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SnappyData store based off Pivotal GemFireXD
/*
* Copyright (c) 2010-2015 Pivotal Software, Inc. All rights reserved.
*
* Licensed 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. See accompanying
* LICENSE file.
*/
package wanActiveActive;
import com.gemstone.gemfire.LogWriter;
import com.gemstone.gemfire.cache.CacheClosedException;
import com.gemstone.gemfire.cache.CacheFactory;
import com.gemstone.gemfire.cache.Declarable;
import com.gemstone.gemfire.cache.Region;
import com.gemstone.gemfire.cache.util.GatewayConflictHelper;
import com.gemstone.gemfire.cache.util.GatewayConflictResolver;
import com.gemstone.gemfire.cache.util.TimestampedEntryEvent;
import com.gemstone.gemfire.pdx.PdxInstance;
import java.util.List;
import java.util.Properties;
/**
* Class WANConflictResolver is a GatewayConflictResolver
* provides several alternative methods for resolving conflicts in a WAN configuration
* when multiple sites are modifying the same objects.
* The resolver is installed into the cache through eu-hub/cache.xml and
* us-hub/cache.xml. These determine the type of conflict resolution that
* will be performed. The options are:
*
* use-latest
* merge
* highest-int
*
* use-latest will select to keep the event with the latest timestamp.
* merge will select to merge the values together.
* highest-int will select to keep the event with the highest modificationCount field.
*/
public class WANConflictResolver implements GatewayConflictResolver, Declarable,
Dialog.CloseCallback {
/** Counter tracking the number of conflicting events received */
protected int numberOfConflicts;
Dialog dialog;
private Thread guiUpdateThread;
/** Conflict resolution options */
static enum conflictResolutionEnum { USE_LATEST, MERGE, HIGHEST_INT };
conflictResolutionEnum resolutionType = conflictResolutionEnum.USE_LATEST;
/**
* Initializes this WANConflictResolver.
* @param p The Properties with which to initialize this
* WANConflictResolver
*/
public void init(Properties p) {
String rType = p.getProperty("resolution-type");
if (rType == null) {
System.out.println("WANConflictResolver: server conflict resolution will keep the latest change");
resolutionType = conflictResolutionEnum.USE_LATEST;
} else if (rType.equalsIgnoreCase("use-latest")) {
System.out.println("WANConflictResolver: server conflict resolution will keep the latest change");
resolutionType = conflictResolutionEnum.USE_LATEST;
} else if (rType.equalsIgnoreCase("merge")) {
System.out.println("WANConflictResolver: server conflict resolution will merge conflicting changes");
resolutionType = conflictResolutionEnum.MERGE;
} else if (rType.equalsIgnoreCase("highest-int")) {
System.out.println("WANConflictResolver: server conflict resolution will keep the highest modificationCount");
resolutionType = conflictResolutionEnum.HIGHEST_INT;
}
/** open GUI to show state and conflict count */
String site = p.getProperty("site", "");
this.dialog = new Dialog(site + " conflict resolver", this, true);
this.dialog.open();
this.dialog.setModification("conflict resolver initialized with \"" + rType + "\"");
startGUIUpdateThread();
}
/* (non-Javadoc)
* @see com.gemstone.gemfire.cache.util.GatewayConflictResolver#onEvent(com.gemstone.gemfire.cache.util.TimestampedEntryEvent, com.gemstone.gemfire.cache.util.GatewayConflictHelper)
*/
@Override
public void onEvent(TimestampedEntryEvent event, GatewayConflictHelper helper) {
LogWriter log = CacheFactory.getAnyInstance().getLogger();
if (!event.getOperation().isUpdate()) {
// for things other than updates use the default timestamp and ID based resolution
if (event.getOldTimestamp() > event.getNewTimestamp()) {
helper.disallowEvent();
}
if (event.getOldTimestamp() == event.getNewTimestamp()
&& event.getOldDistributedSystemID() > event.getNewDistributedSystemID()) {
helper.disallowEvent();
}
return;
}
// cache.xml sets the PDX read-serialized attribute so that the conflict resolver
// can work directly with serialized objects.
PdxInstance oldObj = (PdxInstance)event.getOldValue();
PdxInstance newObj = (PdxInstance)event.getNewValue();
// log information about the conflict. This will appear in cacheserver.log
log.info("WANConflictResolver: \nexisting timestamp=" + event.getOldTimestamp()
+ "\nexisting value=" + oldObj
+ "\nproposed timestamp=" + event.getNewTimestamp()
+ "\nproposed value=" + newObj);
switch (this.resolutionType) {
case USE_LATEST:
if (event.getOldTimestamp() > event.getNewTimestamp()) {
log.info("event is older than cached value - disallowing event");
helper.disallowEvent();
}
else if (event.getOldTimestamp() == event.getNewTimestamp()
&& event.getOldDistributedSystemID() != 2) {
/* eu hub always wins if timestamps are the same */
log.info("event has the same timestamp as the cached value but is from US - disallowing event");
helper.disallowEvent();
}
// else {
// log.info("event is newer than the cached value - allowing event");
// }
break;
case MERGE:
// Grab the conflicting event's history and add the current value's change to it.
// This assumes there has been only one conflicting modification. Otherwise we
// would need to do a more thorough job of merging the histories.
String lastChange = Value.getModification(oldObj);
List history = Value.getHistory(newObj);
if (!history.contains(lastChange)) {
log.info("merging existing change '" + lastChange +"' into new value");
history.add(0, lastChange);
PdxInstance newValue = Value.setHistory(newObj, history);
helper.changeEventValue(newValue);
} else {
log.info("new history contains my last known change, so I'm allowing this event");
}
break;
case HIGHEST_INT:
// The value is stored as a PDX serialized object, so we use PDX to access it
int oldInt = Value.getModificationCount(oldObj);
int newInt = Value.getModificationCount(newObj);
if (oldInt > newInt) {
log.info("disallowing event");
helper.disallowEvent();
}
break;
}
this.dialog.setConflictCount(++this.numberOfConflicts);
}
private void startGUIUpdateThread() {
this.guiUpdateThread = new Thread("wanActiveActive GUI update thread") {
public void run() {
while (true) {
try {
Region region = CacheFactory.getAnyInstance().getRegion("/wanActiveActive");
if (region != null) {
PdxInstance serializedValue = (PdxInstance)region.get("MyValue");
if (serializedValue != null) {
dialog.setModification(Value.getModification(serializedValue));
dialog.setHistory(Value.getHistory(serializedValue).toString());
}
}
try { Thread.sleep(2000); } catch (InterruptedException e) { return; }
} catch (CacheClosedException e) {
return;
} catch (RuntimeException e) {
e.printStackTrace();
return;
}
}
}
};
this.guiUpdateThread.setDaemon(true);
this.guiUpdateThread.start();
}
/** This is invoked when the dialog closes. It will cause the server to shut down. */
public void close() {
System.exit(0);
}
}