foundationdb/fdbserver/KeyValueStoreSQLite.actor.cpp

/*
 * KeyValueStoreSQLite.actor.cpp
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2018 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.
 */


#define SQLITE_THREADSAFE 0  // also in sqlite3.amalgamation.c!
#include "fdbrpc/crc32c.h"
#include "fdbserver/IKeyValueStore.h"
#include "fdbserver/CoroFlow.h"
#include "fdbserver/Knobs.h"
#include "flow/Hash3.h"

extern "C" {
#include "fdbserver/sqlite/sqliteInt.h"
u32 sqlite3VdbeSerialGet(const unsigned char*, u32, Mem*);
}
#include "flow/ThreadPrimitives.h"
#include "fdbserver/template_fdb.h"
#include "fdbrpc/simulator.h"
#include "flow/actorcompiler.h"  // This must be the last #include.

#if SQLITE_THREADSAFE == 0
	#define sqlite3_mutex_enter(x)
	#define sqlite3_mutex_leave(x)
#endif

void hexdump(FILE *fout, StringRef val);

/*#undef state
#include <Windows.h>*/

/*uint64_t getFileSize( const char* filename ) {
	HANDLE f = CreateFile( filename, GENERIC_READ, FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE, NULL, OPEN_EXISTING, 0, NULL);
	if (f == INVALID_HANDLE_VALUE) return 0;
	DWORD hi,lo;
	lo = GetFileSize(f, &hi);
	CloseHandle(f);
	return (uint64_t(hi)<<32) + lo;
}*/

struct SpringCleaningStats {
	int64_t springCleaningCount;
	int64_t lazyDeletePages;
	int64_t vacuumedPages;
	double springCleaningTime;
	double vacuumTime;
	double lazyDeleteTime;

	SpringCleaningStats() : springCleaningCount(0), lazyDeletePages(0), vacuumedPages(0), springCleaningTime(0.0), vacuumTime(0.0), lazyDeleteTime(0.0) {}
};

struct PageChecksumCodec {
	PageChecksumCodec(std::string const &filename) : pageSize(0), reserveSize(0), filename(filename), silent(false) {}

	int pageSize;
	int reserveSize;
	std::string filename;
	bool silent;

	struct SumType {
		bool operator==(const SumType &rhs) const { return part1 == rhs.part1 && part2 == rhs.part2; }
		uint32_t part1;
		uint32_t part2;
		std::string toString() { return format("0x%08x%08x", part1, part2); }
	};

	// Calculates and then either stores or verifies a checksum.
	// The checksum is read/stored at the end of the page buffer.
	// Page size is passed in as pageLen because this->pageSize is not always appropriate.
	// If write is true then the checksum is written into the page and true is returned.
	// If write is false then the checksum is compared to the in-page sum and the return value
	// is whether or not the checksums were equal.
	bool checksum(Pgno pageNumber, void *data, int pageLen, bool write) {
		ASSERT(pageLen > sizeof(SumType));

		char *pData = (char *)data;
		int dataLen = pageLen - sizeof(SumType);
		SumType *pSumInPage = (SumType *)(pData + dataLen);

		if (write) {
			// Always write a CRC32 checksum for new pages
			pSumInPage->part1 = 0; // Indicates CRC32 is being used
			pSumInPage->part2 = crc32c_append(0xfdbeefdb, static_cast<uint8_t*>(data), dataLen);
			return true;
		}

		SumType sum;
		if (pSumInPage->part1 == 0) {
			// part1 being 0 indicates with high probability that a CRC32 checksum
			// was used, so check that first. If this checksum fails, there is still
			// some chance the page was written with hashlittle2, so fall back to checking
			// hashlittle2
			sum.part1 = 0;
			sum.part2 = crc32c_append(0xfdbeefdb, static_cast<uint8_t*>(data), dataLen);
			if (sum == *pSumInPage) return true;
		}

		SumType hashLittle2Sum;
		hashLittle2Sum.part1 = pageNumber; // DO NOT CHANGE
		hashLittle2Sum.part2 = 0x5ca1ab1e;
		hashlittle2(pData, dataLen, &hashLittle2Sum.part1, &hashLittle2Sum.part2);
		if (hashLittle2Sum == *pSumInPage) return true;

		if (!silent) {
			TraceEvent trEvent(SevError, "SQLitePageChecksumFailure");
			trEvent.error(checksum_failed())
			    .detail("CodecPageSize", pageSize)
			    .detail("CodecReserveSize", reserveSize)
			    .detail("Filename", filename)
			    .detail("PageNumber", pageNumber)
			    .detail("PageSize", pageLen)
			    .detail("ChecksumInPage", pSumInPage->toString())
			    .detail("ChecksumCalculatedHL2", hashLittle2Sum.toString());
			if (pSumInPage->part1 == 0) trEvent.detail("ChecksumCalculatedCRC", sum.toString());
		}
		return false;
	}

	static void * codec(void *vpSelf, void *data, Pgno pageNumber, int op) {
		PageChecksumCodec *self = (PageChecksumCodec *)vpSelf;

		// Page write operations are 6 for DB page and 7 for journal page
		bool write = (op == 6 || op == 7);
		// Page read is operation 3, which must be the operation if it's not a write.
		ASSERT(write || op == 3);

		// Page 1 is special.  It contains the database configuration including Page Size and Reserve Size.
		// SQLite can't get authoritative values for these things until the Pager Codec has validated (and
		// potentially decrypted) Page 1 itself, so it can't tell the Pager Codec what those things are before
		// Page 1 is handled.  It will guess a Page Size of SQLITE_DEFAULT_PAGE_SIZE, and a Reserve Size based
		// on the pre-verified (and perhaps still encrypted) header in the Page 1 data that it will then pass
		// to the Pager Codec.
		//
		// So, Page 1 must be written and verifiable as a SQLITE_DEFAULT_PAGE_SIZE sized page as well as
		// the actual configured page size for the database, if it is larger.  A configured page size lower
		// than the default (in other words 512) results in undefined behavior.
		if(pageNumber == 1) {
			if(write && self->pageSize > SQLITE_DEFAULT_PAGE_SIZE) {
				self->checksum(pageNumber, data, SQLITE_DEFAULT_PAGE_SIZE, write);
			}
		}
		else {
			// For Page Numbers other than 1, reserve size must be the size of the checksum.
			if(self->reserveSize != sizeof(SumType)) {
				if(!self->silent)
					TraceEvent(SevWarnAlways, "SQLitePageChecksumFailureBadReserveSize")
						.detail("CodecPageSize", self->pageSize)
						.detail("CodecReserveSize", self->reserveSize)
						.detail("Filename", self->filename)
						.detail("PageNumber", pageNumber);

				return NULL;
			}
		}

		if(!self->checksum(pageNumber, data, self->pageSize, write))
			return NULL;

		return data;
	}

	static void sizeChange(void *vpSelf, int new_pageSize, int new_reserveSize) {
		PageChecksumCodec *self = (PageChecksumCodec *)vpSelf;
		self->pageSize = new_pageSize;
		self->reserveSize = new_reserveSize;
	}

	static void free(void *vpSelf) {
		PageChecksumCodec *self = (PageChecksumCodec *)vpSelf;
		delete self;
	}
};

struct SQLiteDB : NonCopyable {
	std::string filename;
	sqlite3* db;
	Btree* btree;
	int table, freetable;
	bool haveMutex;
	Reference<IAsyncFile> dbFile, walFile;
	bool page_checksums;
	bool fragment_values;
	PageChecksumCodec *pPagerCodec;  // we do NOT own this pointer, db does.

	void beginTransaction(bool write) {
		checkError("BtreeBeginTrans", sqlite3BtreeBeginTrans(btree, write));
	}
	void endTransaction() {
		checkError("BtreeCommit", sqlite3BtreeCommit(btree));
	}
	void rollback() {
		checkError("BtreeRollback", sqlite3BtreeRollback(btree));
	}

	void open(bool writable);
	void createFromScratch();

	SQLiteDB( std::string filename, bool page_checksums, bool fragment_values): filename(filename), db(NULL), btree(NULL), table(-1), freetable(-1), haveMutex(false), page_checksums(page_checksums), fragment_values(fragment_values) {}

