foundationdb/fdbserver/StorageCache.actor.cpp

/*
 * StorageCache.actor.cpp
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2019 Apple Inc. and the FoundationDB project authors
 *
 * 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.
 */

#include "flow/Arena.h"
#include "fdbclient/FDBOptions.g.h"
#include "fdbclient/NativeAPI.actor.h"
#include "fdbclient/SystemData.h"
#include "fdbserver/Knobs.h"
#include "fdbserver/ServerDBInfo.h"
#include "fdbclient/StorageServerInterface.h"
#include "fdbclient/VersionedMap.h"
#include "fdbclient/KeyRangeMap.h"
#include "fdbclient/Atomic.h"
#include "fdbclient/Notified.h"
#include "fdbserver/LogProtocolMessage.h"
#include "fdbserver/LogSystem.h"
#include "fdbserver/WaitFailure.h"
#include "fdbserver/WorkerInterface.actor.h"
#include "fdbclient/DatabaseContext.h"
#include "fdbclient/NativeAPI.actor.h"
#include "flow/Trace.h"
#include "flow/actorcompiler.h"  // This must be the last #include.


//TODO storageCache server shares quite a bit of storageServer functionality, although simplified
// Need to look into refactoring common code out for better code readability and to avoid duplication

//TODO rename wrong_shard_server error to wrong_cache_server
inline bool canReplyWith(Error e) {
	switch(e.code()) {
		case error_code_transaction_too_old:
		case error_code_future_version:
		case error_code_wrong_shard_server:
		case error_code_cold_cache_server:
		case error_code_process_behind:
		//case error_code_all_alternatives_failed:
			return true;
		default:
			return false;
	};
}
class StorageCacheUpdater;

struct AddingCacheRange : NonCopyable {
	KeyRange keys;
	Future<Void> fetchClient;			// holds FetchKeys() actor
	Promise<Void> fetchComplete;
	Promise<Void> readWrite;

	std::deque< Standalone<VerUpdateRef> > updates;  // during the Fetching phase, mutations with key in keys and version>=(fetchClient's) fetchVersion;

	struct StorageCacheData* server;
	Version transferredVersion;

	enum Phase { WaitPrevious, Fetching, Waiting };

	Phase phase;

	AddingCacheRange( StorageCacheData* server, StorageCacheUpdater* updater, KeyRangeRef const& keys );

	~AddingCacheRange() {
		if( !fetchComplete.isSet() )
			fetchComplete.send(Void());
		if( !readWrite.isSet() )
			readWrite.send(Void());
	}

	void addMutation( Version version, MutationRef const& mutation );

	bool isTransferred() const { return phase == Waiting; }
};

struct CacheRangeInfo : ReferenceCounted<CacheRangeInfo>, NonCopyable {
	AddingCacheRange* adding;
	struct StorageCacheData* readWrite;
	KeyRange keys;
	uint64_t changeCounter;

	CacheRangeInfo(KeyRange keys, AddingCacheRange* adding, StorageCacheData* readWrite)
		: adding(adding), readWrite(readWrite), keys(keys)
	{
	}

	~CacheRangeInfo() {
		delete adding;
	}

	static CacheRangeInfo* newNotAssigned(KeyRange keys) { return new CacheRangeInfo(keys, NULL, NULL); }
	static CacheRangeInfo* newReadWrite(KeyRange keys, StorageCacheData* data) { return new CacheRangeInfo(keys, NULL, data); }
	static CacheRangeInfo* newAdding(StorageCacheData* data, StorageCacheUpdater* updater, KeyRange keys) { return new CacheRangeInfo(keys, new AddingCacheRange(data, updater, keys), NULL); }

	bool isReadable() const { return readWrite!=NULL; }
	bool isAdding() const { return adding!=NULL; }
	bool notAssigned() const { return !readWrite && !adding; }
	bool assigned() const { return readWrite || adding; }
	bool isInVersionedData() const { return readWrite || (adding && adding->isTransferred()); }
	void addMutation( Version version, MutationRef const& mutation );
	bool isFetched() const { return readWrite || ( adding && adding->fetchComplete.isSet() ); }

	const char* debugDescribeState() const {
		if (notAssigned()) return "NotAssigned";
		else if (adding && !adding->isTransferred()) return "AddingFetching";
		else if (adding) return "AddingTransferred";
		else return "ReadWrite";
	}
};

const int VERSION_OVERHEAD = 64 + sizeof(Version) + sizeof(Standalone<VersionUpdateRef>) + //mutationLog, 64b overhead for map
	2 * (64 + sizeof(Version) + sizeof(Reference<VersionedMap<KeyRef,
									   ValueOrClearToRef>::PTreeT>)); //versioned map [ x2 for createNewVersion(version+1) ], 64b overhead for map
static int mvccStorageBytes( MutationRef const& m ) { return VersionedMap<KeyRef, ValueOrClearToRef>::overheadPerItem * 2 + (MutationRef::OVERHEAD_BYTES + m.param1.size() + m.param2.size()) * 2; }

struct FetchInjectionInfo {
	Arena arena;
	vector<VerUpdateRef> changes;
};

struct StorageCacheData {
	typedef VersionedMap<KeyRef, ValueOrClearToRef, FastAllocPTree<KeyRef>> VersionedData;
private:
	// in-memory versioned struct (PTree as of now. Subject to change)
	VersionedData versionedData;
	// in-memory mutationLog that the versionedData contains references to
	// TODO change it to a deque, already contains mutations in version order
	std::map<Version, Standalone<VersionUpdateRef>> mutationLog; // versions (durableVersion, version]

public:
	UID thisServerID; // unique id
	uint16_t index; // server index
	ProtocolVersion logProtocol;
	Reference<ILogSystem> logSystem;
	Key ck; //cacheKey
	Database cx;
	Reference<AsyncVar<ServerDBInfo>> const& db;

	//KeyRangeMap <bool> cachedRangeMap; // map of cached key-ranges
	KeyRangeMap <Reference<CacheRangeInfo>> cachedRangeMap; // map of cached key-ranges
	uint64_t cacheRangeChangeCounter;      // Max( CacheRangeInfo->changecounter )

	// TODO Add cache metrics, such as available memory/in-use memory etc to help dat adistributor assign cached ranges
	//StorageCacheMetrics metrics;

	// newestAvailableVersion[k]
	//   == invalidVersion -> k is unavailable at all versions
	//   <= compactVersion -> k is unavailable at all versions
	//   == v              -> k is readable (from versionedData) @ (oldestVersion,v], and not being updated when version increases
	//   == latestVersion  -> k is readable (from versionedData) @ (oldestVersion,version.get()], and thus stays available when version increases
	CoalescedKeyRangeMap< Version > newestAvailableVersion;

	CoalescedKeyRangeMap< Version > newestDirtyVersion; // Similar to newestAvailableVersion, but includes (only) keys that were only partly available (due to cancelled fetchKeys)

	// The following are in rough order from newest to oldest
	// TODO double check which ones we need for storageCache servers
	Version lastTLogVersion, lastVersionWithData;
	NotifiedVersion version;                 // current version i.e. the max version that can be read from the cache
	NotifiedVersion desiredOldestVersion;    // oldestVersion can be increased to this after compaction
	NotifiedVersion oldestVersion;           // Min version that might be read from the cache

	// TODO not really in use as of now. may need in some failure cases. Revisit and remove if no plausible use
	Future<Void> compactionInProgress;

	FlowLock updateVersionLock;
	FlowLock fetchKeysParallelismLock;
	vector< Promise<FetchInjectionInfo*> > readyFetchKeys;

// TODO do we need otherError here?
	Promise<Void> otherError;
	Promise<Void> coreStarted;

	bool debug_inApplyUpdate;
	double debug_lastValidateTime;

	int64_t versionLag; // An estimate for how many versions it takes for the data to move from the logs to this cache server
	bool behind;

	// TODO double check which ones we need for storageCache servers
	struct Counters {
		CounterCollection cc;
		Counter allQueries, getKeyQueries, getValueQueries, getRangeQueries, finishedQueries, rowsQueried, bytesQueried;
		Counter bytesInput, bytesFetched, mutationBytes;  // Like bytesInput but without MVCC accounting
		Counter mutations, setMutations, clearRangeMutations, atomicMutations;
		Counter updateBatches, updateVersions;
		Counter loops;
		Counter readsRejected;

		//LatencyBands readLatencyBands;

		Counters(StorageCacheData* self)
			: cc("StorageCacheServer", self->thisServerID.toString()),
			getKeyQueries("GetKeyQueries", cc),
			getValueQueries("GetValueQueries",cc),
			getRangeQueries("GetRangeQueries", cc),
			allQueries("QueryQueue", cc),
			finishedQueries("FinishedQueries", cc),
			rowsQueried("RowsQueried", cc),
			bytesQueried("BytesQueried", cc),
			bytesInput("BytesInput", cc),
			bytesFetched("BytesFetched", cc),
			mutationBytes("MutationBytes", cc),
			mutations("Mutations", cc),
			setMutations("SetMutations", cc),
			clearRangeMutations("ClearRangeMutations", cc),
			atomicMutations("AtomicMutations", cc),
			updateBatches("UpdateBatches", cc),
			updateVersions("UpdateVersions", cc),
			loops("Loops", cc),
			readsRejected("ReadsRejected", cc)
		{
			specialCounter(cc, "LastTLogVersion", [self](){ return self->lastTLogVersion; });
			specialCounter(cc, "Version", [self](){ return self->version.get(); });
			specialCounter(cc, "VersionLag", [self](){ return self->versionLag; });
		}
	} counters;

	explicit StorageCacheData(UID thisServerID, uint16_t index, Reference<AsyncVar<ServerDBInfo>> const& db)
		:   versionedData(FastAllocPTree<KeyRef>{std::make_shared<int>(0)}),
			thisServerID(thisServerID), index(index), logProtocol(0), db(db),
			cacheRangeChangeCounter(0),
			lastTLogVersion(0), lastVersionWithData(0),
			compactionInProgress(Void()),
			fetchKeysParallelismLock(SERVER_KNOBS->FETCH_KEYS_PARALLELISM_BYTES),
			debug_inApplyUpdate(false), debug_lastValidateTime(0),
			versionLag(0), behind(false), counters(this)
	{
		version.initMetric(LiteralStringRef("StorageCacheData.Version"), counters.cc.id);
		desiredOldestVersion.initMetric(LiteralStringRef("StorageCacheData.DesriedOldestVersion"), counters.cc.id);
		oldestVersion.initMetric(LiteralStringRef("StorageCacheData.OldestVersion"), counters.cc.id);

		newestAvailableVersion.insert(allKeys, invalidVersion);
		newestDirtyVersion.insert(allKeys, invalidVersion);
		addCacheRange( CacheRangeInfo::newNotAssigned( allKeys ) );
		cx = openDBOnServer(db, TaskPriority::DefaultEndpoint, true, true);
	}

	// Puts the given cacheRange into cachedRangeMap.  The caller is responsible for adding cacheRanges
	//   for all ranges in cachedRangeMap.getAffectedRangesAfterInsertion(newCacheRange->keys)), because these
	//   cacheRanges are invalidated by the call.
	void addCacheRange( CacheRangeInfo* newCacheRange ) {
		ASSERT( !newCacheRange->keys.empty() );
		newCacheRange->changeCounter = ++cacheRangeChangeCounter;
		//TraceEvent(SevDebug, "AddCacheRange", this->thisServerID).detail("KeyBegin", newCacheRange->keys.begin).detail("KeyEnd", newCacheRange->keys.end).
		//detail("State", newCacheRange->isReadable() ? "Readable" : newCacheRange->notAssigned() ? "NotAssigned" : "Adding").detail("Version", this->version.get());
		cachedRangeMap.insert( newCacheRange->keys, Reference<CacheRangeInfo>(newCacheRange) );
	}
	void addMutation(KeyRangeRef const& cachedKeyRange, Version version, MutationRef const& mutation);
	void applyMutation( MutationRef const& m, Arena& arena, VersionedData &data);

	bool isReadable( KeyRangeRef const& keys ) {
		auto cr = cachedRangeMap.intersectingRanges(keys);
		for(auto i = cr.begin(); i != cr.end(); ++i)
			if (!i->value()->isReadable())
				return false;
		return true;
	}

	void checkChangeCounter( uint64_t oldCacheRangeChangeCounter, KeyRef const& key ) {
		if (oldCacheRangeChangeCounter != cacheRangeChangeCounter &&
			cachedRangeMap[key]->changeCounter > oldCacheRangeChangeCounter)
		{
			TEST(true); // CacheRange change during getValueQ
			// TODO: should we throw the cold_cache_server() error here instead?
			throw wrong_shard_server();
		}
	}

	void checkChangeCounter( uint64_t oldCacheRangeChangeCounter, KeyRangeRef const& keys ) {
		if (oldCacheRangeChangeCounter != cacheRangeChangeCounter) {
			auto sh = cachedRangeMap.intersectingRanges(keys);
			for(auto i = sh.begin(); i != sh.end(); ++i)
				if (i->value()->changeCounter > oldCacheRangeChangeCounter) {
					TEST(true); // CacheRange change during range operation
					// TODO: should we throw the cold_cache_server() error here instead?
					throw wrong_shard_server();
				}
		}
	}

