/*
* 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.pig.impl.util;
import java.lang.management.ManagementFactory;
import java.lang.management.MemoryNotificationInfo;
import java.lang.management.MemoryPoolMXBean;
import java.lang.management.MemoryType;
import java.lang.ref.WeakReference;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Properties;
import javax.management.Notification;
import javax.management.NotificationEmitter;
import javax.management.NotificationListener;
import javax.management.openmbean.CompositeData;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* This class Tracks the tenured pool and a list of Spillable objects. When memory gets low, this
* class will start requesting Spillable objects to free up memory.
* <p>
* Low memory is defined as more than 50% of the tenured pool being allocated. Spillable objects are
* tracked using WeakReferences so that the objects can be GCed even though this class has a reference
* to them.
*
*/
public class SpillableMemoryManager implements NotificationListener {
private final Log log = LogFactory.getLog(getClass());
LinkedList<WeakReference<Spillable>> spillables = new LinkedList<WeakReference<Spillable>>();
// if we freed at least this much, invoke GC
// (default 40 MB - this can be overridden by user supplied property)
private static long gcActivationSize = 40000000L ;
// spill file size should be at least this much
// (default 5MB - this can be overridden by user supplied property)
private static long spillFileSizeThreshold = 5000000L ;
// this will keep track of memory freed across spills
// and between GC invocations
private static long accumulatedFreeSize = 0L;
// fraction of biggest heap for which we want to get
// "memory usage threshold exceeded" notifications
private static double memoryThresholdFraction = 0.7;
// fraction of biggest heap for which we want to get
// "collection threshold exceeded" notifications
private static double collectionMemoryThresholdFraction = 0.5;
public SpillableMemoryManager() {
((NotificationEmitter)ManagementFactory.getMemoryMXBean()).addNotificationListener(this, null, null);
List<MemoryPoolMXBean> mpbeans = ManagementFactory.getMemoryPoolMXBeans();
MemoryPoolMXBean biggestHeap = null;
long biggestSize = 0;
for (MemoryPoolMXBean b: mpbeans) {
log.debug("Found heap (" + b.getName() +
") of type " + b.getType());
if (b.getType() == MemoryType.HEAP) {
/* Here we are making the leap of faith that the biggest
* heap is the tenured heap
*/
long size = b.getUsage().getMax();
if (size > biggestSize) {
biggestSize = size;
biggestHeap = b;
}
}
}
if (biggestHeap == null) {
throw new RuntimeException("Couldn't find heap");
}
log.debug("Selected heap to monitor (" +
biggestHeap.getName() + ")");
// we want to set both collection and usage threshold alerts to be
// safe. In some local tests after a point only collection threshold
// notifications were being sent though usage threshold notifications
// were sent early on. So using both would ensure that
// 1) we get notified early (though usage threshold exceeded notifications)
// 2) we get notified always when threshold is exceeded (either usage or
// collection)
/* We set the threshold to be 50% of tenured since that is where
* the GC starts to dominate CPU time according to Sun doc */
biggestHeap.setCollectionUsageThreshold((long)(biggestSize * collectionMemoryThresholdFraction));
// we set a higher threshold for usage threshold exceeded notification
// since this is more likely to be effective sooner and we do not
// want to be spilling too soon
biggestHeap.setUsageThreshold((long)(biggestSize * memoryThresholdFraction));
}
public static void configure(Properties properties) {
try {
spillFileSizeThreshold = Long.parseLong(
(String) properties.getProperty("pig.spill.size.threshold") ) ;
gcActivationSize = Long.parseLong(
(String) properties.getProperty("pig.spill.gc.activation.size") ) ;
}
catch (NumberFormatException nfe) {
throw new RuntimeException("Error while converting system configurations" +
"spill.size.threshold, spill.gc.activation.size", nfe) ;
}
}
public void handleNotification(Notification n, Object o) {
CompositeData cd = (CompositeData) n.getUserData();
MemoryNotificationInfo info = MemoryNotificationInfo.from(cd);
// free the amount exceeded over the threshold and then a further half
// so if threshold = heapmax/2, we will be trying to free
// used - heapmax/2 + heapmax/4
long toFree = 0L;
if(n.getType().equals(MemoryNotificationInfo.MEMORY_THRESHOLD_EXCEEDED)) {
long threshold = (long)(info.getUsage().getMax() * memoryThresholdFraction);
toFree = info.getUsage().getUsed() - threshold + (long)(threshold * 0.5);
log.info("low memory handler called (Usage threshold exceeded) " + info.getUsage());
} else { // MEMORY_COLLECTION_THRESHOLD_EXCEEDED CASE
long threshold = (long)(info.getUsage().getMax() * collectionMemoryThresholdFraction);
toFree = info.getUsage().getUsed() - threshold + (long)(threshold * 0.5);
log.info("low memory handler called (Collection threshold exceeded) " + info.getUsage());
}
if (toFree < 0) {
log.debug("low memory handler returning " +
"because there is nothing to free");
return;
}
synchronized(spillables) {
// Walk the list first and remove nulls, otherwise the sort
// takes way too long.