	~SQLiteDB() {
		if (db) {
			if (haveMutex) {
				sqlite3_mutex_leave(db->mutex);
			}
			sqlite3_close( db );
		}
	}

	void initPagerCodec() {
		if(page_checksums) {
			int r = sqlite3_test_control(SQLITE_TESTCTRL_RESERVE, db, sizeof(PageChecksumCodec::SumType));
			if(r != 0) {
				TraceEvent(SevError, "BtreePageReserveSizeSetError").detail("Filename", filename).detail("ErrorCode", r);
				ASSERT(false);
			}
			// Always start with a new pager codec with default options.
			pPagerCodec = new PageChecksumCodec(filename);
			sqlite3BtreePagerSetCodec(btree, PageChecksumCodec::codec, PageChecksumCodec::sizeChange, PageChecksumCodec::free, pPagerCodec);
		}
	}

	void checkError( const char* context, int rc ) {
		//if (deterministicRandom()->random01() < .001) rc = SQLITE_INTERRUPT;
		if (rc) {
			// Our exceptions don't propagate through sqlite, so we don't know for sure if the error that caused this was
			// an injected fault.  Assume that if fault injection is happening, this is an injected fault.
			Error err = io_error();
			if (g_network->isSimulated() && (g_simulator.getCurrentProcess()->fault_injection_p1 || g_simulator.getCurrentProcess()->machine->machineProcess->fault_injection_p1 || g_simulator.getCurrentProcess()->rebooting))
				err = err.asInjectedFault();

			if (db)
				db->errCode = rc;
			if (rc == SQLITE_NOMEM) platform::outOfMemory(); // SOMEDAY: Trap out of memory errors at allocation time; check out different allocation options in sqlite

			TraceEvent(SevError, "DiskError").error(err).detail("In", context).detail("File", filename).detail("SQLiteError", sqlite3ErrStr(rc)).detail("SQLiteErrorCode", rc).GetLastError();
			throw err;
		}
	}
	void checkpoint( bool restart ) {
		int logSize=0, checkpointCount=0;
		//double t = timer();
		while (true) {
			int rc = sqlite3_wal_checkpoint_v2(db, 0, restart ? SQLITE_CHECKPOINT_RESTART : SQLITE_CHECKPOINT_FULL, &logSize, &checkpointCount);
			if (!rc) break;
			if ((sqlite3_errcode(db)&0xff) == SQLITE_BUSY) {
				//printf("#");
				//threadSleep(.010);
				sqlite3_sleep(10);
			} else
				checkError("checkpoint", rc);
		}
		//printf("Checkpoint (%0.1f ms): %d frames in log, %d checkpointed\n", (timer()-t)*1000, logSize, checkpointCount);
	}
	uint32_t freePages() {
		u32 fp = 0;
		sqlite3BtreeGetMeta(btree, BTREE_FREE_PAGE_COUNT, &fp);
		return fp;
	}
	bool vacuum() {  // Returns true if vacuum is complete or stalled by a lazy free root
		int rc = sqlite3BtreeIncrVacuum(btree);
		if (rc && rc != SQLITE_DONE) checkError("vacuum", rc);
		return rc == SQLITE_DONE;
	}
	int check(bool verbose) {
		int errors = 0;
		int tables[] = {1, table, freetable};
		TraceEvent("BTreeIntegrityCheckBegin").detail("Filename", filename);
		char* e = sqlite3BtreeIntegrityCheck(btree, tables, 3, 1000, &errors, verbose);
		if (!(g_network->isSimulated() && (g_simulator.getCurrentProcess()->fault_injection_p1 || g_simulator.getCurrentProcess()->rebooting))) {
			TraceEvent((errors||e) ? SevError : SevInfo, "BTreeIntegrityCheckResults").detail("Filename", filename).detail("ErrorTotal", errors);
			if(e != nullptr) {
				// e is a string containing 1 or more lines.  Create a separate trace event for each line.
				char *lineStart = e;
				while(lineStart != nullptr) {
					char *lineEnd = strstr(lineStart, "\n");
					if(lineEnd != nullptr) {
						*lineEnd = '\0';
						++lineEnd;
					}

					// If the line length found is not zero then print a trace event
					if(*lineStart != '\0')
						TraceEvent(SevError, "BTreeIntegrityCheck").detail("Filename", filename).detail("ErrorDetail", lineStart);
					lineStart = lineEnd;
				}
			}
			TEST(true);  // BTree integrity checked
		}
		if (e) sqlite3_free(e);

		return errors;
	}
	int checkAllPageChecksums();
};

class Statement : NonCopyable {
	SQLiteDB& db;
	sqlite3_stmt *stmt;

public:
	Statement( SQLiteDB& db, const char* sql )
		: db(db), stmt(NULL)
	{
		db.checkError("prepare", sqlite3_prepare_v2( db.db, sql, -1, &stmt, NULL));
	}
	~Statement() {
		try {
			db.checkError("finalize", sqlite3_finalize( stmt ));
		} catch (...) {
		}
	}
	Statement& reset() {
		db.checkError("reset", sqlite3_reset(stmt));
		return *this;
	}
	Statement& param(int i, StringRef value) {
		db.checkError("bind", sqlite3_bind_blob( stmt, i, value.begin(), value.size(), SQLITE_STATIC ));
		return *this;
	}
	Statement& param(int i, int value) {
		db.checkError("bind", sqlite3_bind_int( stmt, i, value ));
		return *this;
	}
	Statement& execute() {
		int r = sqlite3_step( stmt );
		if (r == SQLITE_ROW) db.checkError("execute called on statement that returns rows", r);
		if (r != SQLITE_DONE) db.checkError("execute", r);
		return *this;
	}
	bool nextRow() {
		int r = sqlite3_step( stmt );
		if (r == SQLITE_ROW) return true;
		if (r == SQLITE_DONE) return false;
		db.checkError( "nextRow", r );
		__assume(false); // NOT REACHED
	}
	StringRef column( int i ) {
		return StringRef(
			(const uint8_t*)sqlite3_column_blob(stmt, i),
			sqlite3_column_bytes(stmt, i) );
	}
};

void hexdump(FILE *fout, StringRef val) {
	int buflen = val.size();
	const unsigned char *buf = val.begin();
	int i, j;
	for (i=0; i<buflen; i+=32) {
		fprintf(fout, "%06x: ", i);
		for (j=0; j<32; j++) {
			if(j == 16)
				fprintf(fout, "  ");
			if (i+j < buflen)
				fprintf(fout, "%02x ", buf[i+j]);
			else
				fprintf(fout, "   ");
		}
		fprintf(fout, " ");
		for (j=0; j<32; j++) {
			if(j == 16)
				fprintf(fout, "  ");
			if (i+j < buflen)
				fprintf(fout, "%c", isprint(buf[i+j]) ? buf[i+j] : '.');
		}
		fprintf(fout, "\n");
	}
}

Value encode( KeyValueRef kv ) {
	int keyCode = kv.key.size()*2 + 12;
	int valCode = kv.value.size()*2 + 12;
	int header_size = sqlite3VarintLen(keyCode) + sqlite3VarintLen(valCode);
	int hh = sqlite3VarintLen(header_size);
	header_size += hh;
	if (hh < sqlite3VarintLen(header_size))
		header_size++;
	int size = header_size + kv.key.size() + kv.value.size();

	Value v;
	uint8_t* d = new (v.arena()) uint8_t[size];
	((ValueRef&)v) = KeyRef(d, size);
	d += sqlite3PutVarint( d, header_size );
	d += sqlite3PutVarint( d, keyCode );
	d += sqlite3PutVarint( d, valCode );
	memcpy(d, kv.key.begin(), kv.key.size());
	d += kv.key.size();
	memcpy(d, kv.value.begin(), kv.value.size());
	d += kv.value.size();
	ASSERT( d == v.begin()+size );
	return v;
}

// Fragments are encoded as (key, index, value) tuples
// An index of 0 indicates an unfragmented KV pair.
// For fragmented KV pairs, the values will be concatenated in index order.
//
// In the current implementation, index values are chosen to enable a single linear
// pass over the fragments, in forward or backward order, to immediately know the final
// unfragmented value size accurately enough to allocate a buffer that is certainly large
// enough to hold the defragmented bytes.
//
// However, the decoder could be made to work if these index value 'hints' become inaccurate
// due to a change in splitting logic or index numbering.  The decoder would just have to support
// buffer expansion as needed.
//
// Note that changing the following value constitutes a change in index numbering.
#define KV_FRAGMENT_INDEX_SIZE_HINT_FACTOR 4
Value encodeKVFragment( KeyValueRef kv, uint32_t index) {
	int keyCode = kv.key.size()*2 + 12;
	int valCode = kv.value.size()*2 + 12;
	// The SQLite type code for the index is the minimal number of bytes needed to store
	// a signed representation of the index value.  The type code for 0 is 0 (which is
	// actually the null type in SQLite).
	int8_t indexCode = 0;
	if (index != 0) {
		uint32_t tmp = index;
		while (tmp != 0) {
			++indexCode;
			tmp >>= 8;
		}
		// An increment is required if the high bit of the N-byte index value is set, since it is
		// positive number but SQLite only stores signed values and would interpret it as negative.
		if (index >> (8 * indexCode - 1)) ++indexCode;
	}

	int header_size = sqlite3VarintLen(keyCode) + sizeof(indexCode) + sqlite3VarintLen(valCode);
	int hh = sqlite3VarintLen(header_size);
	header_size += hh;
	if (hh < sqlite3VarintLen(header_size))
		header_size++;
	int size = header_size + kv.key.size() + indexCode + kv.value.size();