	Arena lastArena;
	std::map<Version, Standalone<VersionUpdateRef>> const & getMutationLog() { return mutationLog; }
	std::map<Version, Standalone<VersionUpdateRef>>& getMutableMutationLog() { return mutationLog; }
	VersionedData const& data() const { return versionedData; }
	VersionedData& mutableData() { return versionedData; }

	Standalone<VersionUpdateRef>& addVersionToMutationLog(Version v) {
		// return existing version...
		auto m = mutationLog.find(v);
		if (m != mutationLog.end())
			return m->second;

		// ...or create a new one
		auto& u = mutationLog[v];
		u.version = v;
		if (lastArena.getSize() >= 65536) lastArena = Arena(4096);
		u.arena() = lastArena;
		counters.bytesInput += VERSION_OVERHEAD;
		return u;
	}

	MutationRef addMutationToMutationLog(Standalone<VersionUpdateRef> &mLV, MutationRef const& m){
		counters.bytesInput += mvccStorageBytes(m);
		return mLV.mutations.push_back_deep( mLV.arena(), m );
	}

};
void applyMutation( StorageCacheUpdater* updater, StorageCacheData *data, MutationRef const& mutation, Version version );

/////////////////////////////////// Validation ///////////////////////////////////////
#pragma region Validation
bool validateCacheRange( StorageCacheData::VersionedData::ViewAtVersion const& view, KeyRangeRef range, Version version, UID id, Version minInsertVersion ) {
	// * Nonoverlapping: No clear overlaps a set or another clear, or adjoins another clear.
	// * Old mutations are erased: All items in versionedData.atLatest() have insertVersion() > oldestVersion()

	//TraceEvent(SevDebug, "ValidateRange", id).detail("KeyBegin", range.begin).detail("KeyEnd", range.end).detail("Version", version);
	KeyRef k;
	bool ok = true;
	bool kIsClear = false;
	auto i = view.lower_bound(range.begin);
	if (i != view.begin()) --i;
	for(; i != view.end() && i.key() < range.end; ++i) {
		// TODO revisit this check. there could be nodes in PTree that were inserted, but never updated. their insertVersion thus maybe lower than the current oldest version of the versioned map
		//if (i.insertVersion() <= minInsertVersion)
		//	TraceEvent(SevError,"SCValidateCacheRange",id).detail("IKey", i.key()).detail("Version", version).detail("InsertVersion", i.insertVersion()).detail("MinInsertVersion", minInsertVersion);
		//ASSERT( i.insertVersion() > minInsertVersion );
		if (kIsClear && i->isClearTo() ? i.key() <= k : i.key() < k) {
			TraceEvent(SevError,"SCInvalidRange",id).detail("Key1", k).detail("Key2", i.key()).detail("Version", version);
			ok = false;
		}
		//ASSERT( i.key() >= k );
		kIsClear = i->isClearTo();
		k = kIsClear ? i->getEndKey() : i.key();
	}
	return ok;
}

void validate(StorageCacheData* data, bool force = false) {
	try {
		if (force || (EXPENSIVE_VALIDATION)) {
			data->newestAvailableVersion.validateCoalesced();
			data->newestDirtyVersion.validateCoalesced();

			for(auto range = data->cachedRangeMap.ranges().begin(); range != data->cachedRangeMap.ranges().end(); ++range) {
				ASSERT( range->value()->keys == range->range() );
				ASSERT( !range->value()->keys.empty() );
			}

			for(auto range = data->cachedRangeMap.ranges().begin(); range != data->cachedRangeMap.ranges().end(); ++range)
				if (range->value()->isReadable()) {
					auto ar = data->newestAvailableVersion.intersectingRanges(range->range());
					for(auto a = ar.begin(); a != ar.end(); ++a)
						ASSERT( a->value() == latestVersion );
				}

			// * versionedData contains versions [oldestVersion.get(), version.get()].  It might also contain later versions if applyUpdate is on the stack.
			ASSERT( data->data().getOldestVersion() == data->oldestVersion.get() );
			ASSERT( data->data().getLatestVersion() == data->version.get() || data->data().getLatestVersion() == data->version.get()+1 || (data->debug_inApplyUpdate && data->data().getLatestVersion() > data->version.get()) );

			auto latest = data->data().atLatest();

			latest.validate();
			validateCacheRange(latest, allKeys, data->version.get(), data->thisServerID, data->oldestVersion.get());

			data->debug_lastValidateTime = now();
			//TraceEvent(SevDebug, "SCValidationDone", data->thisServerID).detail("LastValidTime", data->debug_lastValidateTime);
		}
	} catch (...) {
		TraceEvent(SevError, "SCValidationFailure", data->thisServerID).detail("LastValidTime", data->debug_lastValidateTime);
		throw;
	}
}
#pragma endregion

///////////////////////////////////// Queries /////////////////////////////////
#pragma region Queries
ACTOR Future<Version> waitForVersion( StorageCacheData* data, Version version ) {
	// This could become an Actor transparently, but for now it just does the lookup
	if (version == latestVersion)
		version = std::max(Version(1), data->version.get());
	if (version < data->oldestVersion.get() || version <= 0) throw transaction_too_old();
	else if (version <= data->version.get())
		return version;

	if(data->behind && version > data->version.get()) {
		throw process_behind();
	}

	if(deterministicRandom()->random01() < 0.001)
		TraceEvent("WaitForVersion1000x");
	choose {
		when ( wait( data->version.whenAtLeast(version) ) ) {
			//FIXME: A bunch of these can block with or without the following delay 0.
			//wait( delay(0) );  // don't do a whole bunch of these at once
			if (version < data->oldestVersion.get()) throw transaction_too_old();
			return version;
		}
		when ( wait( delay( SERVER_KNOBS->FUTURE_VERSION_DELAY ) ) ) {
			if(deterministicRandom()->random01() < 0.001)
				TraceEvent(SevWarn, "CacheServerFutureVersion1000x", data->thisServerID)
					.detail("Version", version)
					.detail("MyVersion", data->version.get())
					.detail("ServerID", data->thisServerID);
			throw future_version();
		}
	}
}

ACTOR Future<Version> waitForVersionNoTooOld( StorageCacheData* data, Version version ) {
	// This could become an Actor transparently, but for now it just does the lookup
	if (version == latestVersion)
		version = std::max(Version(1), data->version.get());
	if (version <= data->version.get())
		return version;
	choose {
		when ( wait( data->version.whenAtLeast(version) ) ) {
			return version;
		}
		when ( wait( delay( SERVER_KNOBS->FUTURE_VERSION_DELAY ) ) ) {
			if(deterministicRandom()->random01() < 0.001)
				TraceEvent(SevWarn, "CacheServerFutureVersion1000x", data->thisServerID)
					.detail("Version", version)
					.detail("MyVersion", data->version.get())
					.detail("ServerID", data->thisServerID);
			throw future_version();
		}
	}
}

ACTOR Future<Void> getValueQ( StorageCacheData* data, GetValueRequest req ) {
	state int64_t resultSize = 0;

	try {
		++data->counters.getValueQueries;
		++data->counters.allQueries;
		//++data->readQueueSizeMetric;
		//TODO later
		//data->maxQueryQueue = std::max<int>( data->maxQueryQueue, data->counters.allQueries.getValue() - data->counters.finishedQueries.getValue());

		// Active load balancing runs at a very high priority (to obtain accurate queue lengths)
		// so we need to downgrade here

		//TODO what's this?
		wait( delay(0, TaskPriority::DefaultEndpoint) );

		if( req.debugID.present() )
			g_traceBatch.addEvent("GetValueDebug", req.debugID.get().first(), "getValueQ.DoRead"); //.detail("TaskID", g_network->getCurrentTask());

		state Optional<Value> v;
		state Version version = wait( waitForVersion( data, req.version ) );
		if( req.debugID.present() )
			g_traceBatch.addEvent("GetValueDebug", req.debugID.get().first(), "getValueQ.AfterVersion"); //.detail("TaskID", g_network->getCurrentTask());

		state uint64_t changeCounter = data->cacheRangeChangeCounter;

		if (data->cachedRangeMap[req.key]->notAssigned()) {
			//TraceEvent(SevWarn, "WrongCacheServer", data->thisServerID).detail("Key", req.key).detail("ReqVersion", req.version).detail("DataVersion", data->version.get()).detail("In", "getValueQ");
			throw wrong_shard_server();
		} else if (!data->cachedRangeMap[req.key]->isReadable()) {
			//TraceEvent(SevWarn, "ColdCacheServer", data->thisServerID).detail("Key", req.key).detail("IsAdding", data->cachedRangeMap[req.key]->isAdding())
			//	.detail("ReqVersion", req.version).detail("DataVersion", data->version.get()).detail("In", "getValueQ");
			throw future_version();
		}

		state int path = 0;
		auto i = data->data().at(version).lastLessOrEqual(req.key);
		if (i && i->isValue() && i.key() == req.key) {
			v = (Value)i->getValue();
			path = 1;
			// TODO: do we need to check changeCounter here?
			data->checkChangeCounter(changeCounter, req.key);
		}

		// FIXME: enable when debugMutation is active
		//debugMutation("CacheGetValue", version, MutationRef(MutationRef::DebugKey, req.key, v.present()?v.get():LiteralStringRef("<null>")));
		//debugMutation("CacheGetPath", version, MutationRef(MutationRef::DebugKey, req.key, path==0?LiteralStringRef("0"):path==1?LiteralStringRef("1"):LiteralStringRef("2")));

		if (v.present()) {
			++data->counters.rowsQueried;
			resultSize = v.get().size();
			data->counters.bytesQueried += resultSize;
			//TraceEvent(SevDebug, "SCGetValueQPresent", data->thisServerID).detail("ResultSize",resultSize).detail("Version", version).detail("ReqKey",req.key).detail("Value",v);
		}

		if( req.debugID.present() )
			g_traceBatch.addEvent("GetValueDebug", req.debugID.get().first(), "getValueQ.AfterRead"); //.detail("TaskID", g_network->getCurrentTask());

		GetValueReply reply(v, true);
		req.reply.send(reply);
	} catch (Error& e) {
		//TraceEvent(SevWarn, "SCGetValueQError", data->thisServerID).detail("Code",e.code()).detail("ReqKey",req.key)
		//	.detail("ReqVersion", req.version).detail("DataVersion", data->version.get());
		if(!canReplyWith(e))
			throw;
		req.reply.sendError(e);
	}

	++data->counters.finishedQueries;
	//--data->readQueueSizeMetric;
	//if(data->latencyBandConfig.present()) {
	//	int maxReadBytes = data->latencyBandConfig.get().readConfig.maxReadBytes.orDefault(std::numeric_limits<int>::max());
	//	data->counters.readLatencyBands.addMeasurement(timer() - req.requestTime(), resultSize > maxReadBytes);
	//}

	return Void();
};

