HBaseBackedTransactionLogger.java

/**
 * Copyright 2009 The Apache Software Foundation 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.hadoop.hbase.client.transactional;

import java.io.IOException;
import java.util.Random;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.HColumnDescriptor;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.HTableDescriptor;
import org.apache.hadoop.hbase.client.Delete;
import org.apache.hadoop.hbase.client.Get;
import org.apache.hadoop.hbase.client.HBaseAdmin;
import org.apache.hadoop.hbase.client.HTableInterface;
import org.apache.hadoop.hbase.client.HTablePool;
import org.apache.hadoop.hbase.client.Put;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.util.Bytes;

public class HBaseBackedTransactionLogger implements TransactionLogger {

    /** The name of the transaction status table. */
    public static final String TABLE_NAME = "__GLOBAL_TRX_LOG__";

    private static final byte[] INFO_FAMILY = Bytes.toBytes("Info");

    /**
     * Column which holds the transaction status.
     */
    private static final byte[] STATUS_QUALIFIER = Bytes.toBytes("Status");

    /**
     * Create the global transaction table.
     * 
     * @throws IOException
     */
    public static void createTable() throws IOException {
        createTable(HBaseConfiguration.create());
    }

    /**
     * Create the global transaction table with the given configuration.
     * 
     * @param conf
     * @throws IOException
     */
    public static void createTable(final Configuration conf) throws IOException {
        HTableDescriptor tableDesc = new HTableDescriptor(TABLE_NAME);
        tableDesc.addFamily(new HColumnDescriptor(INFO_FAMILY));
        @SuppressWarnings("resource")
		HBaseAdmin admin = new HBaseAdmin(conf);
        if (!admin.tableExists(TABLE_NAME)) {
            admin.createTable(tableDesc);
        }
    }

    private Random random = new Random();
    private HTablePool tablePool = new HTablePool();

    private HTableInterface getTable() {
        return tablePool.getTable(TABLE_NAME);
    }

    @SuppressWarnings("deprecation")
	private void putTable(final HTableInterface t) {
        if (t == null) {
            return;
        }
        try {
			tablePool.putTable(t);
		} catch (IOException e) {
			e.printStackTrace();
		}
    }

    public HBaseBackedTransactionLogger() throws IOException {
        initTable(HBaseConfiguration.create());
    }

    public HBaseBackedTransactionLogger(final Configuration conf) throws IOException {
        initTable(conf);
    }

    private void initTable(final Configuration conf) throws IOException {
        @SuppressWarnings("resource")
		HBaseAdmin admin = new HBaseAdmin(conf);

        if (!admin.tableExists(TABLE_NAME)) {
            throw new RuntimeException("Table not created. Call createTable() first");
        }
    }

    public long createNewTransactionLog() {
        long id;
        TransactionStatus existing;

        do {
            id = random.nextLong();
            try {
                existing = getStatusForTransaction(id);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        } while (existing != null);

        setStatusForTransaction(id, TransactionStatus.PENDING);

        return id;
    }

    public TransactionStatus getStatusForTransaction(final long transactionId) throws IOException {
        HTableInterface table = getTable();
        try {
            Result result = table.get(new Get(getRow(transactionId)));
            if (result == null || result.isEmpty()) {
                return null;
            }
            byte[] statusCell = result.getValue(INFO_FAMILY, STATUS_QUALIFIER);
            if (statusCell == null) {
                throw new RuntimeException("No status cell for row " + transactionId);
            }
            String statusString = Bytes.toString(statusCell);
            return TransactionStatus.valueOf(statusString);

        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            putTable(table);
        }
    }

    private byte[] getRow(final long transactionId) {
        return Bytes.toBytes("" + transactionId);
    }

    public void setStatusForTransaction(final long transactionId, final TransactionStatus status) {
        Put update = new Put(getRow(transactionId));
        update.add(INFO_FAMILY, STATUS_QUALIFIER, HConstants.LATEST_TIMESTAMP, Bytes.toBytes(status.name()));

        HTableInterface table = getTable();
        try {
            table.put(update);
        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            putTable(table);
        }
    }

    public void forgetTransaction(final long transactionId) {
        Delete delete = new Delete(getRow(transactionId));

        HTableInterface table = getTable();
        try {
            table.delete(delete);
        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            putTable(table);
        }
    }

}