	Value v;
	uint8_t* d = new (v.arena()) uint8_t[size];
	((ValueRef&)v) = KeyRef(d, size);
	d += sqlite3PutVarint( d, header_size );
	d += sqlite3PutVarint( d, keyCode );
	*d++ = indexCode;
	d += sqlite3PutVarint( d, valCode );

	// Write key
	memcpy(d, kv.key.begin(), kv.key.size());
	d += kv.key.size();

	// Write index bytes, if any
	for(int i = indexCode - 1; i >= 0; --i) {
		d[i] = (uint8_t)index;
		index >>= 8;
	}
	d += indexCode;

	// Write value
	memcpy(d, kv.value.begin(), kv.value.size());
	d += kv.value.size();
	ASSERT( d == v.begin()+size );
	return v;
}

int getEncodedSize( int keySize, int valuePrefixSize ) {
	int keyCode = keySize*2 + 12;
	int header_size = sqlite3VarintLen(keyCode) + 8; // 8 is the maximum return value of sqlite3VarintLen(), so this is our worst case header size (for values larger than allowable database values)
	int hh = sqlite3VarintLen(header_size);
	header_size += hh;
	if (hh < sqlite3VarintLen(header_size))
		header_size++;
	return header_size + keySize + valuePrefixSize;
}


KeyValueRef decodeKV( StringRef encoded) {
	uint8_t const* d = encoded.begin();
	uint64_t h, len1, len2;
	d += sqlite3GetVarint( d, (u64*)&h );
	d += sqlite3GetVarint( d, (u64*)&len1 );
	d += sqlite3GetVarint( d, (u64*)&len2 );
	ASSERT( d == encoded.begin() + h );
	ASSERT( len1 >= 12 && !(len1&1) );
	ASSERT( len2 >= 12 && !(len2&1) );
	len1 = (len1-12)/2;
	len2 = (len2-12)/2;
	ASSERT( d + len1 + len2 == encoded.end() );
	return KeyValueRef( KeyRef(d, len1), KeyRef(d+len1, len2) );
}

// Given a key size and value prefix size, get the minimum bytes that must be read from the underlying
// btree tuple to safely read the prefix length from the value bytes (if the value is long enough)
int getEncodedKVFragmentSize( int keySize, int valuePrefixSize ) {
	int keyCode = keySize*2 + 12;
	int header_size = sqlite3VarintLen(keyCode)
				+ 1  // index code length
				+ 8; // worst case for value size (larger than fdb api allows)
	int hh = sqlite3VarintLen(header_size);
	header_size += hh;
	if (hh < sqlite3VarintLen(header_size))
		header_size++;
	return header_size + keySize
		+ 4  // Max width allowed of index value
		+ valuePrefixSize;
}

// Decode (key, index, value) tuple.
// A present() Optional will always be returned UNLESS partial is true.
// If partial is true then the return will not be present() unless at least
// the full key and index were in the encoded buffer.  The value returned will be 0 or
// more value bytes, however many were available.
// Note that a short encoded buffer must at *least* contain the header length varint.
Optional<KeyValueRef> decodeKVFragment( StringRef encoded, uint32_t *index = NULL, bool partial = false) {
	uint8_t const* d = encoded.begin();
	uint64_t h, len1, len2;
	d += sqlite3GetVarint( d, (u64*)&h );

	// Make sure entire header is present, else return nothing
	if(partial && encoded.size() < h)
		return Optional<KeyValueRef>();

	d += sqlite3GetVarint( d, (u64*)&len1 );
	const uint8_t indexLen = *d++;
	ASSERT(indexLen <= 4);
	d += sqlite3GetVarint( d, (u64*)&len2 );
	ASSERT( d == encoded.begin() + h );
	ASSERT( len1 >= 12 && !(len1&1) );
	ASSERT( len2 >= 12 && !(len2&1) );
	len1 = (len1-12)/2;
	len2 = (len2-12)/2;

	if(partial) {
		// If the key and index aren't complete, return nothing.
		if(d + len1 + indexLen > encoded.end())
			return Optional<KeyValueRef>();
		// Encoded size shouldn't be *larger* than the record described by the header no matter what.
		ASSERT( d + len1 + indexLen + len2 >= encoded.end() );
		// Shorten value length to be whatever bytes remain after the header/key/index
		len2 = std::min(len2, (uint64_t)(encoded.end() - indexLen - len1 - d));
	}
	else {
		// But for non partial records encoded size should be exactly the size of the described record.
		ASSERT( d + len1 + indexLen + len2 == encoded.end() );
	}

	// Decode big endian index
	if(index != nullptr) {
		if(indexLen == 0)
			*index = 0;
		else {
			const uint8_t *begin = d + len1;
			const uint8_t *end = begin + indexLen;
			*index = (uint8_t)*begin++;
			while(begin < end) {
				*index <<= 8;
				*index |= *begin++;
			}
		}
	}
	return KeyValueRef( KeyRef(d, len1), KeyRef(d+len1+indexLen, len2) );
}

KeyValueRef decodeKVPrefix( StringRef encoded, int maxLength ) {
	uint8_t const* d = encoded.begin();
	uint64_t h, len1, len2;
	d += sqlite3GetVarint( d, (u64*)&h );
	d += sqlite3GetVarint( d, (u64*)&len1 );
	d += sqlite3GetVarint( d, (u64*)&len2 );
	ASSERT( d == encoded.begin() + h );
	ASSERT( len1 >= 12 && !(len1&1) );
	ASSERT( len2 >= 12 && !(len2&1) );
	len1 = (len1-12)/2;
	len2 = (len2-12)/2;
	len2 = std::min(len2, (uint64_t)maxLength);
	ASSERT( d + len1 + len2 <= encoded.end() );
	return KeyValueRef( KeyRef(d, len1), KeyRef(d+len1, len2) );
}

Value encodeKey( KeyRef key, bool using_fragments) {
	int keyCode = key.size()*2 + 12;
	int header_size = sqlite3VarintLen(keyCode);
	if(using_fragments)  // will be encoded as key, 0  (where 0 is really a null)
		++header_size;
	int hh = sqlite3VarintLen(header_size);
	header_size += hh;
	if (hh < sqlite3VarintLen(header_size))
		header_size++;
	int size = header_size + key.size();
	Value v;
	uint8_t* d = new (v.arena()) uint8_t[size];
	((ValueRef&)v) = KeyRef(d, size);
	d += sqlite3PutVarint( d, header_size );
	d += sqlite3PutVarint( d, keyCode );
	if(using_fragments)
		*d++ = 0;
	memcpy(d, key.begin(), key.size());
	d += key.size();
	ASSERT( d == v.begin()+size );
	return v;
}

struct SQLiteTransaction {
	SQLiteDB& db;
	bool shouldCommit;
	SQLiteTransaction(SQLiteDB& db, bool write) : db(db), shouldCommit(false) {
		db.beginTransaction(write);
	}
	void commit() {
		shouldCommit = true;
	}
	~SQLiteTransaction() {
		try {
			if (shouldCommit)
				db.endTransaction();
			else
				db.rollback();
		} catch (...) {}
	}
};

struct IntKeyCursor {
	SQLiteDB& db;
	BtCursor *cursor;
	IntKeyCursor( SQLiteDB& db, int table, bool write ) : cursor(0), db(db) {
		cursor = (BtCursor*)new char[sqlite3BtreeCursorSize()];
		sqlite3BtreeCursorZero(cursor);
		db.checkError("BtreeCursor", sqlite3BtreeCursor(db.btree, table, write, NULL, cursor));
	}
	~IntKeyCursor() {
		if (cursor) {
			try {
				db.checkError("BtreeCloseCursor", sqlite3BtreeCloseCursor(cursor));
			} catch (...) {}
			delete[] (char*)cursor;
		}
	}
};

