   * Sets the parameter of the insert/update statement with values from the tuple.
   *
   * @param tuple     tuple
   * @return statement The statement to execute
   * @throws DriverException
   */
  protected abstract Statement setStatementParameters(PreparedStatement updateCommand, T tuple) throws DriverException;


  @Override
  public void processBatch(Collection<T> tuples)
  {
    BatchStatement batchCommand = store.getBatchCommand();
    for (T tuple: tuples) {
      batchCommand.add(setStatementParameters(updateCommand, tuple));
    }
  }

  @Override
  public void deactivate()
  {
  }
}