GetKeyValuesReply readRange(StorageCacheData* data, Version version, KeyRangeRef range, int limit, int* pLimitBytes) {
	GetKeyValuesReply result;
	StorageCacheData::VersionedData::ViewAtVersion view = data->data().at(version);
	StorageCacheData::VersionedData::iterator vCurrent = view.end();
	KeyRef readBegin;
	KeyRef rangeBegin = range.begin;
	KeyRef rangeEnd = range.end;
	//printf("\nSCReadRange\n");

	// if (limit >= 0) we are reading forward, else backward
	if (limit >= 0) {
		//We might care about a clear beginning before start that runs into range
		vCurrent = view.lastLessOrEqual(rangeBegin);
		if (vCurrent && vCurrent->isClearTo() && vCurrent->getEndKey() > rangeBegin)
			readBegin = vCurrent->getEndKey();
		else
			readBegin = rangeBegin;

		vCurrent = view.lower_bound(readBegin);
		ASSERT(!vCurrent || vCurrent.key() >= readBegin);
		if (vCurrent) {
			auto b = vCurrent;
			--b;
			ASSERT(!b || b.key() < readBegin);
		}
		int accumulatedBytes = 0;
		while (vCurrent && vCurrent.key() < rangeEnd && limit > 0 && accumulatedBytes < *pLimitBytes) {
			if (!vCurrent->isClearTo()) {
				result.data.push_back_deep(result.arena, KeyValueRef(vCurrent.key(), vCurrent->getValue()));
				accumulatedBytes += sizeof(KeyValueRef) + result.data.end()[-1].expectedSize();
				--limit;
			}
			++vCurrent;
		}
	} else { // reverse readRange
		vCurrent = view.lastLess(rangeEnd);

		// A clear might extend all the way to range.end
		if (vCurrent && vCurrent->isClearTo() && vCurrent->getEndKey() >= rangeEnd) {
			readEnd = vCurrent.key();
			--vCurrent;
		} else {
			readEnd = rangeEnd;
		}
		ASSERT(!vCurrent || vCurrent.key() < readEnd);
		if (vCurrent) {
			auto b = vCurrent;
			--b;
			ASSERT(!b || b.key() >= readEnd);
		}
		int accumulatedBytes = 0;
		while (vCurrent && vCurrent.key() >= rangeEnd && limit > 0 && accumulatedBytes < *pLimitBytes) {
			if (!vCurrent->isClearTo()) {
				result.data.push_back_deep(result.arena, KeyValueRef(vCurrent.key(), vCurrent->getValue()));
				accumulatedBytes += sizeof(KeyValueRef) + result.data.end()[-1].expectedSize();
				--limit;
			}
			--vCurrent;
		}
	}

	*pLimitBytes -= accumulatedBytes;
	ASSERT(result.data.size() == 0 || *pLimitBytes + result.data.end()[-1].expectedSize() + sizeof(KeyValueRef) > 0);
	result.more = limit == 0 || *pLimitBytes <= 0; // FIXME: Does this have to be exact?
	result.version = version;
	result.cached = true;
	return result;
}

Key findKey( StorageCacheData* data, KeySelectorRef sel, Version version, KeyRange range, int* pOffset)
// Attempts to find the key indicated by sel in the data at version, within range.
// Precondition: selectorInRange(sel, range)
// If it is found, offset is set to 0 and a key is returned which falls inside range.
// If the search would depend on any key outside range OR if the key selector offset is too large (range read returns too many bytes), it returns either
//   a negative offset and a key in [range.begin, sel.getKey()], indicating the key is (the first key <= returned key) + offset, or
//   a positive offset and a key in (sel.getKey(), range.end], indicating the key is (the first key >= returned key) + offset-1
// The range passed in to this function should specify a cacheRange.  If range.begin is repeatedly not the beginning of a cacheRange, then it is possible to get stuck looping here
{
	ASSERT( version != latestVersion );
	ASSERT( selectorInRange(sel, range) && version >= data->oldestVersion.get());

	// Count forward or backward distance items, skipping the first one if it == key and skipEqualKey
	bool forward = sel.offset > 0;                  // If forward, result >= sel.getKey(); else result <= sel.getKey()
	int sign = forward ? +1 : -1;
	bool skipEqualKey = sel.orEqual == forward;
	int distance = forward ? sel.offset : 1-sel.offset;

	//Don't limit the number of bytes if this is a trivial key selector (there will be at most two items returned from the read range in this case)
	int maxBytes;
	if (sel.offset <= 1 && sel.offset >= 0)
		maxBytes = std::numeric_limits<int>::max();
	else
		maxBytes = BUGGIFY ? SERVER_KNOBS->BUGGIFY_LIMIT_BYTES : SERVER_KNOBS->STORAGE_LIMIT_BYTES;

	GetKeyValuesReply rep = readRange( data, version,
									   forward ? KeyRangeRef(sel.getKey(), range.end) : KeyRangeRef(range.begin, keyAfter(sel.getKey())),
									   (distance + skipEqualKey)*sign, &maxBytes );
	bool more = rep.more && rep.data.size() != distance + skipEqualKey;

	//If we get only one result in the reverse direction as a result of the data being too large, we could get stuck in a loop
	if(more && !forward && rep.data.size() == 1) {
		TEST(true); //Reverse key selector returned only one result in range read
		maxBytes = std::numeric_limits<int>::max();
		GetKeyValuesReply rep2 = readRange( data, version, KeyRangeRef(range.begin, keyAfter(sel.getKey())), -2, &maxBytes );
		rep = rep2;
		more = rep.more && rep.data.size() != distance + skipEqualKey;
		ASSERT(rep.data.size() == 2 || !more);
	}

	int index = distance-1;
	if (skipEqualKey && rep.data.size() && rep.data[0].key == sel.getKey() )
		++index;

	if (index < rep.data.size()) {
		*pOffset = 0;
		return rep.data[ index ].key;
	} else {
		// FIXME: If range.begin=="" && !forward, return success?
		*pOffset = index - rep.data.size() + 1;
		if (!forward) *pOffset = -*pOffset;

		if (more) {
			TEST(true); // Key selector read range had more results

			ASSERT(rep.data.size());
			Key returnKey = forward ? keyAfter(rep.data.back().key) : rep.data.back().key;

			//This is possible if key/value pairs are very large and only one result is returned on a last less than query
			//SOMEDAY: graceful handling of exceptionally sized values
			ASSERT(returnKey != sel.getKey());

			return returnKey;
		} else
			return forward ? range.end : range.begin;
	}
}

KeyRange getCachedKeyRange( StorageCacheData* data, const KeySelectorRef& sel )
// Returns largest range that is cached on this server and selectorInRange(sel, range) or wrong_shard_server if no such range exists
{
	auto i = sel.isBackward() ? data->cachedRangeMap.rangeContainingKeyBefore( sel.getKey() ) :
		data->cachedRangeMap.rangeContaining( sel.getKey() );

	//TraceEvent(SevDebug, "SCGetCachedKeyRange", data->thisServerID).detail("SelKey", sel.getKey()).detail("Begin", i->range().begin).detail("End", i->range().end).detail("Value", i->value()->debugDescribeState());
	if (i->value()->notAssigned())
		throw wrong_shard_server();
	else if (!i->value()->isReadable())
		throw future_version();

	ASSERT( selectorInRange(sel, i->range()) );
	return i->range();
}

ACTOR Future<Void> getKeyValues( StorageCacheData* data, GetKeyValuesRequest req )
// Throws a wrong_shard_server if the keys in the request or result depend on data outside this server OR if a large selector offset prevents
// all data from being read in one range read
{
	state int64_t resultSize = 0;

	++data->counters.getRangeQueries;
	++data->counters.allQueries;
	//printf("\nSCGetKeyValues\n");
	//++data->readQueueSizeMetric;
	//data->maxQueryQueue = std::max<int>( data->maxQueryQueue, data->counters.allQueries.getValue() - data->counters.finishedQueries.getValue());

	// Active load balancing runs at a very high priority (to obtain accurate queue lengths)
	// so we need to downgrade here
	TaskPriority taskType = TaskPriority::DefaultEndpoint;
	if (SERVER_KNOBS->FETCH_KEYS_LOWER_PRIORITY && req.isFetchKeys) {
		taskType = TaskPriority::FetchKeys;
	// } else if (false) {
	// 	// Placeholder for up-prioritizing fetches for important requests
	// 	taskType = TaskPriority::DefaultDelay;
	}
	wait( delay(0, taskType) );

	try {
		if( req.debugID.present() )
			g_traceBatch.addEvent("TransactionDebug", req.debugID.get().first(), "storagecache.getKeyValues.Before");
		state Version version = wait( waitForVersion( data, req.version ) );

		state uint64_t changeCounter = data->cacheRangeChangeCounter;

		state KeyRange cachedKeyRange = getCachedKeyRange( data, req.begin );

		//TraceEvent(SevDebug, "SCGetKeyValues1", data->thisServerID).detail("Begin", req.begin.toString()).detail("End", req.end.toString()).detail("Version", version).
		//	detail("CacheRangeBegin", cachedKeyRange.begin).detail("CacheRangeEnd", cachedKeyRange.end);

		if( req.debugID.present() )
			g_traceBatch.addEvent("TransactionDebug", req.debugID.get().first(), "storagecache.getKeyValues.AfterVersion");
		//.detail("CacheRangeBegin", cachedKeyRange.begin).detail("CacheRangeEnd", cachedKeyRange.end);

		if ( !selectorInRange(req.end, cachedKeyRange) && !(req.end.isFirstGreaterOrEqual() && req.end.getKey() == cachedKeyRange.end) ) {
			TraceEvent(SevDebug, "WrongCacheRangeServer1", data->thisServerID).detail("Begin", req.begin.toString()).detail("End", req.end.toString()).detail("Version", version).
			detail("CacheRangeBegin", cachedKeyRange.begin).detail("CacheRangeEnd", cachedKeyRange.end).detail("In", "getKeyValues>checkShardExtents");
			throw wrong_shard_server();
		}

		state int offset1;
		state int offset2;
		state Key begin = req.begin.isFirstGreaterOrEqual() ? req.begin.getKey() : findKey( data, req.begin, version, cachedKeyRange, &offset1 );
		state Key end = req.end.isFirstGreaterOrEqual() ? req.end.getKey() : findKey( data, req.end, version, cachedKeyRange, &offset2 );
		if( req.debugID.present() )
			g_traceBatch.addEvent("TransactionDebug", req.debugID.get().first(), "storagecache.getKeyValues.AfterKeys");
		//.detail("Off1",offset1).detail("Off2",offset2).detail("ReqBegin",req.begin.getKey()).detail("ReqEnd",req.end.getKey());

		// Offsets of zero indicate begin/end keys in this cachedKeyRange, which obviously means we can answer the query
		// An end offset of 1 is also OK because the end key is exclusive, so if the first key of the next cachedKeyRange is the end the last actual key returned must be from this cachedKeyRange.
		// A begin offset of 1 is also OK because then either begin is past end or equal to end (so the result is definitely empty)
		if ((offset1 && offset1!=1) || (offset2 && offset2!=1)) {
			TEST(true);  // wrong_cache_server due to offset
			// We could detect when offset1 takes us off the beginning of the database or offset2 takes us off the end, and return a clipped range rather
			// than an error (since that is what the NativeAPI.getRange will do anyway via its "slow path"), but we would have to add some flags to the response
			// to encode whether we went off the beginning and the end, since it needs that information.
			TraceEvent(SevDebug, "WrongCacheRangeServer2", data->thisServerID).detail("Begin", req.begin.toString()).detail("End", req.end.toString()).detail("Version", version).
			detail("CacheRangeBegin", cachedKeyRange.begin).detail("CacheRangeEnd", cachedKeyRange.end).detail("In", "getKeyValues>checkOffsets").
			detail("BeginKey", begin).detail("EndKey", end).detail("BeginOffset", offset1).detail("EndOffset", offset2);
			throw wrong_shard_server();
		}
		//TraceEvent(SevDebug, "SCGetKeyValues", data->thisServerID).detail("Begin", req.begin.toString()).detail("End", req.end.toString()).detail("Version", version).
		//	detail("CacheRangeBegin", cachedKeyRange.begin).detail("CacheRangeEnd", cachedKeyRange.end).detail("In", "getKeyValues>checkOffsets").
		//	detail("BeginKey", begin).detail("EndKey", end).detail("BeginOffset", offset1).detail("EndOffset", offset2);

		if (begin >= end) {
			if( req.debugID.present() )
				g_traceBatch.addEvent("TransactionDebug", req.debugID.get().first(), "storagecache.getKeyValues.Send");
			//.detail("Begin",begin).detail("End",end);