struct RawCursor {
	SQLiteDB& db;
	BtCursor *cursor;
	KeyInfo keyInfo;
	bool valid;

	operator bool() const { return valid; }

	RawCursor( SQLiteDB& db, int table, bool write) : cursor(0), db(db), valid(false) {
		keyInfo.db = db.db;
		keyInfo.enc = db.db->aDb[0].pSchema->enc;
		keyInfo.aColl[0] = db.db->pDfltColl;
		keyInfo.aSortOrder = 0;
		keyInfo.nField = 1;

		try {
			cursor = (BtCursor*)new char[sqlite3BtreeCursorSize()];
			sqlite3BtreeCursorZero(cursor);
			db.checkError("BtreeCursor", sqlite3BtreeCursor(db.btree, table, write, &keyInfo, cursor));
		} catch (...) {
			destroyCursor();
			throw;
		}
	}
	~RawCursor() {
		destroyCursor();
	}
	void destroyCursor() {
		if (cursor) {
			try {
				db.checkError("BtreeCloseCursor", sqlite3BtreeCloseCursor(cursor));
			} catch (...) {
				TraceEvent(SevError,"RawCursorDestructionError");
			}
			delete[] (char*)cursor;
		}
	}
	void moveFirst() {
		int empty=1;
		db.checkError("BtreeFirst", sqlite3BtreeFirst(cursor, &empty));
		valid = !empty;
	}
	void moveNext() {
		int empty=1;
		db.checkError("BtreeNext", sqlite3BtreeNext(cursor, &empty));
		valid = !empty;
	}
	void movePrevious() {
		int empty=1;
		db.checkError("BtreePrevious", sqlite3BtreePrevious(cursor, &empty));
		valid = !empty;
	}
	int size() {
		int64_t size;
		db.checkError("BtreeKeySize", sqlite3BtreeKeySize(cursor, (i64*)&size));
		ASSERT( size < (1<<30) );
		return size;
	}
	Value getEncodedRow() {
		int s = size();
		Value v;
		uint8_t* d = new (v.arena()) uint8_t[s];
		db.checkError("BtreeKey", sqlite3BtreeKey(cursor, 0, s, d));
		((ValueRef&)v) = KeyRef(d, s);
		return v;
	}
	ValueRef getEncodedRow( Arena& arena ) {
		int s = size();
		uint8_t* d = new (arena) uint8_t[s];
		db.checkError("BtreeKey", sqlite3BtreeKey(cursor, 0, s, d));
		return KeyRef(d, s);
	}
	ValueRef getEncodedRowPrefix( Arena& arena, int maxEncodedSize ) {
		int s = std::min(size(), maxEncodedSize);
		uint8_t* d = new (arena) uint8_t[s];
		db.checkError("BtreeKey", sqlite3BtreeKey(cursor, 0, s, d));
		return KeyRef(d, s);
	}
	void insertFragment( KeyValueRef kv, uint32_t index, int seekResult ) {
		Value v = encodeKVFragment(kv, index);
		db.checkError("BtreeInsert", sqlite3BtreeInsert(cursor, v.begin(), v.size(), NULL, 0, 0, 0, seekResult));
	}
	void remove() {
		db.checkError("BtreeDelete", sqlite3BtreeDelete(cursor));
	}
	void set( KeyValueRef kv ) {
		if(db.fragment_values) {
			// Unlike a read, where we need to access fragments in fully forward or reverse order,
			// here we just want to delete any existing fragments for the key.  It does not matter
			// what order we delete them in, and SQLite requires us to seek after every delete, so
			// the fastest way to do this is to repeatedly seek to the tuple prefix (key, ) and
			// delete the current fragment until nothing is there.
			// This should result in almost identical performance to non-fragmenting mode for single fragment kv pairs.
			int seekResult = moveTo(kv.key, true);   // second arg means to ignore fragmenting and seek to (key, )
			while(seekResult == 0) {
				remove();
				seekResult = moveTo(kv.key, true);
			}

			const int primaryPageUsable = SERVER_KNOBS->SQLITE_FRAGMENT_PRIMARY_PAGE_USABLE;
			const int overflowPageUsable = SERVER_KNOBS->SQLITE_FRAGMENT_OVERFLOW_PAGE_USABLE;

			int fragments = 1;
			int valuePerFragment = kv.value.size();

			// Figure out if we would benefit from fragmenting this kv pair.  The key size must be less than
			// primary page usable size, and the value and key size together must exceeed the primary page usable size.
			if(  (kv.key.size() + kv.value.size()) > primaryPageUsable
			   && kv.key.size() < primaryPageUsable) {

				// Just the part of the value that would be in a partially-filled overflow page
				int overflowPartialBytes = (kv.expectedSize() - primaryPageUsable) % overflowPageUsable;

				// Number of bytes wasted in the unfragmented case
				int unfragmentedWaste = overflowPageUsable - overflowPartialBytes;

				// Total space used for unfragmented form
				int unfragmentedTotal = kv.expectedSize() + unfragmentedWaste;

				// Value bytes that can fit in the primary page for each fragment
				int primaryPageValueBytes = primaryPageUsable - kv.key.size();

				// Calculate how many total fragments it would take to spread the partial overflow page bytes and the first fragment's primary
				// page value bytes evenly over multiple tuples that fit in primary pages.
				fragments = (primaryPageValueBytes + overflowPartialBytes + primaryPageValueBytes - 1) / primaryPageValueBytes;

				// Number of bytes wasted in the fragmented case (for the extra key copies)
				int fragmentedWaste = kv.key.size() * (fragments - 1);

				// Total bytes used for the fragmented case
				//int fragmentedTotal = kv.expectedSize() + fragmentedWaste;

				// Calculate bytes saved by having extra key instances stored vs the original partial overflow page bytes.
				int savings = unfragmentedWaste - fragmentedWaste;

				double reduction = (double)savings / unfragmentedTotal;

				//printf("K: %5d  V: %6d  OVERFLOW: %5d  FRAGMENTS: %3d  SAVINGS: %4d  FRAG: %7d  UNFRAG: %7d  REDUCTION: %.3f\n",
					//kv.key.size(), kv.value.size(), overflowPartialBytes, fragments, savings, fragmentedTotal, unfragmentedTotal, reduction);
				if(reduction < SERVER_KNOBS->SQLITE_FRAGMENT_MIN_SAVINGS)
					fragments = 1;
				else
					valuePerFragment = (primaryPageValueBytes + overflowPartialBytes + fragments - 1) / fragments;
			}

			if(fragments == 1) {
				insertFragment(kv, 0, seekResult);
				return;
			}

			// First index is ceiling(value_size / KV_FRAGMENT_INDEX_SIZE_HINT_FACTOR)
			uint32_t nextIndex = (kv.value.size() + KV_FRAGMENT_INDEX_SIZE_HINT_FACTOR - 1) / KV_FRAGMENT_INDEX_SIZE_HINT_FACTOR;
			// Last index is ceiling(value_size / (KV_FRAGMENT_INDEX_SIZE_HINT_FACTOR / 2) )
			uint32_t finalIndex = (kv.value.size() + (KV_FRAGMENT_INDEX_SIZE_HINT_FACTOR / 2) - 1) / (KV_FRAGMENT_INDEX_SIZE_HINT_FACTOR / 2);
			int bytesLeft = kv.value.size();
			int readPos = 0;
			while(bytesLeft > 0) {
				--fragments;  // remaining ideal fragment count
				int fragSize = (fragments == 0) ? bytesLeft : std::min<int>(bytesLeft, valuePerFragment);

