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Building blocks for ClusterMate-based services and servers.
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package com.fasterxml.clustermate.service.store;
import java.util.ArrayList;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.LockSupport;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.fasterxml.clustermate.service.cfg.DeferredDeleteConfig;
import com.fasterxml.clustermate.service.metrics.DeferQueueMetrics;
import com.fasterxml.clustermate.service.metrics.ExternalOperationMetrics;
import com.fasterxml.clustermate.service.util.DecayingAverageCalculator;
import com.fasterxml.storemate.shared.StorableKey;
import com.fasterxml.storemate.shared.TimeMaster;
import com.fasterxml.storemate.store.StorableStore;
import com.fasterxml.storemate.store.StoreOperationSource;
import com.fasterxml.storemate.store.util.SimpleLogThrottler;
/**
* Helper class used for handling deletions asynchronously.
*/
public class DeferredDeleter
implements com.fasterxml.storemate.shared.StartAndStoppable
{
private final Logger LOG = LoggerFactory.getLogger(getClass());
/**
* We may get shit storms of failures, so let's throttle output for possibly
* voluminous errors to 2 per second...
*/
protected final SimpleLogThrottler _throttledLogger = new SimpleLogThrottler(LOG, 500);
protected final StorableStore _entryStore;
protected final ArrayBlockingQueue _deletions;
protected final DecayingAverageCalculator _averages;
protected final TimeMaster _timeMaster;
protected final int _minDeferQLength;
protected final int _maxDeferQLength;
protected final int _targetMaxQueueDelayMicros;
protected final int _maxQueueDelayMsecs;
protected final Thread _deleteThread;
/**
* We will try to estimate maximum queue length to allow, based
* on maximum delay target and average
*/
protected final AtomicInteger _currentMaxQueueLength;
private final AtomicBoolean _active = new AtomicBoolean(true);
/*
/**********************************************************************
/* Life-cycle
/**********************************************************************
*/
public DeferredDeleter(StorableStore entryStore,
DeferredDeleteConfig config)
{
_timeMaster = entryStore.getTimeMaster();
_minDeferQLength = config.minQueueLength;
_maxDeferQLength = config.maxQueueLength;
_targetMaxQueueDelayMicros = 1000 * Math.max(1, (int) config.queueTargetDelayMsecs.getMillis());
// Start with minimum length...
_currentMaxQueueLength = new AtomicInteger(_minDeferQLength);
_maxQueueDelayMsecs = (int) config.queueMaxDelayMsecs.getMillis();
/* We need at least 'maxDefQLength' entries for deferred (unblocking)
* entries; but also up to N extras for blocking. Since we do not
* know for sure N, let's use conservative upper bound of 1000; it's
* much higher than any thread count allocated for deletions.
*/
_deletions = new ArrayBlockingQueue(Math.max(0, _maxDeferQLength) + 1000);
_entryStore = entryStore;
/* We will also try to estimate how long it would take to complete
* given delete operation as deferred deletion; we will ONLY take
* deferrals up to certain maximum delay, after which blocking
* will be needed to give feedback to caller.
* The main idea here is to optimize for normal steady state, during
* which all deletes should ideally be deferred.
*
* Parameters: average over past 100 samples; start with assumption of
* 10 msec per sample (should be way lower -- note: units are in 1024s of
* msecs!); limit variation to factor of 5.0x
*/
_averages = new DecayingAverageCalculator(100, 10 * 1024, 5.0);
_deleteThread = new Thread(new Runnable() {
@Override
public void run() {
try {
processQueue();
} finally {
LOG.info("Deferred-deleter queue update thread ended.");
}
}
});
_deleteThread.setName("DeferredDeleter");
_deleteThread.setDaemon(true);
_deleteThread.start();
}
public static DeferredDeleter nonDeferring(StorableStore entryStore)
{
DeferredDeleteConfig config = new DeferredDeleteConfig();
config.minQueueLength = 0;
config.maxQueueLength = 0;
return new DeferredDeleter(entryStore, config);
}
@Override
public void start() throws Exception {
// we are good, nothing much to do...
}
@Override
public void prepareForStop() throws Exception
{
// not sure what to do now; should we start failing DELETE additions?
// Add latency? Just log?
// ... for now we do... nothing. And hope delete queue drains adequately?