			GetKeyValuesReply none;
			none.version = version;
			none.more = false;
			data->checkChangeCounter( changeCounter, KeyRangeRef( std::min<KeyRef>(req.begin.getKey(), req.end.getKey()), std::max<KeyRef>(req.begin.getKey(), req.end.getKey()) ) );
			req.reply.send( none );
		} else {
			state int remainingLimitBytes = req.limitBytes;

			GetKeyValuesReply _r = readRange(data, version, KeyRangeRef(begin, end), req.limit, &remainingLimitBytes);
			GetKeyValuesReply r = _r;

			if( req.debugID.present() )
				g_traceBatch.addEvent("TransactionDebug", req.debugID.get().first(), "storagecache.getKeyValues.AfterReadRange");
			data->checkChangeCounter( changeCounter, KeyRangeRef( std::min<KeyRef>(begin, std::min<KeyRef>(req.begin.getKey(), req.end.getKey())), std::max<KeyRef>(end, std::max<KeyRef>(req.begin.getKey(), req.end.getKey())) ) );
			//.detail("Begin",begin).detail("End",end).detail("SizeOf",r.data.size());
			if (EXPENSIVE_VALIDATION) {
				for (int i = 0; i < r.data.size(); i++)
					ASSERT(r.data[i].key >= begin && r.data[i].key < end);
				ASSERT(r.data.size() <= std::abs(req.limit));
			}

			req.reply.send( r );

			resultSize = req.limitBytes - remainingLimitBytes;
			data->counters.bytesQueried += resultSize;
			data->counters.rowsQueried += r.data.size();
		}
	} catch (Error& e) {
		TraceEvent(SevWarn, "SCGetKeyValuesError", data->thisServerID).detail("Code",e.code()).detail("ReqBegin", req.begin.getKey()).detail("ReqEnd", req.end.getKey())
			.detail("ReqVersion", req.version).detail("DataVersion", data->version.get());
		if(!canReplyWith(e))
			throw;
		req.reply.sendError(e);
	}

	++data->counters.finishedQueries;

	return Void();
}

ACTOR Future<Void> getKey( StorageCacheData* data, GetKeyRequest req ) {
	state int64_t resultSize = 0;

	++data->counters.getKeyQueries;
	++data->counters.allQueries;

	//printf("\nSCGetKey\n");
	// Active load balancing runs at a very high priority (to obtain accurate queue lengths)
	// so we need to downgrade here
	wait( delay(0, TaskPriority::DefaultEndpoint) );

	try {
		state Version version = wait( waitForVersion( data, req.version ) );
		state uint64_t changeCounter = data->cacheRangeChangeCounter;
		state KeyRange cachedKeyRange = getCachedKeyRange( data, req.sel );

		state int offset;
		Key k = findKey( data, req.sel, version, cachedKeyRange, &offset );

		data->checkChangeCounter( changeCounter, KeyRangeRef( std::min<KeyRef>(req.sel.getKey(), k), std::max<KeyRef>(req.sel.getKey(), k) ) );

		KeySelector updated;
		if (offset < 0)
			updated = firstGreaterOrEqual(k)+offset;  // first thing on this cacheRange OR (large offset case) smallest key retrieved in range read
		else if (offset > 0)
			updated = firstGreaterOrEqual(k)+offset-1;	// first thing on next cacheRange OR (large offset case) keyAfter largest key retrieved in range read
		else
			updated = KeySelectorRef(k,true,0); //found

		resultSize = k.size();
		data->counters.bytesQueried += resultSize;
		++data->counters.rowsQueried;

		GetKeyReply reply(updated, true);
		req.reply.send(reply);
	}
	catch (Error& e) {
		if (e.code() == error_code_wrong_shard_server) TraceEvent("SCWrongCacheRangeServer").detail("In","getKey");
		if (e.code() == error_code_future_version) TraceEvent("SCColdCacheRangeServer").detail("In","getKey");
		if(!canReplyWith(e))
			throw;
		req.reply.sendError(e);
	}

	++data->counters.finishedQueries;

	return Void();
}

#pragma endregion

bool expandMutation( MutationRef& m, StorageCacheData::VersionedData const& data, KeyRef eagerTrustedEnd, Arena& ar ) {
	// After this function call, m should be copied into an arena immediately (before modifying data, cacheRanges, or eager)
	if (m.type == MutationRef::ClearRange) {
		// Expand the clear
		const auto& d = data.atLatest();

		// If another clear overlaps the beginning of this one, engulf it
		auto i = d.lastLess(m.param1);
		if (i && i->isClearTo() && i->getEndKey() >= m.param1)
			m.param1 = i.key();

		// If another clear overlaps the end of this one, engulf it; otherwise expand
		i = d.lastLessOrEqual(m.param2);
		if (i && i->isClearTo() && i->getEndKey() >= m.param2) {
			m.param2 = i->getEndKey();
		} else {
			// Expand to the next set or clear (from storage or latestVersion), and if it
			// is a clear, engulf it as well
			i = d.lower_bound(m.param2);
			// TODO check if the following is correct
			KeyRef endKey = eagerTrustedEnd;
			if (!i || endKey < i.key())
				m.param2 = endKey;
			else if (i->isClearTo())
				m.param2 = i->getEndKey();
			else
				m.param2 = i.key();
		}
	}
	else if (m.type != MutationRef::SetValue && (m.type)) {

		Optional<StringRef> oldVal;
		auto it = data.atLatest().lastLessOrEqual(m.param1);
		if (it != data.atLatest().end() && it->isValue() && it.key() == m.param1)
			oldVal = it->getValue();
		else if (it != data.atLatest().end() && it->isClearTo() && it->getEndKey() > m.param1) {
			TEST(true); // Atomic op right after a clear.
		}

		switch(m.type) {
		case MutationRef::AddValue:
			m.param2 = doLittleEndianAdd(oldVal, m.param2, ar);
			break;
		case MutationRef::And:
			m.param2 = doAnd(oldVal, m.param2, ar);
			break;
		case MutationRef::Or:
			m.param2 = doOr(oldVal, m.param2, ar);
			break;
		case MutationRef::Xor:
			m.param2 = doXor(oldVal, m.param2, ar);
			break;
		case MutationRef::AppendIfFits:
			m.param2 = doAppendIfFits(oldVal, m.param2, ar);
			break;
		case MutationRef::Max:
			m.param2 = doMax(oldVal, m.param2, ar);
			break;
		case MutationRef::Min:
			m.param2 = doMin(oldVal, m.param2, ar);
			break;
		case MutationRef::ByteMin:
			m.param2 = doByteMin(oldVal, m.param2, ar);
			break;
		case MutationRef::ByteMax:
			m.param2 = doByteMax(oldVal, m.param2, ar);
			break;
		case MutationRef::MinV2:
			m.param2 = doMinV2(oldVal, m.param2, ar);
			break;
		case MutationRef::AndV2:
			m.param2 = doAndV2(oldVal, m.param2, ar);
			break;
		case MutationRef::CompareAndClear:
			if (oldVal.present() && m.param2 == oldVal.get()) {
				m.type = MutationRef::ClearRange;
				m.param2 = keyAfter(m.param1, ar);
				return expandMutation(m, data, eagerTrustedEnd, ar);
			}
			return false;
		}
		m.type = MutationRef::SetValue;
	}

	return true;
}

// Applies a write mutation (SetValue or ClearRange) to the in-memory versioned data structure
void StorageCacheData::applyMutation( MutationRef const& m, Arena& arena, StorageCacheData::VersionedData &data ) {
	// m is expected to be in arena already
	// Clear split keys are added to arena

	if (m.type == MutationRef::SetValue) {
		auto prev = data.atLatest().lastLessOrEqual(m.param1);
		if (prev && prev->isClearTo() && prev->getEndKey() > m.param1) {
			ASSERT( prev.key() <= m.param1 );
			KeyRef end = prev->getEndKey();
			// TODO double check if the insert version of the previous clear needs to be preserved for the "left half",
			// insert() invalidates prev, so prev.key() is not safe to pass to it by reference
			data.insert( KeyRef(prev.key()), ValueOrClearToRef::clearTo( m.param1 ), prev.insertVersion() );  // overwritten by below insert if empty
			//TraceEvent(SevDebug, "ApplyMutationClearTo")
			//.detail("Key1", prev.key())
			//.detail("Key2",m.param1)
			//.detail("Version1", prev.insertVersion());
			KeyRef nextKey = keyAfter(m.param1, arena);
			if ( end != nextKey ) {
				ASSERT( end > nextKey );
				// TODO double check if it's okay to let go of the the insert version of the "right half"
				// FIXME: This copy is technically an asymptotic problem, definitely a waste of memory (copy of keyAfter is a waste, but not asymptotic)
				data.insert( nextKey, ValueOrClearToRef::clearTo( KeyRef(arena, end) ) );
				//TraceEvent(SevDebug, "ApplyMutationClearTo2")
				//.detail("K1", nextKey)
				//.detail("K2", end)
				//.detail("V", data.latestVersion);
			}
		}
		data.insert( m.param1, ValueOrClearToRef::value(m.param2) );
		//TraceEvent(SevDebug, "ApplyMutation")
		//	.detail("Key", m.param1)
		//	.detail("Value",m.param2)
		//	.detail("Version", data.latestVersion);
	} else if (m.type == MutationRef::ClearRange) {
		data.erase( m.param1, m.param2 );
		ASSERT( m.param2 > m.param1 );
		ASSERT( !data.isClearContaining( data.atLatest(), m.param1 ) );
		data.insert( m.param1, ValueOrClearToRef::clearTo(m.param2) );
		//TraceEvent(SevDebug, "ApplyMutationClearTo3")
		//	.detail("Key21", m.param1)
		//	.detail("Key22", m.param2)
		//	.detail("V2", data.latestVersion);
	}
}


template <class T>
void addMutation( T& target, Version version, MutationRef const& mutation ) {
	target.addMutation( version, mutation );
}

template <class T>
void addMutation( Reference<T>& target, Version version, MutationRef const& mutation ) {
	addMutation(*target, version, mutation);
}

template <class T>
void splitMutation(StorageCacheData* data, KeyRangeMap<T>& map, MutationRef const& m, Version ver) {
	if(isSingleKeyMutation((MutationRef::Type) m.type)) {
		auto i = map.rangeContaining(m.param1);
		if (i->value()) // If this key lies in the cached key-range on this server
			data->addMutation( i->range(), ver, m );
	}
	else if (m.type == MutationRef::ClearRange) {
		KeyRangeRef mKeys( m.param1, m.param2 );
		auto r = map.intersectingRanges( mKeys );
		for(auto i = r.begin(); i != r.end(); ++i) {
			if (i->value()) { // if this sub-range exists on this cache server
				KeyRangeRef k = mKeys & i->range();
				data->addMutation( i->range(), ver, MutationRef((MutationRef::Type)m.type, k.begin, k.end) );
			}
		}
	} else
		ASSERT(false);  // Unknown mutation type in splitMutations
}

void rollback( StorageCacheData* data, Version rollbackVersion, Version nextVersion ) {
	TEST(true); // call to cacheRange rollback
	// FIXME: enable when debugKeyRange is active
	//debugKeyRange("Rollback", rollbackVersion, allKeys);