				// The last fragment must have an index of finalIndex or higher.
				if(fragSize == bytesLeft && nextIndex < finalIndex)
					nextIndex = finalIndex;
				//printf("insert ks %d vs %d  fragment %d, %dbytes\n", kv.key.size(), kv.value.size(), nextIndex, fragSize);
				insertFragment(KeyValueRef(kv.key, kv.value.substr(readPos, fragSize)), nextIndex, seekResult);
				// seekResult can only be used for the first insertion.
				if(seekResult != 0)
					seekResult = 0;
				readPos += fragSize;
				bytesLeft -= fragSize;
				++nextIndex;
			}
		}
		else {
			int r = moveTo( kv.key );
			if (!r) remove();
			Value v = encode(kv);
			db.checkError("BTreeInsert", sqlite3BtreeInsert(cursor, v.begin(), v.size(), NULL, 0, 0, 0, r));
		}
	}
	void clearOne( KeyRangeRef keys ) {
		ASSERT(!db.fragment_values);
		int r = moveTo( keys.begin );
		if (r < 0) moveNext();
		ASSERT( valid && decodeKV(getEncodedRow()).key < keys.end );
		remove();
	}
	void clear( KeyRangeRef keys ) {
		// TODO: This is really slow!
		while (true) {
			int r = moveTo( keys.begin );
			if (r < 0) moveNext();
			if (!valid || (db.fragment_values ? decodeKVFragment(getEncodedRow()).get().key : decodeKV(getEncodedRow()).key) >= keys.end)
				break;
			remove();
		}
	}
	void fastClear( KeyRangeRef keys, bool& freeTableEmpty ) {
		vector<int> clearBuffer( SERVER_KNOBS->CLEAR_BUFFER_SIZE );
		clearBuffer[0] = 0;

		while (true) {
			if (moveTo( keys.begin )<0) moveNext();
			RawCursor endCursor(db, db.table, false);
			if (endCursor.moveTo( keys.end )>=0) endCursor.movePrevious();

			if (!valid || !endCursor
				|| (db.fragment_values ? (decodeKVFragment(getEncodedRow()).get().key >= decodeKVFragment(endCursor.getEncodedRow()).get().key)
				                    : (decodeKV(getEncodedRow()).key > decodeKV(endCursor.getEncodedRow()).key)
				   )
			)
				break;  // If empty stop!

			int rc = sqlite3BtreeDeleteRange(cursor, endCursor.cursor, &clearBuffer[0], &clearBuffer[0]+clearBuffer.size());
			if (rc == 201) continue;
			if (!rc) break;
			db.checkError("BtreeDeleteRange", rc);
		}

		if (clearBuffer[0]) {
			//printf("fastClear(%s,%s): %d pages freed\n", printable(keys.begin).c_str(), printable(keys.end).c_str(), clearBuffer[0]);
			IntKeyCursor fc(db, db.freetable, true);
			int pagesDeleted = 0;
			db.checkError( "BtreeLazyDelete", sqlite3BtreeLazyDelete( fc.cursor, &clearBuffer[0], &clearBuffer[0]+clearBuffer.size(), 0, &pagesDeleted ) );
			ASSERT(pagesDeleted == 0);
			freeTableEmpty = false;
		}
	}
	int lazyDelete( int desiredPages ) {
		vector<int> clearBuffer( SERVER_KNOBS->CLEAR_BUFFER_SIZE );
		clearBuffer[0] = 0;

		IntKeyCursor fc(db, db.freetable, true);
		int pagesDeleted = 0;
		db.checkError( "BtreeLazyDelete", sqlite3BtreeLazyDelete( fc.cursor, &clearBuffer[0], &clearBuffer[0]+clearBuffer.size(), desiredPages, &pagesDeleted ));
		return pagesDeleted;
	}

	// Reads and reconstitutes kv fragments given cursor, an arena to allocate in, and a direction to move the cursor.
	//   getNext() returns the next KV pair, if there is one
	//   peek() returns the next key that would be read by getNext(), if there is one
	// Both methods return Optionals.
	// Once either method returns a non-present value, using the DefragmentingReader again is undefined behavior.
	struct DefragmentingReader {
		// Use this constructor for forward/backward range reads
		DefragmentingReader(RawCursor &cur, Arena &m, bool forward) : cur(cur), arena(m), forward(forward), fragmentReadLimit(-1) {
			parse();
		}

		// Use this constructor to read a SINGLE partial value from the current cursor position for an expected key.
		// This exists to support IKeyValueStore::getPrefix().
		// The reader will return exactly one KV pair if its key matches expectedKey, otherwise no KV pairs.
		DefragmentingReader(RawCursor &cur, Arena &m, KeyRef expectedKey, int maxValueLen): cur(cur), arena(m), forward(true), maxValueLen(maxValueLen) {
			fragmentReadLimit = getEncodedKVFragmentSize(expectedKey.size(), maxValueLen);
			parse();
			// If a key was found but it wasn't the expected key then
			// clear the current kv pair and invalidate the cursor.
			if(kv.present() && kv.get().key != expectedKey) {
				kv = Optional<KeyValueRef>();
				cur.valid = false;
			}
		}

	private:
		Optional<KeyValueRef> kv;  // key and latest value fragment read
		uint32_t index;            // index of latest value fragment read
		RawCursor &cur;            // Cursor to read from
		Arena &arena;              // Arena to allocate key and value bytes in
		bool forward;              // true for forward iteration, false for reverse
		int maxValueLen;           // truncated value length to return
		int fragmentReadLimit;     // If >= 0, only read and *attempt* to decode this many fragment bytes

		// Update kv with whatever is at the current cursor position if the position is valid.
		void parse() {
			if(cur.valid) {
				// The read is either not partial or it is but the fragment read limit is at least 4 (the size of a minimal header).
				bool partial = fragmentReadLimit >= 0;
				ASSERT(!partial || fragmentReadLimit >= 4);
				// Read full or part of fragment
				ValueRef encoded = (partial) ? cur.getEncodedRowPrefix(arena, fragmentReadLimit) : cur.getEncodedRow(arena);
				kv = decodeKVFragment(encoded, &index, partial);
				// If this was a partial fragment then if successful update the next fragment read size, and if not
				// then invalidate the cursor.
				if(partial) {
					if(kv.present())
						fragmentReadLimit -= kv.get().value.size();
					else
						cur.valid = false;
				}
			}
			else
				kv = Optional<KeyValueRef>();
		}

		// advance cursor, parse and return key if valid
		Optional<KeyRef> advance() {
			if(cur.valid) {
				forward ? cur.moveNext() : cur.movePrevious();
				parse();
			}
			return kv.present() ? kv.get().key : Optional<KeyRef>();
		}

	public:
		// Get the next key that would be returned by getNext(), if there is one
		// This is more efficient than getNext() if the caller is not sure if it wants the next KV pair
		Optional<KeyRef> peek() {
			if(kv.present())
				return kv.get().key;
			return advance();
		}

		Optional<KeyValueRef> getNext() {
			if(!peek().present())
				return Optional<KeyValueRef>();

			bool partial = fragmentReadLimit >= 0;

			// Start out with the next KV fragment as the pair to return
			KeyValueRef resultKV = kv.get();

			// If index is 0 then this is an unfragmented key.  It is unnecessary to advance the cursor so
			// we won't, but we will clear kv so that the next peek/getNext will have to advance.
			if(index == 0)
				kv = Optional<KeyValueRef>();
			else {
				// First and last indexes in fragment group are size hints.
				//   First index is ceil(total_value_size / 4)
				//   Last  index is ceil(total_value_size / 2)
				// Set size depending on which of these will be first encountered and allocate buffer in arena.
				// Note that if these index hints are wrong (such as if the index scheme changes) then asserts
				// below will fail.  They will have to be changed to expand the buffer as needed.
				int size = forward ? (index * KV_FRAGMENT_INDEX_SIZE_HINT_FACTOR) : (index * (KV_FRAGMENT_INDEX_SIZE_HINT_FACTOR / 2));
				uint8_t *buf = new (arena) uint8_t[size];
				uint8_t *bufEnd = buf + size;
				// For forward iteration wptr is the place to write to next, for reverse it's where the last write started.
				uint8_t *wptr = forward ? buf : bufEnd;
				int fragments = 0;
				do {
					++fragments;
					const ValueRef &val = kv.get().value;
					if(forward) {
						uint8_t *w = wptr;
						wptr += val.size();
						ASSERT(wptr <= bufEnd);
						memcpy(w, val.begin(), val.size());
						// If this is a partial value get and we have enough bytes we can stop since we are forward iterating.
						if(partial && wptr - buf >= maxValueLen) {
							resultKV.value = ValueRef(buf, maxValueLen);
							// To make further calls to peek() or getNext() return nothing, reset kv and invalidate cursor
							kv = Optional<KeyValueRef>();
							cur.valid = false;
							return resultKV;
						}
					}
					else {
						wptr -= val.size();
						ASSERT(wptr >= buf);
						memcpy(wptr, val.begin(), val.size());
					}
				} while(advance().present() && kv.get().key == resultKV.key);

				// If there was only 1 fragment, it should have been index 0 and handled above,
				ASSERT(fragments != 1);
				// Set final value based on direction of buffer fill
				resultKV.value = forward ? ValueRef(buf, wptr - buf) : ValueRef(wptr, bufEnd - wptr);
			}

