| /* |
| * Copyright (c) 2011, 2019 Oracle and/or its affiliates. All rights reserved. |
| * |
| * This program and the accompanying materials are made available under the |
| * terms of the Eclipse Public License v. 2.0 which is available at |
| * http://www.eclipse.org/legal/epl-2.0, |
| * or the Eclipse Distribution License v. 1.0 which is available at |
| * http://www.eclipse.org/org/documents/edl-v10.php. |
| * |
| * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause |
| */ |
| |
| // Contributors: |
| // James Sutherland (Oracle) - initial API and implementation |
| package org.eclipse.persistence.descriptors.partitioning; |
| |
| import java.util.ArrayList; |
| import java.util.List; |
| |
| import org.eclipse.persistence.exceptions.QueryException; |
| import org.eclipse.persistence.internal.databaseaccess.Accessor; |
| import org.eclipse.persistence.internal.sessions.AbstractRecord; |
| import org.eclipse.persistence.internal.sessions.AbstractSession; |
| import org.eclipse.persistence.queries.DatabaseQuery; |
| import org.eclipse.persistence.sessions.server.ClientSession; |
| import org.eclipse.persistence.sessions.server.ServerSession; |
| |
| /** |
| * PUBLIC: |
| * RoundRobinPartitioningPolicy sends requests in a round robin fashion to the set of connection pools. |
| * It is for load-balancing read queries across a cluster of database machines. |
| * It requires that the full database be replicated on each machine, so does not support partitioning. |
| * The data should either be read-only, or writes should be replicated on the database. |
| * @author James Sutherland |
| * @since EclipseLink 2.2 |
| */ |
| public class RoundRobinPartitioningPolicy extends ReplicationPartitioningPolicy { |
| |
| protected volatile int currentIndex = 0; |
| |
| protected boolean replicateWrites = false; |
| |
| public RoundRobinPartitioningPolicy() { |
| super(); |
| } |
| |
| public RoundRobinPartitioningPolicy(boolean replicateWrites) { |
| super(); |
| this.replicateWrites = replicateWrites; |
| } |
| |
| public RoundRobinPartitioningPolicy(String... pools) { |
| super(pools); |
| } |
| |
| public RoundRobinPartitioningPolicy(List<String> pools) { |
| super(pools); |
| } |
| |
| /** |
| * PUBLIC: |
| * Return if write queries should be replicated. |
| * This allows for a set of database to be written to and kept in synch, |
| * and have reads load-balanced across the databases. |
| */ |
| public boolean getReplicateWrites() { |
| return replicateWrites; |
| } |
| |
| /** |
| * PUBLIC: |
| * Set if write queries should be replicated. |
| * This allows for a set of database to be written to and kept in synch, |
| * and have reads load-balanced across the databases. |
| */ |
| public void setReplicateWrites(boolean replicateWrites) { |
| this.replicateWrites = replicateWrites; |
| } |
| |
| /** |
| * INTERNAL: |
| * Get a connection from one of the pools in a round robin rotation fashion. |
| */ |
| @Override |
| public List<Accessor> getConnectionsForQuery(AbstractSession session, DatabaseQuery query, AbstractRecord arguments) { |
| if (this.replicateWrites && query.isModifyQuery()) { |
| return super.getConnectionsForQuery(session, query, arguments); |
| } |
| if (session.getPlatform().hasPartitioningCallback()) { |
| // UCP support. |
| session.getPlatform().getPartitioningCallback().setPartitionId(nextIndex()); |
| return null; |
| } |
| List<Accessor> accessors = new ArrayList<>(1); |
| if (session.isClientSession()) { |
| ClientSession client = (ClientSession)session; |
| // If the client session already has a connection for the transaction, then just use it. |
| if (client.hasWriteConnection() && (session.isExclusiveIsolatedClientSession() || session.isInTransaction())) { |
| accessors.add(client.getWriteConnection()); |
| return accessors; |
| } |
| Accessor accessor = nextAccessor((ServerSession)session.getParent(), query); |
| accessors.add(accessor); |
| // Assign a write connection for the duration of the transaction. |
| if (session.isExclusiveIsolatedClientSession() || session.isInTransaction()) { |
| accessor = ((ClientSession)session).addWriteConnection(accessor.getPool().getName(), accessor); |
| } |
| } else if (session.isServerSession()) { |
| Accessor accessor = nextAccessor((ServerSession)session, query); |
| accessors.add(accessor); |
| } else { |
| throw QueryException.partitioningNotSupported(session, query); |
| } |
| return accessors; |
| } |
| |
| /** |
| * INTERNAL: |
| * Return the next pool index to use. |
| */ |
| public int nextIndex() { |
| int index = ++this.currentIndex; |
| if (index >= this.connectionPools.size()) { |
| this.currentIndex = 0; |
| index = 0; |
| } |
| return index; |
| } |
| |
| /** |
| * INTERNAL: |
| * Return the next connection accessor. |
| */ |
| public Accessor nextAccessor(ServerSession session, DatabaseQuery query) { |
| int index = nextIndex(); |
| String poolName = this.connectionPools.get(index); |
| Accessor accessor = acquireAccessor(poolName, session, query, true); |
| // If the connection pools is dead, check the next one. |
| while (accessor == null) { |
| int nextIndex = nextIndex(); |
| poolName = this.connectionPools.get(nextIndex); |
| if (index == nextIndex) { |
| return acquireAccessor(poolName, session, query, false); |
| } |
| accessor = acquireAccessor(poolName, session, query, true); |
| } |
| return accessor; |
| } |
| |
| } |