	// FIXME: It's not straightforward to rollback certain versions from the VersionedMap.
	// It's doable. But for now, we choose to just throw away this cache role

	throw please_reboot();
}

void StorageCacheData::addMutation(KeyRangeRef const& cachedKeyRange, Version version, MutationRef const& mutation) {
	MutationRef expanded = mutation;
	auto& mLog = addVersionToMutationLog(version);

	if ( !expandMutation( expanded, data(), cachedKeyRange.end, mLog.arena()) ) {
		return;
	}
	expanded = addMutationToMutationLog(mLog, expanded);
	// FIXME: enable when debugMutation is active
	if (false && debugMutation("expandedMutation", version, expanded)) {
		const char* type =
			mutation.type == MutationRef::SetValue ? "SetValue" :
			mutation.type == MutationRef::ClearRange ? "ClearRange" :
			mutation.type == MutationRef::DebugKeyRange ? "DebugKeyRange" :
			mutation.type == MutationRef::DebugKey ? "DebugKey" :
			"UnknownMutation";
		printf("DEBUGMUTATION:\t%.6f\t%s\t%s\t%s\t%s\t%s\n",
			   now(), g_network->getLocalAddress().toString().c_str(), "originalMutation",
			   type, printable(mutation.param1).c_str(), printable(mutation.param2).c_str());
		printf("  Cached Key-range: %s - %s\n", printable(cachedKeyRange.begin).c_str(), printable(cachedKeyRange.end).c_str());
	}
	applyMutation( expanded, mLog.arena(), mutableData() );
	//printf("\nSCUpdate: Printing versioned tree after applying mutation\n");
	//mutableData().printTree(version);

}

void removeDataRange( StorageCacheData *sc, Standalone<VersionUpdateRef> &mLV, KeyRangeMap<Reference<CacheRangeInfo>>& cacheRanges, KeyRangeRef range ) {
	// modify the latest version of data to remove all sets and trim all clears to exclude range.
	// Add a clear to mLV (mutationLog[data.getLatestVersion()]) that ensures all keys in range are removed from the disk when this latest version becomes durable
	// mLV is also modified if necessary to ensure that split clears can be forgotten

	MutationRef clearRange( MutationRef::ClearRange, range.begin, range.end );
	clearRange = sc->addMutationToMutationLog( mLV, clearRange );

	auto& data = sc->mutableData();

	// Expand the range to the right to include other cacheRanges not in versionedData
	for( auto r = cacheRanges.rangeContaining(range.end); r != cacheRanges.ranges().end() && !r->value()->isInVersionedData(); ++r )
		range = KeyRangeRef(range.begin, r->end());

	auto endClear = data.atLatest().lastLess( range.end );
	if (endClear && endClear->isClearTo() && endClear->getEndKey() > range.end ) {
		// This clear has been bumped up to insertVersion==data.getLatestVersion and needs a corresponding mutation log entry to forget
		MutationRef m( MutationRef::ClearRange, range.end, endClear->getEndKey() );
		m = sc->addMutationToMutationLog( mLV, m );
		data.insert( m.param1, ValueOrClearToRef::clearTo( m.param2 ) );
	}

	auto beginClear = data.atLatest().lastLess( range.begin );
	if (beginClear && beginClear->isClearTo() && beginClear->getEndKey() > range.begin ) {
		// We don't need any special mutationLog entry - because the begin key and insert version are unchanged the original clear
		//   mutation works to forget this one - but we need range.begin in the right arena
		KeyRef rb(  mLV.arena(), range.begin );
		// insert() invalidates beginClear, so beginClear.key() is not safe to pass to it by reference
		data.insert( KeyRef(beginClear.key()), ValueOrClearToRef::clearTo( rb ), beginClear.insertVersion() );
	}

	data.erase( range.begin, range.end );
}

//void setAvailableStatus( StorageServer* self, KeyRangeRef keys, bool available );
//void setAssignedStatus( StorageServer* self, KeyRangeRef keys, bool nowAssigned );

void coalesceCacheRanges(StorageCacheData *data, KeyRangeRef keys) {
	auto cacheRanges = data->cachedRangeMap.intersectingRanges(keys);
	auto fullRange = data->cachedRangeMap.ranges();

	auto iter = cacheRanges.begin();
	if( iter != fullRange.begin() ) --iter;
	auto iterEnd = cacheRanges.end();
	if( iterEnd != fullRange.end() ) ++iterEnd;

	bool lastReadable = false;
	bool lastNotAssigned = false;
	KeyRangeMap<Reference<CacheRangeInfo>>::Iterator lastRange;

	for( ; iter != iterEnd; ++iter) {
		if( lastReadable && iter->value()->isReadable() ) {
			KeyRange range = KeyRangeRef( lastRange->begin(), iter->end() );
			data->addCacheRange( CacheRangeInfo::newReadWrite( range, data) );
			iter = data->cachedRangeMap.rangeContaining(range.begin);
		} else if( lastNotAssigned && iter->value()->notAssigned() ) {
			KeyRange range = KeyRangeRef( lastRange->begin(), iter->end() );
			data->addCacheRange( CacheRangeInfo::newNotAssigned( range) );
			iter = data->cachedRangeMap.rangeContaining(range.begin);
		}

		lastReadable = iter->value()->isReadable();
		lastNotAssigned = iter->value()->notAssigned();
		lastRange = iter;
	}
}

ACTOR Future<Standalone<RangeResultRef>> tryFetchRange( Database cx, Version version, KeyRangeRef keys, GetRangeLimits limits, bool* isTooOld ) {
	state Transaction tr( cx );
	state Standalone<RangeResultRef> output;
	state KeySelectorRef begin = firstGreaterOrEqual( keys.begin );
	state KeySelectorRef end = firstGreaterOrEqual( keys.end );

	if( *isTooOld )
		throw transaction_too_old();

	ASSERT(!cx->switchable);
	tr.setVersion( version );
	tr.info.taskID = TaskPriority::FetchKeys;
	limits.minRows = 0;

	try {
		loop {
			Standalone<RangeResultRef> rep = wait( tr.getRange( begin, end, limits, true ) );
			limits.decrement( rep );

			if( limits.isReached() || !rep.more ) {
				if( output.size() ) {
					output.arena().dependsOn( rep.arena() );
					output.append( output.arena(), rep.begin(), rep.size() );
					if( limits.isReached() && rep.readThrough.present() )
						output.readThrough = rep.readThrough.get();
				} else {
					output = rep;
				}

				output.more = limits.isReached();

				return output;
			} else if( rep.readThrough.present() ) {
				output.arena().dependsOn( rep.arena() );
				if( rep.size() ) {
					output.append( output.arena(), rep.begin(), rep.size() );
					ASSERT( rep.readThrough.get() > rep.end()[-1].key );
				} else {
					ASSERT( rep.readThrough.get() > keys.begin );
				}
				begin = firstGreaterOrEqual( rep.readThrough.get() );
			} else {
				output.arena().dependsOn( rep.arena() );
				output.append( output.arena(), rep.begin(), rep.size() );
				begin = firstGreaterThan( output.end()[-1].key );
			}
		}
	} catch( Error &e ) {
		if( begin.getKey() != keys.begin && ( e.code() == error_code_transaction_too_old || e.code() == error_code_future_version || e.code() == error_code_process_behind ) ) {
			if( e.code() == error_code_transaction_too_old )
				*isTooOld = true;
			output.more = true;
			if( begin.isFirstGreaterOrEqual() )
				output.readThrough = begin.getKey();
			return output;
		}
		throw;
	}
}

ACTOR Future<Void> fetchKeys( StorageCacheData *data, StorageCacheUpdater* updater, AddingCacheRange* cacheRange ) {
	state TraceInterval interval("SCFetchKeys");
	state KeyRange keys = cacheRange->keys;
	//state Future<Void> warningLogger = logFetchKeysWarning(cacheRange);
	state double startt = now();
	// TODO  we should probably change this for cache server
	state int fetchBlockBytes = BUGGIFY ? SERVER_KNOBS->BUGGIFY_BLOCK_BYTES : SERVER_KNOBS->FETCH_BLOCK_BYTES;

	// delay(0) to force a return to the run loop before the work of fetchKeys is started.
	//  This allows adding->start() to be called inline with CSK.
	wait( data->coreStarted.getFuture() && delay( 0 ) );

	try {
		// FIXME: enable when debugKeyRange is active
		//debugKeyRange("fetchKeysBegin", data->version.get(), cacheRange->keys);

		TraceEvent(SevDebug, interval.begin(), data->thisServerID)
			.detail("KeyBegin", cacheRange->keys.begin)
			.detail("KeyEnd",cacheRange->keys.end);

		validate(data);

		// TODO: double check the following block of code!!
		// We want to make sure that we can't query below lastAvailable, by waiting for the oldestVersion to become lastAvaialble
		auto navr = data->newestAvailableVersion.intersectingRanges( keys );
		Version lastAvailable = invalidVersion;
		for(auto r=navr.begin(); r!=navr.end(); ++r) {
			ASSERT( r->value() != latestVersion );
			lastAvailable = std::max(lastAvailable, r->value());
		}
		auto ndvr = data->newestDirtyVersion.intersectingRanges( keys );
		for(auto r=ndvr.begin(); r!=ndvr.end(); ++r)
			lastAvailable = std::max(lastAvailable, r->value());

		if (lastAvailable != invalidVersion && lastAvailable >= data->oldestVersion.get()) {
			TEST(true);
			wait( data->oldestVersion.whenAtLeast(lastAvailable+1) );
		}

		TraceEvent(SevDebug, "SCFetchKeysVersionSatisfied", data->thisServerID).detail("FKID", interval.pairID);

		wait( data->fetchKeysParallelismLock.take( TaskPriority::DefaultYield, fetchBlockBytes ) );
		state FlowLock::Releaser holdingFKPL( data->fetchKeysParallelismLock, fetchBlockBytes );

		//state double executeStart = now();
		//++data->counters.fetchWaitingCount;
		//data->counters.fetchWaitingMS += 1000*(executeStart - startt);

		// Fetch keys gets called while the update actor is processing mutations. data->version will not be updated until all mutations for a version
		// have been processed. We need to take the updateVersionLock to ensure data->version is greater than the version of the mutation which caused
		// the fetch to be initiated.
		wait( data->updateVersionLock.take() );

		cacheRange->phase = AddingCacheRange::Fetching;
		state Version fetchVersion = data->version.get();

		data->updateVersionLock.release();

		wait(delay(0));

		TraceEvent(SevDebug, "SCFetchKeysUnblocked", data->thisServerID).detail("FKID", interval.pairID).detail("Version", fetchVersion);

		// Get the history
		state int debug_getRangeRetries = 0;
		state int debug_nextRetryToLog = 1;
		state bool isTooOld = false;

		//FIXME: this should invalidate the location cache for cacheServers
		//data->cx->invalidateCache(keys);

		loop {
			try {
				TEST(true);		// Fetching keys for transferred cacheRange

				state Standalone<RangeResultRef> this_block = wait( tryFetchRange( data->cx, fetchVersion, keys, GetRangeLimits( CLIENT_KNOBS->ROW_LIMIT_UNLIMITED, fetchBlockBytes ), &isTooOld ) );

				state int expectedSize = (int)this_block.expectedSize() + (8-(int)sizeof(KeyValueRef))*this_block.size();

				TraceEvent(SevDebug, "SCFetchKeysBlock", data->thisServerID).detail("FKID", interval.pairID)
					.detail("BlockRows", this_block.size()).detail("BlockBytes", expectedSize)
					.detail("KeyBegin", keys.begin).detail("KeyEnd", keys.end)
					.detail("Last", this_block.size() ? this_block.end()[-1].key : std::string())
					.detail("Version", fetchVersion).detail("More", this_block.more);
				// FIXME: enable when debugKeyRange is active
				//debugKeyRange("fetchRange", fetchVersion, keys);

				// FIXME: enable when debugMutation is active
				//for(auto k = this_block.begin(); k != this_block.end(); ++k) debugMutation("fetch", fetchVersion, MutationRef(MutationRef::SetValue, k->key, k->value));

				data->counters.bytesFetched += expectedSize;
				if( fetchBlockBytes > expectedSize ) {
					holdingFKPL.release( fetchBlockBytes - expectedSize );
				}

				//Write this_block to mutationLog and versionedMap
				state KeyValueRef *kvItr = this_block.begin();
				for(; kvItr != this_block.end(); ++kvItr) {
					applyMutation(updater, data, MutationRef(MutationRef::SetValue, kvItr->key, kvItr->value), fetchVersion);
					data->counters.bytesFetched += expectedSize;
					wait(yield());
				}