Iterator<WeakReference<Spillable>> i;
for (i = spillables.iterator(); i.hasNext();) {
Spillable s = i.next().get();
if (s == null) {
i.remove();
}
}
Collections.sort(spillables, new Comparator<WeakReference<Spillable>>() {
/**
* We don't lock anything, so this sort may not be stable if a WeakReference suddenly
* becomes null, but it will be close enough.
* Also between the time we sort and we use these spillables, they
* may actually change in size - so this is just best effort
*/
public int compare(WeakReference<Spillable> o1Ref, WeakReference<Spillable> o2Ref) {
Spillable o1 = o1Ref.get();
Spillable o2 = o2Ref.get();
if (o1 == null && o2 == null) {
return 0;
}
if (o1 == null) {
return 1;
}
if (o2 == null) {
return -1;
}
long o1Size = o1.getMemorySize();
long o2Size = o2.getMemorySize();
if (o1Size == o2Size) {
return 0;
}
if (o1Size < o2Size) {
return 1;
}
return -1;
}
});
long estimatedFreed = 0;
boolean invokeGC = false;
for (i = spillables.iterator(); i.hasNext();) {
Spillable s = i.next().get();
// Still need to check for null here, even after we removed
// above, because the reference may have gone bad on us
// since the last check.
if (s == null) {
i.remove();
continue;
}
long toBeFreed = s.getMemorySize();
log.debug("Memorysize = "+toBeFreed+", spillFilesizethreshold = "+spillFileSizeThreshold+", gcactivationsize = "+gcActivationSize);
// Don't keep trying if the rest of files are too small
if (toBeFreed < spillFileSizeThreshold) {
log.debug("spilling small files - getting out of memory handler");
break ;
}
s.spill();
estimatedFreed += toBeFreed;
accumulatedFreeSize += toBeFreed;
// This should significantly reduce the number of small files
// in case that we have a lot of nested bags
if (accumulatedFreeSize > gcActivationSize) {
invokeGC = true;
}
if (estimatedFreed > toFree) {
log.debug("Freed enough space - getting out of memory handler");
invokeGC = true;
break;
}
}
/* Poke the GC again to see if we successfully freed enough memory */
if(invokeGC) {
System.gc();
// now that we have invoked the GC, reset accumulatedFreeSize
accumulatedFreeSize = 0;
}
}
}
/**
* Register a spillable to be tracked. No need to unregister, the tracking will stop
* when the spillable is GCed.
* @param s the spillable to track.
*/
public void registerSpillable(Spillable s) {
synchronized(spillables) {
// Cleaing the entire list is too expensive. Just trim off the front while
// we can.
WeakReference<Spillable> first = spillables.peek();
while (first != null && first.get() == null) {
spillables.remove();
first = spillables.peek();
}
spillables.add(new WeakReference<Spillable>(s));
}
}
}