			// In partial value mode, we could end up here if there was only 1 fragments or maxValueLen
			// was greater than the total unfragmented value size.
			if(partial)
				resultKV.value = resultKV.value.substr(0, std::min(resultKV.value.size(), maxValueLen));
			return resultKV;
		}
	};

	Optional<Value> get( KeyRef key ) {
		int r = moveTo(key);
		if(db.fragment_values) {
			// Optimization - moveTo seeks to fragment (key, 0) so if it was exactly found then we
			// know we have a single fragment for key and can return it.
			if(r == 0) {
				Value result;
				((ValueRef&)result) = decodeKVFragment(getEncodedRow(result.arena())).get().value;
				return result;
			}

			// Otherwise see if the fragments immediately after (key, 0) are for the key we want.
			if(r < 0)
				moveNext();
			Arena m;
			DefragmentingReader i(*this, m, true);
			if(i.peek() == key) {
				Optional<KeyValueRef> kv = i.getNext();
				return Value(kv.get().value, m);
			}
		}
		else if (r == 0) {
			Value result;
			KeyValueRef kv = decodeKV( getEncodedRow( result.arena() ) );
			((ValueRef&)result) = kv.value;
			return result;
		}

		return Optional<Value>();
	}
	Optional<Value> getPrefix( KeyRef key, int maxLength ) {
		if(db.fragment_values) {
			int r = moveTo(key);
			if (r < 0)
				moveNext();
			Arena m;
			DefragmentingReader i(*this, m, getEncodedKVFragmentSize(key.size(), maxLength));
			if(i.peek() == key) {
				Optional<KeyValueRef> kv = i.getNext();
				return Value(kv.get().value, m);
			}
		}
		else if (!moveTo(key)) {
			if(maxLength == 0) {
				return Value();
			}
			Value result;
			int maxEncodedSize = getEncodedSize( key.size(), maxLength );
			KeyValueRef kv = decodeKVPrefix( getEncodedRowPrefix( result.arena(), maxEncodedSize ), maxLength );
			((ValueRef&)result) = kv.value;
			return result;
		}
		return Optional<Value>();
	}
	Standalone<VectorRef<KeyValueRef>> getRange( KeyRangeRef keys, int rowLimit, int byteLimit ) {
		Standalone<VectorRef<KeyValueRef>> result;
		int accumulatedBytes = 0;
		ASSERT( byteLimit > 0 );
		if(db.fragment_values) {
			if(rowLimit >= 0) {
				int r = moveTo(keys.begin);
				if (r < 0)
					moveNext();

				DefragmentingReader i(*this, result.arena(), true);
				Optional<KeyRef> nextKey = i.peek();
				while(nextKey.present() && nextKey.get() < keys.end && rowLimit-- && accumulatedBytes < byteLimit) {
					Optional<KeyValueRef> kv = i.getNext();
					result.push_back(result.arena(), kv.get());
					accumulatedBytes += sizeof(KeyValueRef) + kv.get().expectedSize();
					nextKey = i.peek();
				}
			}
			else {
				int r = moveTo(keys.end);
				if (r >= 0)
					movePrevious();
				DefragmentingReader i(*this, result.arena(), false);
				Optional<KeyRef> nextKey = i.peek();
				while(nextKey.present() && nextKey.get() >= keys.begin && rowLimit++ && accumulatedBytes < byteLimit) {
					Optional<KeyValueRef> kv = i.getNext();
					result.push_back(result.arena(), kv.get());
					accumulatedBytes += sizeof(KeyValueRef) + kv.get().expectedSize();
					nextKey = i.peek();
				}
			}
		}
		else {
			if (rowLimit >= 0) {
				int r = moveTo( keys.begin );
				if (r < 0) moveNext();
				while (this->valid && rowLimit-- && accumulatedBytes < byteLimit) {
					KeyValueRef kv = decodeKV( getEncodedRow( result.arena() ) );
					accumulatedBytes += sizeof(KeyValueRef) + kv.expectedSize();
					if (kv.key >= keys.end) break;
					result.push_back( result.arena(), kv );
					moveNext();
				}
			} else {
				int r = moveTo( keys.end );
				if (r >= 0) movePrevious();
				while (this->valid && rowLimit++ && accumulatedBytes < byteLimit) {
					KeyValueRef kv = decodeKV( getEncodedRow( result.arena() ) );
					accumulatedBytes += sizeof(KeyValueRef) + kv.expectedSize();
					if (kv.key < keys.begin) break;
					result.push_back( result.arena(), kv );
					movePrevious();
				}
			}
		}
		return result;
	}

	int moveTo( KeyRef key, bool ignore_fragment_mode = false ) {
		UnpackedRecord r;
		r.pKeyInfo = &keyInfo;
		r.flags = UNPACKED_PREFIX_MATCH;  // This record [key] can be considered equal to a record [key,value] for any value
		Mem tupleValues[2];
		r.aMem = tupleValues;

		// Set field 1 of tuple to key, which is a string type with typecode 12 + 2*len
		tupleValues[0].db = keyInfo.db;
		tupleValues[0].enc = keyInfo.enc;
		tupleValues[0].zMalloc = NULL;
		ASSERT(sqlite3VdbeSerialGet(key.begin(), 12 + (2 * key.size()), &tupleValues[0]) == key.size());

		// In fragmenting mode, seek is to (k, 0, ), otherwise just (k, ).
		if(ignore_fragment_mode || !db.fragment_values)
			r.nField = 1;
		else {
			// Set field 2 of tuple to the null type which is typecode 0
			tupleValues[1].db = keyInfo.db;
			tupleValues[1].enc = keyInfo.enc;
			tupleValues[1].zMalloc = NULL;
			ASSERT(sqlite3VdbeSerialGet(NULL, 0, &tupleValues[1]) == 0);

			r.nField = 2;
		}

		int result;
		db.checkError("BtreeMovetoUnpacked", sqlite3BtreeMovetoUnpacked(cursor, &r, 0, 0, &result));
		valid = result >= 0 || !sqlite3BtreeEof(cursor);
		return result;
	}
};
struct Cursor : SQLiteTransaction, RawCursor {
	Cursor( SQLiteDB& db, bool write) : SQLiteTransaction(db, write), RawCursor(db, db.table, write) {

	}
};

struct ReadCursor : ReferenceCounted<ReadCursor>, FastAllocated<ReadCursor> {
	// Readers need to be reset (forced to move to a new snapshot) when the writer thread does a checkpoint.
	// ReadCursor is reference counted so that the writer can clear the persistent reference (readCursors[n]) and
	//   readers can hold an additional reference when they actually have a read happening.
	// ReadCursor lazily constructs its actual Cursor (and hence transaction) because it's vital that readCursors[n] be
	//   assigned before the transaction is opened.

	ReadCursor() : valid(false) {}

	void init(SQLiteDB& db) { new (&cursor) Cursor(db, false); valid = true; }
	~ReadCursor() { if (valid) get().~Cursor(); }

	Cursor& get() { return *((Cursor*)&cursor); }

private:
	std::aligned_storage< sizeof(Cursor), __alignof(Cursor) >::type cursor;
	bool valid;
};

extern bool vfsAsyncIsOpen( std::string filename );

// Returns number of pages which failed checksum.
int SQLiteDB::checkAllPageChecksums() {
	ASSERT( !haveMutex );
	ASSERT( page_checksums );  // This should never be called on SQLite databases that do not have page checksums.

	double startT = timer();

	// First try to open an existing file
	std::string apath = abspath(filename);
	std::string walpath = apath + "-wal";

	/* REMOVE THIS BEFORE CHECKIN */ if(!fileExists(apath)) return 0;

	TraceEvent("SQLitePageChecksumScanBegin").detail("File", apath);

	ErrorOr<Reference<IAsyncFile>> dbFile = waitForAndGet( errorOr( IAsyncFileSystem::filesystem()->open( apath, IAsyncFile::OPEN_READONLY | IAsyncFile::OPEN_LOCK, 0 ) ) );
	ErrorOr<Reference<IAsyncFile>> walFile = waitForAndGet( errorOr( IAsyncFileSystem::filesystem()->open( walpath, IAsyncFile::OPEN_READONLY | IAsyncFile::OPEN_LOCK, 0 ) ) );

	if (dbFile.isError()) throw dbFile.getError(); // If we've failed to open the file, throw an exception
	if (walFile.isError()) throw walFile.getError(); // If we've failed to open the file, throw an exception