				// TODO: If there was more to be fetched and we hit the limit before - possibly a case where data doesn't fit on this cache. For now, we can just fail this cache role.
				// In future, we should think about evicting some data to make room for the remaining keys
				if (this_block.more) {
					TraceEvent(SevDebug, "CacheWarmupMoreDataThanLimit", data->thisServerID);
					throw please_reboot();
				}

				this_block = Standalone<RangeResultRef>();

				if (BUGGIFY) wait( delay( 1 ) );

				break;
			} catch (Error& e) {
				TraceEvent("SCFKBlockFail", data->thisServerID).error(e,true).suppressFor(1.0).detail("FKID", interval.pairID);
				if (e.code() == error_code_transaction_too_old){
					TEST(true); // A storage server has forgotten the history data we are fetching
					Version lastFV = fetchVersion;
					fetchVersion = data->version.get();
					isTooOld = false;

					// Throw away deferred updates from before fetchVersion, since we don't need them to use blocks fetched at that version
					while (!cacheRange->updates.empty() && cacheRange->updates[0].version <= fetchVersion) cacheRange->updates.pop_front();

					// TODO: NEELAM: what's this for?
					//FIXME: remove when we no longer support upgrades from 5.X
					if(debug_getRangeRetries >= 100) {
						data->cx->enableLocalityLoadBalance = false;
					}

					debug_getRangeRetries++;
					if (debug_nextRetryToLog==debug_getRangeRetries){
						debug_nextRetryToLog += std::min(debug_nextRetryToLog, 1024);
						TraceEvent(SevWarn, "SCFetchPast", data->thisServerID).detail("TotalAttempts", debug_getRangeRetries).detail("FKID", interval.pairID).detail("V", lastFV).detail("N", fetchVersion).detail("E", data->version.get());
					}
				} else if (e.code() == error_code_future_version || e.code() == error_code_process_behind) {
					TEST(true); // fetchKeys got future_version or process_behind, so there must be a huge storage lag somewhere.  Keep trying.
				} else {
					throw;
				}
				wait( delayJittered( FLOW_KNOBS->PREVENT_FAST_SPIN_DELAY ) );
			}
		}

		// We have completed the fetch and write of the data, now we wait for MVCC window to pass.
		// As we have finished this work, we will allow more work to start...
		cacheRange->fetchComplete.send(Void());

		// TODO revisit the following block of code
		//TraceEvent(SevDebug, "SCFKBeforeFinalCommit", data->thisServerID).detail("FKID", interval.pairID).detail("SV", data->storageVersion()).detail("DV", data->durableVersion.get());
		// Directly commit()ing the IKVS would interfere with updateStorage, possibly resulting in an incomplete version being recovered.
		// Instead we wait for the updateStorage loop to commit something (and consequently also what we have written)

		// TODO: do we need this kind of wait? we are not going to make anything durable and hence no fear of wrong recovery
		//wait( data->durableVersion.whenAtLeast( data->storageVersion()+1 ) );
		holdingFKPL.release();

		//TraceEvent(SevDebug, "SCFKAfterFinalCommit", data->thisServerID).detail("FKID", interval.pairID).detail("SV", data->storageVersion()).detail("DV", data->durableVersion.get());

		// Wait to run during pullAsyncData, after a new batch of versions is received from the tlog
		Promise<FetchInjectionInfo*> p;
		data->readyFetchKeys.push_back( p );

		FetchInjectionInfo* batch = wait( p.getFuture() );
		TraceEvent(SevDebug, "SCFKUpdateBatch", data->thisServerID).detail("FKID", interval.pairID);

		cacheRange->phase = AddingCacheRange::Waiting;

		// Choose a transferredVersion.  This choice and timing ensure that
		//   * The transferredVersion can be mutated in versionedData
		//   * The transferredVersion isn't yet committed to storage (so we can write the availability status change)
		//   * The transferredVersion is <= the version of any of the updates in batch, and if there is an equal version
		//     its mutations haven't been processed yet
		cacheRange->transferredVersion = data->version.get() + 1;
		data->mutableData().createNewVersion( cacheRange->transferredVersion );
		ASSERT( cacheRange->transferredVersion > data->oldestVersion.get() );
		ASSERT( cacheRange->transferredVersion == data->data().getLatestVersion() );

		TraceEvent(SevDebug, "SCFetchKeysHaveData", data->thisServerID).detail("FKID", interval.pairID)
			.detail("Version", cacheRange->transferredVersion).detail("OldestVersion", data->oldestVersion.get());
		validate(data);

		// Put the updates that were collected during the FinalCommit phase into the batch at the transferredVersion.
		// The mutations will come back through AddingCacheRange::addMutations and be applied to versionedMap and mutationLog as normal.
		// The lie about their version is acceptable because this cacheRange will never be read at versions < transferredVersion
		for(auto i=cacheRange->updates.begin(); i!=cacheRange->updates.end(); ++i) {
			i->version = cacheRange->transferredVersion;
			batch->arena.dependsOn(i->arena());
		}

		int startSize = batch->changes.size();
		TEST(startSize); //Adding fetch data to a batch which already has changes
		batch->changes.resize( batch->changes.size()+cacheRange->updates.size() );

		//FIXME: pass the deque back rather than copy the data
		std::copy( cacheRange->updates.begin(), cacheRange->updates.end(), batch->changes.begin()+startSize );
		Version checkv = cacheRange->transferredVersion;

		for(auto b = batch->changes.begin()+startSize; b != batch->changes.end(); ++b ) {
			ASSERT( b->version >= checkv );
			checkv = b->version;
			// FIXME: enable when debugMutation is active
			//for(auto& m : b->mutations)
			//	debugMutation("fetchKeysFinalCommitInject", batch->changes[0].version, m);
		}

		cacheRange->updates.clear();

		// TODO: NEELAM: what exactly does it do? Writing some mutations to log. Do we need it for caches?
		//setAvailableStatus(data, keys, true); // keys will be available when getLatestVersion()==transferredVersion is durable

		// Wait for the transferredVersion (and therefore the cacheRange data) to be committed and compacted.
		// TODO: double check.
		wait( data->oldestVersion.whenAtLeast( cacheRange->transferredVersion ) );

		ASSERT( data->cachedRangeMap[cacheRange->keys.begin]->assigned() && data->cachedRangeMap[cacheRange->keys.begin]->keys == cacheRange->keys );  // We aren't changing whether the cacheRange is assigned
		data->newestAvailableVersion.insert(cacheRange->keys, latestVersion);
		cacheRange->readWrite.send(Void());
		data->addCacheRange( CacheRangeInfo::newReadWrite(cacheRange->keys, data) );   // invalidates cacheRange!
		coalesceCacheRanges(data, keys);

		validate(data);

		//++data->counters.fetchExecutingCount;
		//data->counters.fetchExecutingMS += 1000*(now() - executeStart);

		TraceEvent(SevDebug, interval.end(), data->thisServerID);
	} catch (Error &e){
		TraceEvent(SevDebug, interval.end(), data->thisServerID).error(e, true).detail("Version", data->version.get());

		// TODO define the shuttingDown state of cache server
		if (e.code() == error_code_actor_cancelled && /* !data->shuttingDown &&*/ cacheRange->phase >= AddingCacheRange::Fetching) {
			if (cacheRange->phase < AddingCacheRange::Waiting) {
				// TODO Not sure if it's okay to do this here!!
				removeDataRange( data, data->addVersionToMutationLog(data->data().getLatestVersion()), data->cachedRangeMap, keys );
				//data->storage.clearRange( keys );
			} else {
				ASSERT( data->data().getLatestVersion() > data->version.get() );
				removeDataRange( data, data->addVersionToMutationLog(data->data().getLatestVersion()), data->cachedRangeMap, keys );
				//setAvailableStatus(data, keys, false);
				// Prevent another, overlapping fetchKeys from entering the Fetching phase until data->data().getLatestVersion() is durable
				data->newestDirtyVersion.insert( keys, data->data().getLatestVersion() );
			}
		}

		TraceEvent(SevError, "SCFetchKeysError", data->thisServerID)
			.error(e)
			.detail("Elapsed", now()-startt)
			.detail("KeyBegin", keys.begin)
			.detail("KeyEnd",keys.end);
		if (e.code() != error_code_actor_cancelled)
			data->otherError.sendError(e);  // Kill the cache server.  Are there any recoverable errors?
		throw; // goes nowhere
	}

	return Void();
};

AddingCacheRange::AddingCacheRange( StorageCacheData* server, StorageCacheUpdater* updater, KeyRangeRef const& keys )
	: server(server), keys(keys), transferredVersion(invalidVersion), phase(WaitPrevious)
{
	fetchClient = fetchKeys(server, updater, this);
}

void AddingCacheRange::addMutation( Version version, MutationRef const& mutation ){
	if (mutation.type == mutation.ClearRange) {
		ASSERT( keys.begin<=mutation.param1 && mutation.param2<=keys.end );
	}
	else if (isSingleKeyMutation((MutationRef::Type) mutation.type)) {
		ASSERT( keys.contains(mutation.param1) );
	}

	if (phase == WaitPrevious) {
		// Updates can be discarded
	} else if (phase == Fetching) {
		if (!updates.size() || version > updates.end()[-1].version) {
			VerUpdateRef v;
			v.version = version;
			v.isPrivateData = false;
			updates.push_back(v);
		} else {
			ASSERT( version == updates.end()[-1].version );
		}
		updates.back().mutations.push_back_deep( updates.back().arena(), mutation );
	} else if (phase == Waiting) {
		server->addMutation(keys, version, mutation);
	} else ASSERT(false);
}

void CacheRangeInfo::addMutation(Version version, MutationRef const& mutation) {
	ASSERT( (void *)this);
	ASSERT( keys.contains( mutation.param1 ) );
	if (adding)
		adding->addMutation(version, mutation);
	else if (readWrite)
		readWrite->addMutation(this->keys, version, mutation);
	else if (mutation.type != MutationRef::ClearRange) { //TODO NEELAM: ClearRange mutations are ignored (why do we even allow them on un-assigned range?)
		TraceEvent(SevError, "DeliveredToNotAssigned").detail("Version", version).detail("Mutation", mutation.toString());
		ASSERT(false);  // Mutation delivered to notAssigned cacheRange!
	}
}

void cacheWarmup( StorageCacheData *data, StorageCacheUpdater* updater, const KeyRangeRef& keys, bool nowAssigned, Version version) {

	ASSERT( !keys.empty() );

	validate(data);

	// FIXME: enable when debugKeyRange is active
	//debugKeyRange( nowAssigned ? "KeysAssigned" : "KeysUnassigned", version, keys );

	bool isDifferent = false;
	auto existingCacheRanges = data->cachedRangeMap.intersectingRanges(keys);
	for( auto it = existingCacheRanges.begin(); it != existingCacheRanges.end(); ++it ) {
		if( nowAssigned != it->value()->assigned() ) {
			isDifferent = true;
			TraceEvent("SCWRangeDifferent", data->thisServerID)
			  .detail("KeyBegin", it->range().begin)
			  .detail("KeyEnd", it->range().end);
			break;
		}
	}
	if( !isDifferent ) {
		TraceEvent("SCWShortCircuit", data->thisServerID)
			.detail("KeyBegin", keys.begin)
			.detail("KeyEnd", keys.end);
		return;
	}

	// Save a backup of the CacheRangeInfo references before we start messing with cacheRanges, in order to defer fetchKeys cancellation (and
	// its potential call to removeDataRange()) until cacheRanges is again valid
	vector< Reference<CacheRangeInfo> > oldCacheRanges;
	auto ocr = data->cachedRangeMap.intersectingRanges(keys);
	for(auto r = ocr.begin(); r != ocr.end(); ++r)
		oldCacheRanges.push_back( r->value() );