}
@Override
public void stop() throws Exception
{
_active.set(false);
_deleteThread.interrupt();
}
/*
/**********************************************************************
/* Simple API for feeding us
/**********************************************************************
*/
public DeletionResult addDeferredDeletion(StorableKey key, long currentTime)
{
if (_canDefer(currentTime)) {
// no expiration, no Thread to unpark:
final QueuedDeletion del = new QueuedDeletion(key, 0L, null);
if (!_deletions.offer(del)) {
// should never occur but:
return DeletionResult.forQueueFull();
}
return DeletionResult.forDeferred();
}
return addNonDeferredDeletion(key, currentTime);
}
public DeletionResult addNonDeferredDeletion(StorableKey key, long currentTime)
{
Thread currThread = Thread.currentThread();
final QueuedDeletion del = new QueuedDeletion(key,
currentTime+_maxQueueDelayMsecs, currThread);
if (!_deletions.offer(del)) { // should never occur either...
return DeletionResult.forQueueFull();
}
DeletionResult status;
do {
LockSupport.park();
status = del.getStatus();
} while (status == null);
return status;
}
protected boolean _canDefer(long currentTime)
{
if (_maxDeferQLength <= 0) {
return false;
}
return (_deletions.size() < _currentMaxQueueLength.get());
}
/*
/**********************************************************************
/* Method(s) to expose metrics
/**********************************************************************
*/
protected void augmentMetrics(ExternalOperationMetrics deleteMetrics)
{
DeferQueueMetrics q = new DeferQueueMetrics();
q.minLength = _minDeferQLength;
q.maxLength = _maxDeferQLength;
q.currentLength = _deletions.size();
q.maxLengthForDefer = _currentMaxQueueLength.get();
q.delayTargetMsecs = _targetMaxQueueDelayMicros / 1000;
// and then get estimated average per-operation delay (note: is in usecs)
q.estimatedDelayMsecs = (_averages.getCurrentAverage() / 1000.0);
deleteMetrics.queue = q;
}
/*
/**********************************************************************
/* Main processing loop
/**********************************************************************
*/
/* Batch operations are more efficient than individual ones, and this
* even extends to this seemingly trivial case -- based on measurements,
* doing this does speed things up (probably since sync'ed access to
* blocking queue may trigger context switch?)
*/
private final static int CHUNK_SIZE = 10;
protected void processQueue()
{
final ArrayList buffer = new ArrayList(CHUNK_SIZE);
while (_active.get()) {
// Start by bit of draining action, to catch up with backlog
int count;
try {
count = _deletions.drainTo(buffer, CHUNK_SIZE);
if (count == 0) { // but if none found, revert to blocking...
QueuedDeletion del = _deletions.take();
final long nanoStart = System.nanoTime();
if (_delete(del, _timeMaster.currentTimeMillis())) {
long micros = (System.nanoTime() - nanoStart) >> 10;
int newAvg = _averages.addSample((int) micros);
_updateMaxQueue(newAvg);
}
del.wakeUpCaller();
continue;
}
} catch (InterruptedException e) { // most likely means we are done...
continue;
}
final long nanoStart = System.nanoTime();
final long systemTime = _timeMaster.currentTimeMillis();
int okCount = 0;
for (int i = 0; i < count; ++i) {
// only consider actual deletions to count for time estimation purposes
if (_delete(buffer.get(i), systemTime)) {
++okCount;
}
}
if (okCount > 0) {
long micros = ((System.nanoTime() - nanoStart) / okCount) >> 10;
// if we get full chunk, add more weight
int newAvg;
if (count == CHUNK_SIZE) {
newAvg = _averages.addRepeatedSample((int) micros, 2);
} else {
newAvg = _averages.addSample((int) micros);
}
_updateMaxQueue(newAvg);
}
for (int i = 0; i < count; ++i) {
buffer.get(i).wakeUpCaller();
}
buffer.clear();
}
int left = _deletions.size();
if (left > 0) {
LOG.warn("Deferred-deletes queue NOT empty when ending", left);
}
}
// protected to give access to unit tests (ditto for return value)
private int _updateMaxQueue(int newAvgMicros)
{
// first things first: add bit of time for overhead (say, 1/16 == 6.25%)
newAvgMicros += (newAvgMicros >> 4);
// and then calculate max length, given
int len = _targetMaxQueueDelayMicros / newAvgMicros;
if (len > _maxDeferQLength) {
len = _maxDeferQLength;
} else if (len < _minDeferQLength) {
len = _minDeferQLength;
}
//LOG.info("DELETE-defer-length using {} msec estimate -> {}", newAvgMicros/1000.0, len);
_currentMaxQueueLength.set(len);
return len;
}
/**
* @return True if deletion succeeded; used to only include valid timings
* for estimation
*/
private final boolean _delete(QueuedDeletion deletion, long currentTime)
{
// First things first: are we timed out already?
if (deletion.isExpired(currentTime)) {
deletion.setStatus(DeletionResult.forTimeOut());
return false;
}
try {
_entryStore.softDelete(StoreOperationSource.REQUEST, null, deletion.getKey(), true, true);
deletion.setStatus(DeletionResult.forCompleted());
} catch (Throwable t) {
deletion.setFail(t);
return false;
}
return true;
}
}