	// Now that the file itself is open and locked, let sqlite open the database
	// Note that VFSAsync will also call g_network->open (including for the WAL), so its flags are important, too
	// TODO:  If better performance is needed, make AsyncFileReadAheadCache work and be enabled by SQLITE_OPEN_READAHEAD which was added for that purpose.
	int result = sqlite3_open_v2(apath.c_str(), &db, SQLITE_OPEN_READONLY, NULL);
	checkError("open", result);

	// This check has the useful side effect of actually opening/reading the database.  If we were not doing this,
	// then we could instead open a read cursor for the same effect, as currently tryReadEveryDbPage() requires it.
	Statement *jm = new Statement(*this, "PRAGMA journal_mode");
	ASSERT( jm->nextRow() );
	if (jm->column(0) != LiteralStringRef("wal")){
		TraceEvent(SevError, "JournalModeError").detail("Filename", filename).detail("Mode", jm->column(0));
		ASSERT( false );
	}
	delete jm;

	btree = db->aDb[0].pBt;
	initPagerCodec();
	sqlite3_extended_result_codes(db, 1);

	sqlite3_mutex_enter(db->mutex);
	haveMutex = true;

	pPagerCodec->silent = true;
	Pgno p = 1;
	int readErrors = 0;
	int corruptPages = 0;
	int totalErrors = 0;

	while(1) {
		int type;
		int zero;
		int rc = tryReadEveryDbPage(db, p, &p, &type, &zero);
		if(rc == SQLITE_OK)
			break;
		if(rc == SQLITE_CORRUPT) {
			TraceEvent(SevWarnAlways, "SQLitePageChecksumScanCorruptPage")
				.detail("File", filename)
				.detail("PageNumber", p)
				.detail("PageType", type)
				.detail("PageWasZeroed", zero);
			++corruptPages;
		} else {
			TraceEvent(SevWarnAlways, "SQLitePageChecksumScanReadFailed")
				.detail("File", filename)
				.detail("PageNumber", p)
				.detail("SQLiteError", sqlite3ErrStr(rc))
				.detail("SQLiteErrorCode", rc);
			++readErrors;
		}
		++p;
		if(++totalErrors >= SERVER_KNOBS->SQLITE_PAGE_SCAN_ERROR_LIMIT)
			break;
	}
	pPagerCodec->silent = false;

	haveMutex = false;
	sqlite3_mutex_leave(db->mutex);
	sqlite3_close(db);

	TraceEvent("SQLitePageChecksumScanEnd")
		.detail("Elapsed", DEBUG_DETERMINISM ? 0 : timer()-startT)
		.detail("Filename", filename)
		.detail("CorruptPages", corruptPages)
		.detail("ReadErrors", readErrors)
		.detail("TotalErrors", totalErrors);

	ASSERT(!vfsAsyncIsOpen(filename));

	return totalErrors;
}

void SQLiteDB::open(bool writable) {
	ASSERT( !haveMutex );
	double startT = timer();
	//TraceEvent("KVThreadInitStage").detail("Stage",1).detail("Filename", filename).detail("Writable", writable);

	// First try to open an existing file
	std::string apath = abspath(filename);
	std::string walpath = apath + "-wal";
	ErrorOr<Reference<IAsyncFile>> dbFile = waitForAndGet( errorOr( IAsyncFileSystem::filesystem()->open( apath, IAsyncFile::OPEN_READWRITE | IAsyncFile::OPEN_LOCK, 0 ) ) );
	ErrorOr<Reference<IAsyncFile>> walFile = waitForAndGet( errorOr( IAsyncFileSystem::filesystem()->open( walpath, IAsyncFile::OPEN_READWRITE | IAsyncFile::OPEN_LOCK, 0 ) ) );

	//TraceEvent("KVThreadInitStage").detail("Stage",15).detail("Filename", apath).detail("Writable", writable).detail("IsErr", dbFile.isError());

	if (writable) {
		if (dbFile.isError() && dbFile.getError().code() == error_code_file_not_found && !fileExists(apath) && // db file is missing
			!walFile.isError() && fileExists(walpath)) // ..but WAL file is present
		{
			// Either we died partway through creating this DB, or died partway through deleting it, or someone is monkeying with our files
			// Create a new blank DB by backing up the WAL file (just in case it is important) and then hitting the next case
			walFile = file_not_found();
			renameFile( walpath, walpath + "-old-" + deterministicRandom()->randomUniqueID().toString() );
			ASSERT_WE_THINK(false);  //< This code should not be hit in FoundationDB at the moment, because worker looks for databases to open by listing .fdb files, not .fdb-wal files
			//TEST(true);  // Replace a partially constructed or destructed DB
		}

		if (dbFile.isError() && walFile.isError() && writable &&
			dbFile.getError().code() == error_code_file_not_found &&
			walFile.getError().code() == error_code_file_not_found &&
			!fileExists(apath) && !fileExists(walpath))
		{
			// The file doesn't exist, try to create a new one
			// Creating the WAL before the database ensures we will not try to open a database with no WAL
			walFile = waitForAndGet( IAsyncFileSystem::filesystem()->open( walpath, IAsyncFile::OPEN_ATOMIC_WRITE_AND_CREATE | IAsyncFile::OPEN_CREATE | IAsyncFile::OPEN_READWRITE | IAsyncFile::OPEN_LOCK, 0600 ) );
			waitFor( walFile.get()->sync() );
			dbFile = waitForAndGet( IAsyncFileSystem::filesystem()->open( apath, IAsyncFile::OPEN_ATOMIC_WRITE_AND_CREATE | IAsyncFile::OPEN_CREATE | IAsyncFile::OPEN_READWRITE | IAsyncFile::OPEN_LOCK, 0600 ) );
			if(page_checksums)
				waitFor( dbFile.get()->write( template_fdb_with_page_checksums, sizeof(template_fdb_with_page_checksums), 0 ) );
			else
				waitFor( dbFile.get()->write( template_fdb_without_page_checksums, sizeof(template_fdb_without_page_checksums), 0 ) );
			waitFor( dbFile.get()->sync() ); // renames filename.part to filename, fsyncs data and directory
			TraceEvent("CreatedDBFile").detail("Filename", apath);
		}
	}
	if (dbFile.isError()) throw dbFile.getError(); // If we've failed to open the file, throw an exception
	if (walFile.isError()) throw walFile.getError(); // If we've failed to open the file, throw an exception

	//TraceEvent("KVThreadInitStage").detail("Stage",2).detail("Filename", filename).detail("Writable", writable);

	// Now that the file itself is open and locked, let sqlite open the database
	// Note that VFSAsync will also call g_network->open (including for the WAL), so its flags are important, too
	int result = sqlite3_open_v2(apath.c_str(), &db, (writable ? SQLITE_OPEN_READWRITE : SQLITE_OPEN_READONLY), NULL);
	checkError("open", result);

	int chunkSize;
	if( !g_network->isSimulated() ) {
		chunkSize = 4096 * SERVER_KNOBS->SQLITE_CHUNK_SIZE_PAGES;
	} else if( BUGGIFY ) {
		chunkSize = 4096 * deterministicRandom()->randomInt(0, 100);
	} else {
		chunkSize = 4096 * SERVER_KNOBS->SQLITE_CHUNK_SIZE_PAGES_SIM;
	}
	checkError("setChunkSize", sqlite3_file_control(db, nullptr, SQLITE_FCNTL_CHUNK_SIZE, &chunkSize));

	btree = db->aDb[0].pBt;
	initPagerCodec();

	sqlite3_extended_result_codes(db, 1);

	//TraceEvent("KVThreadInitStage").detail("Stage",3).detail("Filename", filename).detail("Writable", writable);

	//Statement(*this, "PRAGMA cache_size = 100").execute();

	Statement jm(*this, "PRAGMA journal_mode");
	ASSERT( jm.nextRow() );
	if (jm.column(0) != LiteralStringRef("wal")){
		TraceEvent(SevError, "JournalModeError").detail("Filename", filename).detail("Mode", jm.column(0));
		ASSERT( false );
	}

	if (writable) {
		Statement(*this, "PRAGMA synchronous = NORMAL").execute(); // OFF, NORMAL, FULL
		Statement(*this, "PRAGMA wal_autocheckpoint = -1").nextRow();
	}

	//TraceEvent("KVThreadInitStage").detail("Stage",4).detail("Filename", filename).detail("Writable", writable);

	sqlite3_mutex_enter(db->mutex);
	haveMutex = true;

	table = 3;
	freetable = 4;
	this->dbFile = dbFile.get();
	this->walFile = walFile.get();

