org.apache.karaf.main.lock.OracleJDBCLock Maven / Gradle / Ivy

Show more of this group Show more artifacts with this name
Show all versions of org.apache.karaf.main
This bundle is the main Karaf launcher. It's responsible of the Karaf startup including the console, branding, etc bootstrap.
There is a newer version: 4.4.6
Show newest version
/*
 * 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.karaf.main.lock;

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import org.apache.felix.utils.properties.Properties;

/**
 * Represents an exclusive lock on a database,
 * used to avoid multiple Karaf instances attempting
 * to become master.
 */
public class OracleJDBCLock extends DefaultJDBCLock {
    
    private static final String MOMENT_COLUMN_DATA_TYPE = "NUMBER(20)";

    public OracleJDBCLock(Properties props) {
        super(props);
    }

    @Override
    Statements createStatements() {
        Statements statements = new Statements();
        statements.setTableName(table);
        statements.setNodeName(clusterName);
        statements.setMomentColumnDataType(MOMENT_COLUMN_DATA_TYPE);
        return statements;
    }
    
    /**
     * When we perform an update on a long lived locked table, Oracle will save
     * a copy of the transaction in it's UNDO table space. Eventually this can
     * cause the UNDO table to become full, disrupting all locks in the DB instance.
     * A select query just touches the table, ensuring we can still read the DB but
     * doesn't add to the UNDO. 
     */
    @Override
    public boolean lock() {
        return aquireLock();
    }
    
    /**
     * When we perform an update on a long lived locked table, Oracle will save
     * a copy of the transaction in it's UNDO table space. Eventually this can
     * cause the UNDO table to become full, disrupting all locks in the DB instance.
     * A select query just touches the table, ensuring we can still read the DB but
     * doesn't add to the UNDO. 
     */
    @Override
    boolean updateLock() {
        return aquireLock();
    }
    
    /**
     * A SELECT FOR UPDATE does not create a database lock when the SELECT FOR UPDATE is performed
     * on an empty selection. So a succesfull call to {@link DefaultJDBCLock#aquireLock()} is not sufficient to 
     * ensure that we are the only one who have acquired the lock.
     */
    @Override
    boolean aquireLock() {
    	return super.aquireLock() && lockAcquiredOnNonEmptySelection();
    }
    
    //Verify that we have a non empty record set.
    private boolean lockAcquiredOnNonEmptySelection() {
        String verifySelectionNotEmpytStatement = statements.getLockVerifySelectionNotEmptyStatement();
        PreparedStatement preparedStatement = null;
        boolean lockAquired = false;
        
        try {
            preparedStatement = getConnection().prepareStatement(verifySelectionNotEmpytStatement);
            preparedStatement.setQueryTimeout(timeout);
            ResultSet rs = preparedStatement.executeQuery();
            if (rs.next()) {
            	lockAquired = rs.getInt(1) > 0;
            } else {
            	LOG.warning("Failed to acquire database lock. Missing database lock record.");
            }
        } catch (Exception e) {
            LOG.warning("Failed to acquire database lock: " + e);
        }finally {
            closeSafely(preparedStatement);
        }        
        return lockAquired;
    }
}