/*
* Copyright (c) 2008-2017, Hazelcast, 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.
*/
package com.hazelcast.internal.networking.nio.iobalancer;
import com.hazelcast.internal.networking.nio.MigratableHandler;
import java.util.Set;
/**
* Default {@link MigrationStrategy} for {@link MigratableHandler} instances.
*
* It attempts to trigger a migration if a ratio between least busy and most busy selectors
* exceeds {@link #MIN_MAX_RATIO_MIGRATION_THRESHOLD}.
*
* Once a migration is triggered it tries to find the busiest handler registered in
* {@link LoadImbalance#sourceSelector} which wouldn't cause
* overload of the {@link LoadImbalance#destinationSelector} after a migration.
*
*/
class EventCountBasicMigrationStrategy implements MigrationStrategy {
/**
* You can use this property to tune whether the migration will be attempted at all. The higher the number is
* the more likely the migration will be attempted. Too higher number will result in unnecessary overhead, too
* low number will cause performance degradation due selector imbalance.
*
* Try to schedule a migration if the least busy NioThread receives less events
* then (MIN_MAX_RATIO_MIGRATION_THRESHOLD * no. of events received by the busiest NioThread)
*/
private static final double MIN_MAX_RATIO_MIGRATION_THRESHOLD = 0.8;
/**
* You can use this property to tune a selection process for handler migration. The higher number is the more
* aggressive migration process is.
*/
private static final double MAXIMUM_NO_OF_EVENTS_AFTER_MIGRATION_COEFFICIENT = 0.9;
/**
* Checks if an imbalance was detected in the system
*
* @param imbalance
* @return <code>true</code> if imbalance threshold has been reached and migration should be attempted
*/
@Override
public boolean imbalanceDetected(LoadImbalance imbalance) {
long min = imbalance.minimumEvents;
long max = imbalance.maximumEvents;
if (min == Long.MIN_VALUE || max == Long.MAX_VALUE) {
return false;
}
long lowerBound = (long) (MIN_MAX_RATIO_MIGRATION_THRESHOLD * max);
return min < lowerBound;
}
/**
* Attempt to find a handler to migrate to a new NioThread.
*
* @param imbalance describing a snapshot of NioThread load
* @return the handler to migrate to a new NioThread or null if no handler needs to be migrated.
*/
@Override
public MigratableHandler findHandlerToMigrate(LoadImbalance imbalance) {
Set<? extends MigratableHandler> candidates = imbalance.getHandlersOwnerBy(imbalance.sourceSelector);
long migrationThreshold = (long) ((imbalance.maximumEvents - imbalance.minimumEvents)
* MAXIMUM_NO_OF_EVENTS_AFTER_MIGRATION_COEFFICIENT);
MigratableHandler candidate = null;
long eventCountInSelectedHandler = 0;
for (MigratableHandler handler : candidates) {
long eventCount = imbalance.getLoad(handler);
if (eventCount > eventCountInSelectedHandler) {
if (eventCount < migrationThreshold) {
eventCountInSelectedHandler = eventCount;
candidate = handler;
}
}
}
return candidate;
}
}