	// As addCacheRange (called below)'s documentation requires, reinitialize any overlapping range(s)
	auto ranges = data->cachedRangeMap.getAffectedRangesAfterInsertion( keys, Reference<CacheRangeInfo>() );  // null reference indicates the range being changed
	for(int i=0; i<ranges.size(); i++) {
		if (!ranges[i].value) {
			ASSERT( (KeyRangeRef&)ranges[i] == keys ); // there shouldn't be any nulls except for the range being inserted
		} else if (ranges[i].value->notAssigned())
			data->addCacheRange( CacheRangeInfo::newNotAssigned(ranges[i]) );
		else if (ranges[i].value->isReadable())
			data->addCacheRange( CacheRangeInfo::newReadWrite(ranges[i], data) );
		else {
			ASSERT( ranges[i].value->adding );
			data->addCacheRange( CacheRangeInfo::newAdding( data, updater, ranges[i] ) );
			TEST( true );	// cacheWarmup reFetchKeys
		}
	}

	// CacheRange state depends on nowAssigned and whether the data is available (actually assigned in memory or on the disk) up to the given
	// version.  The latter depends on data->newestAvailableVersion, so loop over the ranges of that.
	// SOMEDAY: Could this just use cacheRanges?  Then we could explicitly do the removeDataRange here when an adding/transferred cacheRange is cancelled
	auto vr = data->newestAvailableVersion.intersectingRanges(keys);
	std::vector<std::pair<KeyRange,Version>> changeNewestAvailable;
	std::vector<KeyRange> removeRanges;
	for (auto r = vr.begin(); r != vr.end(); ++r) {
		KeyRangeRef range = keys & r->range();
		bool dataAvailable = r->value()==latestVersion || r->value() >= version;
		/*TraceEvent("CSKRange", data->thisServerID)
			.detail("KeyBegin", range.begin)
			.detail("KeyEnd", range.end)
			.detail("Available", dataAvailable)
			.detail("NowAssigned", nowAssigned)
			.detail("NewestAvailable", r->value())
			.detail("CacheRangeState0", data->cachedRangeMap[range.begin]->debugDescribeState());*/
		if (!nowAssigned) {
			if (dataAvailable) {
				ASSERT( r->value() == latestVersion);  // Not that we care, but this used to be checked instead of dataAvailable
				ASSERT( data->mutableData().getLatestVersion() > version);
				changeNewestAvailable.emplace_back(range, version);
				removeRanges.push_back( range );
			}
			data->addCacheRange( CacheRangeInfo::newNotAssigned(range) );
		} else if (!dataAvailable) {
			// SOMEDAY: Avoid restarting adding/transferred cacheRanges
			if (version==0){ // bypass fetchkeys; cacheRange is known empty at version 0
				changeNewestAvailable.emplace_back(range, latestVersion);
				data->addCacheRange( CacheRangeInfo::newReadWrite(range, data) );
				//setAvailableStatus(data, range, true);
			} else {
				auto& cacheRange = data->cachedRangeMap[range.begin];
				if( !cacheRange->assigned() || cacheRange->keys != range )
					data->addCacheRange( CacheRangeInfo::newAdding(data, updater, range) );
			}
		} else {
			changeNewestAvailable.emplace_back(range, latestVersion);
			data->addCacheRange( CacheRangeInfo::newReadWrite(range, data) );
		}
	}
	// Update newestAvailableVersion when a cacheRange becomes (un)available (in a separate loop to avoid invalidating vr above)
	for(auto r = changeNewestAvailable.begin(); r != changeNewestAvailable.end(); ++r)
		data->newestAvailableVersion.insert( r->first, r->second );

	// TODO
	//if (!nowAssigned)
	//	data->metrics.notifyNotReadable( keys );

	coalesceCacheRanges( data, KeyRangeRef(ranges[0].begin, ranges[ranges.size()-1].end) );

	// Now it is OK to do removeDataRanges, directly and through fetchKeys cancellation (and we have to do so before validate())
	oldCacheRanges.clear();
	ranges.clear();
	for(auto r=removeRanges.begin(); r!=removeRanges.end(); ++r) {
		removeDataRange( data, data->addVersionToMutationLog(data->data().getLatestVersion()), data->cachedRangeMap, *r );
		//setAvailableStatus(data, *r, false);
	}
	validate(data);
}

// Helper class for updating the storage cache (i.e. applying mutations)
class StorageCacheUpdater {
public:
	StorageCacheUpdater() : fromVersion(invalidVersion), currentVersion(invalidVersion), processedCacheStartKey(false) {}
	StorageCacheUpdater(Version currentVersion) : fromVersion(currentVersion), currentVersion(currentVersion), processedCacheStartKey(false) {}

	void applyMutation(StorageCacheData* data, MutationRef const& m , Version ver) {
		//TraceEvent("SCNewVersion", data->thisServerID).detail("VerWas", data->mutableData().latestVersion).detail("ChVer", ver);

		if(currentVersion != ver) {
			fromVersion = currentVersion;
			currentVersion = ver;
			data->mutableData().createNewVersion(ver);
		}

		if (m.param1.startsWith( systemKeys.end )) {
			TraceEvent("SCPrivateData", data->thisServerID).detail("Mutation", m.toString()).detail("Version", ver);
			applyPrivateCacheData( data, m );
		} else {
			// FIXME: enable when debugMutation is active
			//for(auto m = changes[c].mutations.begin(); m; ++m) {
			//	debugMutation("SCUpdateMutation", changes[c].version, *m);
			//}

			splitMutation(data, data->cachedRangeMap, m, ver);
		}

		//TODO
		if (data->otherError.getFuture().isReady()) data->otherError.getFuture().get();
	}

	Version currentVersion;
private:
	Version fromVersion;
	KeyRef cacheStartKey;
	bool nowAssigned;
	bool processedCacheStartKey;

	// Applies private mutations, as the name suggests. It basically establishes the key-ranges
	// that this cache server is responsible for
	// TODO Revisit during failure handling. Might we loose some private mutations?
	void applyPrivateCacheData( StorageCacheData* data, MutationRef const& m ) {
		TraceEvent(SevDebug, "SCPrivateCacheMutation", data->thisServerID).detail("Mutation", m.toString());

		if (processedCacheStartKey) {
			// we expect changes in pairs, [begin,end). This mutation is for end key of the range
			ASSERT (m.type == MutationRef::SetValue && m.param1.startsWith(data->ck));
			KeyRangeRef keys( cacheStartKey.removePrefix(data->ck), m.param1.removePrefix(data->ck));
			//setAssignedStatus( data, keys, nowAssigned );
			//data->cachedRangeMap.insert(keys, true);
			//fprintf(stderr, "SCPrivateCacheMutation: begin: %s, end: %s\n", printable(keys.begin).c_str(), printable(keys.end).c_str());

			// Warmup the cache for the newly added key-range
			cacheWarmup(data, this, keys, nowAssigned, currentVersion-1);
			processedCacheStartKey = false;
		} else if (m.type == MutationRef::SetValue && m.param1.startsWith( data->ck )) {
			// We expect changes in pairs, [begin,end), This mutation is for start key of the range
			cacheStartKey = m.param1;
			nowAssigned = m.param2 != serverKeysFalse;
			processedCacheStartKey = true;
		} else if (m.type == MutationRef::SetValue && m.param1 == lastEpochEndPrivateKey) {
			// lastEpochEnd transactions are guaranteed by the master to be alone in their own batch (version)
			// That means we don't have to worry about the impact on changeServerKeys

			Version rollbackVersion;
			BinaryReader br(m.param2, Unversioned());
			br >> rollbackVersion;

			if ( rollbackVersion < fromVersion && rollbackVersion > data->oldestVersion.get()) {
				TEST( true );  // CacheRangeApplyPrivateData cacheRange rollback
				TraceEvent(SevWarn, "Rollback", data->thisServerID)
					.detail("FromVersion", fromVersion)
					.detail("ToVersion", rollbackVersion)
					.detail("AtVersion", currentVersion)
					.detail("OldestVersion", data->oldestVersion.get());
				rollback( data, rollbackVersion, currentVersion );
			}
		} else {
			TraceEvent(SevWarn, "SCPrivateCacheMutation: Unknown private mutation");
			//ASSERT(false);  // Unknown private mutation
		}
	}
};

void applyMutation( StorageCacheUpdater* updater, StorageCacheData *data, MutationRef const& mutation, Version version ) {
	updater->applyMutation( data, mutation, version );
}


// Compacts the in-memory VersionedMap, i.e. removes versions below the desiredOldestVersion
// TODO revisit if we change the data structure of the VersionedMap
ACTOR Future<Void> compactCache(StorageCacheData* data) {
	loop {
		//TODO understand this, should we add delay here?
		//if (g_network->isSimulated()) {
		//	double endTime = g_simulator.checkDisabled(format("%s/compactCache", data->thisServerID.toString().c_str()));
		//	if(endTime > now()) {
		//		wait(delay(endTime - now(), TaskPriority::CompactCache));
		//	}
		//}

		// Wait until the desiredOldestVersion is greater than the current oldestVersion
		wait( data->desiredOldestVersion.whenAtLeast( data->oldestVersion.get()+1 ) );
		wait( delay(0, TaskPriority::CompactCache) );

		//TODO not really in use as of now. may need in some failure cases. Revisit and remove if no plausible use
		state Promise<Void> compactionInProgress;
		data->compactionInProgress = compactionInProgress.getFuture();
		//state Version oldestVersion = data->oldestVersion.get();
		state Version desiredVersion = data->desiredOldestVersion.get();
		// Call the compaction routine that does the actual work,
		//TraceEvent(SevDebug, "SCCompactCache", data->thisServerID).detail("DesiredVersion", desiredVersion);
		// TODO It's a synchronous function call as of now. Should it asynch?
		data->mutableData().compact(desiredVersion);
		Future<Void> finishedForgetting = data->mutableData().forgetVersionsBeforeAsync( desiredVersion,
																						 TaskPriority::CompactCache );
		data->oldestVersion.set( desiredVersion );
		wait( finishedForgetting );
		// TODO how do we yield here? This may not be enough, because compact() does the heavy lifting
		// of compating the VersionedMap. We should probably look into per version compaction and then
		// we can yield after compacting one version
		wait( yield(TaskPriority::CompactCache) );

		// TODO what flowlock to acquire during compaction?
		compactionInProgress.send(Void());
		wait(delay(2.0)); // we want to wait at least some small amount of time before
		//wait( delay(0, TaskPriority::CompactCache) ); //Setting compactionInProgess could cause the cache server to shut down, so delay to check for cancellation
	}
}

ACTOR Future<Void> pullAsyncData( StorageCacheData *data ) {
	state Future<Void> dbInfoChange = Void();
	state Reference<ILogSystem::IPeekCursor> cursor;
	state Version tagAt = 0;

	state StorageCacheUpdater updater(data->lastVersionWithData);
	state Version ver = invalidVersion;
	++data->counters.updateBatches;

	loop {
		loop {
			choose {
				when(wait( cursor ? cursor->getMore(TaskPriority::TLogCommit) : Never() ) ) {
					break;
				}
				when( wait( dbInfoChange ) ) {
					if( data->logSystem )
						cursor = data->logSystem->peekSingle( data->thisServerID, data->version.get() + 1, cacheTag, std::vector<std::pair<Version,Tag>>()) ;
					else
						cursor = Reference<ILogSystem::IPeekCursor>();
					dbInfoChange = data->db->onChange();
				}
			}
		}
		try {
			//TraceEvent("Versions", data->thisServerID).detail("CursorVersion", cursor->version().version).detail("PoppedVer", cursor->popped()).
			//	detail("CursorMaxKnownVersion", cursor->getMaxKnownVersion());

			// If the popped version is greater than our last version, we need to clear the cache
			if (cursor->version().version <= cursor->popped())
				throw please_reboot();

			data->lastTLogVersion = cursor->getMaxKnownVersion();
			data->versionLag = std::max<int64_t>(0, data->lastTLogVersion - data->version.get());

			state FetchInjectionInfo fii;
			state Reference<ILogSystem::IPeekCursor> cloneCursor2;
			loop{
				state uint64_t changeCounter = data->cacheRangeChangeCounter;
				bool epochEnd = false;
				bool hasPrivateData = false;
				bool firstMutation = true;
				bool dbgLastMessageWasProtocol = false;

				Reference<ILogSystem::IPeekCursor> cloneCursor1 = cursor->cloneNoMore();
				cloneCursor2 = cursor->cloneNoMore();

				//TODO cache servers should write the LogProtocolMessage when they are created
				//cloneCursor1->setProtocolVersion(data->logProtocol);
				cloneCursor1->setProtocolVersion(currentProtocolVersion);

				for (; cloneCursor1->hasMessage(); cloneCursor1->nextMessage()) {
					ArenaReader& cloneReader = *cloneCursor1->reader();

					if (LogProtocolMessage::isNextIn(cloneReader)) {
						LogProtocolMessage lpm;
						cloneReader >> lpm;
						dbgLastMessageWasProtocol = true;
						cloneCursor1->setProtocolVersion(cloneReader.protocolVersion());
						//TraceEvent(SevDebug, "SCReadingLPM", data->thisServerID).detail("Mutation", lpm.toString());
					}
					else {
						MutationRef msg;
						cloneReader >> msg;
						//TraceEvent(SevDebug, "SCReadingLog", data->thisServerID).detail("Mutation", msg.toString());

						if (firstMutation && msg.param1.startsWith(systemKeys.end))
							hasPrivateData = true;
						firstMutation = false;

						if (msg.param1 == lastEpochEndPrivateKey) {
							epochEnd = true;
							//ASSERT(firstMutation);
							ASSERT(dbgLastMessageWasProtocol);
						}

						dbgLastMessageWasProtocol = false;
					}
				}

				// Any fetchKeys which are ready to transition their cacheRanges to the adding,transferred state do so now.
				// If there is an epoch end we skip this step, to increase testability and to prevent inserting a version in the middle of a rolled back version range.
				while(!hasPrivateData && !epochEnd && !data->readyFetchKeys.empty()) {
					auto fk = data->readyFetchKeys.back();
					data->readyFetchKeys.pop_back();
					fk.send( &fii );
				}
				if (data->cacheRangeChangeCounter == changeCounter) break;
				//TEST(true); // A fetchKeys completed while we were doing this, so eager might be outdated.  Read it again.
			}

			data->debug_inApplyUpdate = true;
			if (EXPENSIVE_VALIDATION) data->data().atLatest().validate();
			validate(data);

			state bool injectedChanges = false;
			state int changeNum = 0;
			state int mutationBytes = 0;
			for(; changeNum < fii.changes.size(); changeNum++) {
				state int mutationNum = 0;
				state VerUpdateRef* pUpdate = &fii.changes[changeNum];
				for(; mutationNum < pUpdate->mutations.size(); mutationNum++) {
					TraceEvent("InjectedChanges", data->thisServerID).detail("Version", pUpdate->version);
					applyMutation(&updater, data, pUpdate->mutations[mutationNum], pUpdate->version);
					mutationBytes += pUpdate->mutations[mutationNum].totalSize();
					injectedChanges = true;
					if(false && mutationBytes > SERVER_KNOBS->DESIRED_UPDATE_BYTES) {
						mutationBytes = 0;
						wait(delay(SERVER_KNOBS->UPDATE_DELAY));
					}
				}
			}

			//FIXME: ensure this can only read data from the current version
			//cloneCursor2->setProtocolVersion(data->logProtocol);
			cloneCursor2->setProtocolVersion(currentProtocolVersion);
			ver = invalidVersion;

			// Now process the mutations
			for (; cloneCursor2->hasMessage(); cloneCursor2->nextMessage()) {
				ArenaReader& reader = *cloneCursor2->reader();

				//TraceEvent("Versions", data->thisServerID).detail("CursorVersion", cloneCursor2->version().version).detail("Ver", ver).detail("DataVersion", data->version.get()).detail("TLogVersion", data->lastTLogVersion);
				if (cloneCursor2->version().version > ver && cloneCursor2->version().version > data->version.get()) {
					++data->counters.updateVersions;
					ver = cloneCursor2->version().version;
				}
				if (LogProtocolMessage::isNextIn(reader)) {
					LogProtocolMessage lpm;
					reader >> lpm;

					// TODO should we store the logProtocol?
					data->logProtocol = reader.protocolVersion();
					cloneCursor2->setProtocolVersion(data->logProtocol);
					//TraceEvent(SevDebug, "SCReadingLPM", data->thisServerID).detail("Mutation", lpm.toString()).detail("LogProtocolVersion", data->logProtocol.version());
				}
				else {
					MutationRef msg;
					reader >> msg;
					//fprintf(stderr, "%lld : %s\n", cursor->version().version, msg.toString().c_str());

					if (ver != invalidVersion) // This change belongs to a version < minVersion
					{
						applyMutation(&updater, data, msg, ver);
						data->counters.mutationBytes += msg.totalSize();
						++data->counters.mutations;

						switch(msg.type) {
							case MutationRef::SetValue:
								++data->counters.setMutations;
								break;
							case MutationRef::ClearRange:
								++data->counters.clearRangeMutations;
								break;
							case MutationRef::AddValue:
							case MutationRef::And:
							case MutationRef::AndV2:
							case MutationRef::AppendIfFits:
							case MutationRef::ByteMax:
							case MutationRef::ByteMin:
							case MutationRef::Max:
							case MutationRef::Min:
							case MutationRef::MinV2:
							case MutationRef::Or:
							case MutationRef::Xor:
							case MutationRef::CompareAndClear:
								++data->counters.atomicMutations;
								break;
						}
					}
					else
						TraceEvent(SevError, "DiscardingPeekedData", data->thisServerID).detail("Mutation", msg.toString()).detail("Version", cursor->version().toString());

					tagAt = cursor->version().version + 1;
				}
			}

			if(ver != invalidVersion) {
				data->lastVersionWithData = ver;
			} else {
				ver = cloneCursor2->version().version - 1;
			}
			if(injectedChanges) data->lastVersionWithData = ver;

			data->debug_inApplyUpdate = false;

			if(ver != invalidVersion && ver > data->version.get()) {
				// FIXME: enable when debugKeyRange is active
				//debugKeyRange("SCUpdate", ver, allKeys);

				data->mutableData().createNewVersion(ver);

				// TODO what about otherError
				if (data->otherError.getFuture().isReady()) data->otherError.getFuture().get();

				// TODO may enable these later
				//data->noRecentUpdates.set(false);
				//data->lastUpdate = now();
				data->version.set( ver );		// Triggers replies to waiting gets for new version(s)
				// TODO double check
				//setDataVersion(data->thisServerID, data->version.get());

				// TODO what about otherError
				if (data->otherError.getFuture().isReady()) data->otherError.getFuture().get();

				// we can get rid of versions beyond maxVerionsInMemory at any point. Update the
				//desiredOldestVersion and that may invoke the compaction actor
				Version maxVersionsInMemory = SERVER_KNOBS->MAX_READ_TRANSACTION_LIFE_VERSIONS;
				Version proposedOldestVersion = data->version.get() - maxVersionsInMemory;
				proposedOldestVersion = std::max(proposedOldestVersion, data->oldestVersion.get());
				data->desiredOldestVersion.set(proposedOldestVersion);
			}

			validate(data);

			//TraceEvent("SCUpdatedVersions", data->thisServerID).detail("DataVersion", data->version.get()).detail("Version", ver);
			data->lastTLogVersion = cloneCursor2->getMaxKnownVersion();
			//TraceEvent("CursorVersions", data->thisServerID).detail("CursorVersion", cursor->version().version).detail("CloneCurserVersion", cloneCursor2->version().version).detail("TLogVersion", data->lastTLogVersion);
			cursor->advanceTo( cloneCursor2->version() );
			data->versionLag = std::max<int64_t>(0, data->lastTLogVersion - data->version.get());
			if(cursor->version().version >= data->lastTLogVersion) {
				if(data->behind) {
					TraceEvent("StorageCacheNoLongerBehind", data->thisServerID).detail("CursorVersion", cursor->version().version).detail("TLogVersion", data->lastTLogVersion);
				}
				data->behind = false;
			}
		} catch (Error& err) {
			state Error e = err;
			TraceEvent(SevDebug, "SCUpdateError", data->thisServerID).error(e).backtrace();
			if (e.code() == error_code_worker_removed) {
				throw please_reboot();
			} else {
				throw e;
			}
		}

		tagAt = std::max( tagAt, cursor->version().version);
	}
}

ACTOR Future<Void> watchInterface(StorageCacheData* self, StorageServerInterface ssi) {
	state Transaction tr(self->cx);
	state Key storageKey = storageCacheServerKey(ssi.id());
	loop {
		loop {
			tr.setOption(FDBTransactionOptions::LOCK_AWARE);
			tr.setOption(FDBTransactionOptions::ACCESS_SYSTEM_KEYS);
			try {
				Optional<Value> val = wait(tr.get(storageKey));
				// This could race with the data distributor trying to remove
				// the interface - but this is ok, as we don't need to kill
				// ourselves if FailureMonitor marks us as down (this might save
				// from unnecessary cache refreshes).
				if (!val.present()) {
					tr.set(storageKey, storageCacheServerValue(ssi));
					wait(tr.commit());
				}
				break;
			} catch (Error& e) {
				wait(tr.onError(e));
			}
		}
		wait(delay(5.0));
	}
}

ACTOR Future<Void> storageCacheServer(StorageServerInterface ssi, uint16_t id, Reference<AsyncVar<ServerDBInfo>> db) {
	state StorageCacheData self(ssi.id(), id, db);
	state ActorCollection actors(false);
	state Future<Void> dbInfoChange = Void();

	//TraceEvent("StorageCache_CacheServerInterface", self.thisServerID).detail("UID", ssi.uniqueID).detail("IsCacheServer", ssi.isCacheServer);
	// This helps identify the private mutations meant for this cache server
	self.ck = cacheKeysPrefixFor( id ).withPrefix(systemKeys.begin);  // FFFF/02cacheKeys/[this server]/

	actors.add(waitFailureServer(ssi.waitFailure.getFuture()));
	actors.add(traceCounters("CacheMetrics", self.thisServerID, SERVER_KNOBS->STORAGE_LOGGING_DELAY, &self.counters.cc, self.thisServerID.toString() + "/CacheMetrics"));

	// compactCache actor will periodically compact the cache when certain version condition is met
	actors.add(compactCache(&self));

	// pullAsyncData actor pulls mutations from the TLog and also applies them.
	actors.add(pullAsyncData(&self));
	actors.add(watchInterface(&self, ssi));

	self.coreStarted.send( Void() );

	loop {
		++self.counters.loops;
		choose {
		when( wait( dbInfoChange ) ) {
			dbInfoChange = db->onChange();
			//self.logSystem->set(ILogSystem::fromServerDBInfo( ssi.id(), db->get(), true ));
			self.logSystem = ILogSystem::fromServerDBInfo( self.thisServerID, self.db->get() );
		}
		when( GetValueRequest req = waitNext(ssi.getValue.getFuture()) ) {
			// TODO do we need to add throttling for cache servers? Probably not
			//actors.add(self->readGuard(req , getValueQ));
			actors.add(getValueQ(&self, req));
		}
		when( WatchValueRequest req = waitNext(ssi.watchValue.getFuture()) ) {
			ASSERT(false);
		}
		when (GetKeyRequest req = waitNext(ssi.getKey.getFuture())) {
			actors.add(getKey(&self, req));
		}
		when (GetKeyValuesRequest req = waitNext(ssi.getKeyValues.getFuture()) ) {
			actors.add(getKeyValues(&self, req));
		}
		when (GetShardStateRequest req = waitNext(ssi.getShardState.getFuture()) ) {
			ASSERT(false);
		}
		when (StorageQueuingMetricsRequest req = waitNext(ssi.getQueuingMetrics.getFuture())) {
			ASSERT(false);
		}
		//when( ReplyPromise<Version> reply = waitNext(ssi.getVersion.getFuture()) ) {
		//	ASSERT(false);
		//}
		when( ReplyPromise<KeyValueStoreType> reply = waitNext(ssi.getKeyValueStoreType.getFuture()) ) {
			ASSERT(false);
		}
		when(wait(actors.getResult())) {}
		}
	}
}