	TraceEvent("KVThreadInitTime").detail("Elapsed", DEBUG_DETERMINISM ? 0 : timer()-startT).detail("Filename", filename).detail("Writable", writable);
	ASSERT(vfsAsyncIsOpen(filename));
}

void SQLiteDB::createFromScratch() {
	int sqliteFlags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE;
	checkError("open", sqlite3_open_v2(filename.c_str(), &db, sqliteFlags, NULL));

	Statement(*this, "PRAGMA page_size = 4096").nextRow(); //fast
	btree = db->aDb[0].pBt;
	initPagerCodec();

	Statement(*this, "PRAGMA auto_vacuum = 2").nextRow(); //slow all the time
	Statement(*this, "PRAGMA journal_mode = WAL").nextRow(); // sometimes slow
	sqlite3_extended_result_codes(db, 1);

	sqlite3_mutex_enter(db->mutex);
	haveMutex = true;

	beginTransaction(true);
	u32 pgnoRoot = -1;
	sqlite3BtreeGetMeta(btree, BTREE_LARGEST_ROOT_PAGE, &pgnoRoot);

	// We expect our tables are #3, #4 (since autovacuum is enabled, there is a pointer map page at #2)
	if (pgnoRoot == 4) {
		table = pgnoRoot-1;
		freetable = pgnoRoot;
		rollback();
	} else if (pgnoRoot == 1){
		// The database is empty; create tables
		checkError("BtreeCreateTable", sqlite3BtreeCreateTable( btree, &table, BTREE_BLOBKEY ));
		ASSERT( table == 3 );
		checkError("BtreeCreateTable2", sqlite3BtreeCreateTable( btree, &freetable, BTREE_INTKEY ));
		ASSERT( freetable == table+1 );
		endTransaction();
	} else {
		TraceEvent("PgnoRoot").detail("Value", pgnoRoot);
		checkError("CheckTables", SQLITE_CORRUPT);
	}
}

struct ThreadSafeCounter {
	volatile int64_t counter;
	ThreadSafeCounter() : counter(0) {}
	void operator ++() { interlockedIncrement64(&counter); }
	void operator --() { interlockedDecrement64(&counter); }
	operator const int64_t() const { return counter; }
};

class KeyValueStoreSQLite : public IKeyValueStore {
public:
	virtual void dispose() {
		doClose(this, true);
	}
	virtual void close() {
		doClose(this, false);
	}

	virtual Future<Void> getError() { return delayed( readThreads->getError() || writeThread->getError() ); }
	virtual Future<Void> onClosed() { return stopped.getFuture(); }

	virtual KeyValueStoreType getType() { return type; }
	virtual StorageBytes getStorageBytes();

	virtual void set( KeyValueRef keyValue, const Arena* arena = NULL );
	virtual void clear( KeyRangeRef range, const Arena* arena = NULL );
	virtual Future<Void> commit(bool sequential = false);

	virtual Future<Optional<Value>> readValue( KeyRef key, Optional<UID> debugID );
	virtual Future<Optional<Value>> readValuePrefix( KeyRef key, int maxLength, Optional<UID> debugID );
	virtual Future<Standalone<VectorRef<KeyValueRef>>> readRange( KeyRangeRef keys, int rowLimit = 1<<30, int byteLimit = 1<<30 );

	KeyValueStoreSQLite(std::string const& filename, UID logID, KeyValueStoreType type, bool checkChecksums, bool checkIntegrity);
	~KeyValueStoreSQLite();

	struct SpringCleaningWorkPerformed {
		int lazyDeletePages = 0;
		int vacuumedPages = 0;
	};

	Future<SpringCleaningWorkPerformed> doClean();
	void startReadThreads();

private:
	KeyValueStoreType type;
	UID logID;
	std::string filename;
	Reference<IThreadPool> readThreads, writeThread;
	Promise<Void> stopped;
	Future<Void> cleaning, logging, starting, stopOnErr;

	int64_t readsRequested, writesRequested;
	ThreadSafeCounter readsComplete;
	volatile int64_t writesComplete;
	volatile SpringCleaningStats springCleaningStats;
	volatile int64_t diskBytesUsed;
	volatile int64_t freeListPages;

	vector< Reference<ReadCursor> > readCursors;

	struct Reader : IThreadPoolReceiver {
		SQLiteDB conn;
		ThreadSafeCounter& counter;
		UID dbgid;
		Reference<ReadCursor>* ppReadCursor;

		explicit Reader( std::string const& filename, bool is_btree_v2, ThreadSafeCounter& counter, UID dbgid, Reference<ReadCursor>* ppReadCursor )
			: conn( filename, is_btree_v2, is_btree_v2 ), counter(counter), dbgid(dbgid), ppReadCursor(ppReadCursor)
		{
		}
		~Reader() {
			ppReadCursor->clear();
		}

		virtual void init() {
			conn.open(false);
		}

		Reference<ReadCursor> getCursor() {
			Reference<ReadCursor> cursor = *ppReadCursor;
			if (!cursor) {
				*ppReadCursor = cursor = Reference<ReadCursor>(new ReadCursor);
				cursor->init(conn);
			}
			return cursor;
		}

		struct ReadValueAction : TypedAction<Reader, ReadValueAction>, FastAllocated<ReadValueAction> {
			Key key;
			Optional<UID> debugID;
			ThreadReturnPromise<Optional<Value>> result;
			ReadValueAction(Key key, Optional<UID> debugID) : key(key), debugID(debugID) {};
			virtual double getTimeEstimate() { return SERVER_KNOBS->READ_VALUE_TIME_ESTIMATE; }
		};
		void action( ReadValueAction& rv ) {
			//double t = timer();
			if (rv.debugID.present()) g_traceBatch.addEvent("GetValueDebug", rv.debugID.get().first(), "Reader.Before"); //.detail("TaskID", g_network->getCurrentTask());

			rv.result.send( getCursor()->get().get(rv.key) );
			++counter;

			if (rv.debugID.present()) g_traceBatch.addEvent("GetValueDebug", rv.debugID.get().first(), "Reader.After"); //.detail("TaskID", g_network->getCurrentTask());
			//t = timer()-t;
			//if (t >= 1.0) TraceEvent("ReadValueActionSlow",dbgid).detail("Elapsed", t);
		}

		struct ReadValuePrefixAction : TypedAction<Reader, ReadValuePrefixAction>, FastAllocated<ReadValuePrefixAction> {
			Key key;
			int maxLength;
			Optional<UID> debugID;
			ThreadReturnPromise<Optional<Value>> result;
			ReadValuePrefixAction(Key key, int maxLength, Optional<UID> debugID) : key(key), maxLength(maxLength), debugID(debugID) {};
			virtual double getTimeEstimate() { return SERVER_KNOBS->READ_VALUE_TIME_ESTIMATE; }
		};
		void action( ReadValuePrefixAction& rv ) {
			//double t = timer();
			if (rv.debugID.present()) g_traceBatch.addEvent("GetValuePrefixDebug", rv.debugID.get().first(), "Reader.Before"); //.detail("TaskID", g_network->getCurrentTask());

			rv.result.send( getCursor()->get().getPrefix(rv.key, rv.maxLength) );
			++counter;

			if (rv.debugID.present()) g_traceBatch.addEvent("GetValuePrefixDebug", rv.debugID.get().first(), "Reader.After"); //.detail("TaskID", g_network->getCurrentTask());
			//t = timer()-t;
			//if (t >= 1.0) TraceEvent("ReadValuePrefixActionSlow",dbgid).detail("Elapsed", t);
		}

		struct ReadRangeAction : TypedAction<Reader, ReadRangeAction>, FastAllocated<ReadRangeAction> {
			KeyRange keys;
			int rowLimit, byteLimit;
			ThreadReturnPromise<Standalone<VectorRef<KeyValueRef>>> result;
			ReadRangeAction(KeyRange keys, int rowLimit, int byteLimit) : keys(keys), rowLimit(rowLimit), byteLimit(byteLimit) {}
			virtual double getTimeEstimate() { return SERVER_KNOBS->READ_RANGE_TIME_ESTIMATE; }
		};
		void action( ReadRangeAction& rr ) {
			rr.result.send( getCursor()->get().getRange(rr.keys, rr.rowLimit, rr.byteLimit) );
			++counter;
		}
	};

	struct Writer : IThreadPoolReceiver {
		SQLiteDB conn;
		Cursor* cursor;
		int commits;
		int setsThisCommit;
		bool freeTableEmpty; // true if we are sure the freetable (pages pending lazy deletion) is empty
		volatile int64_t& writesComplete;
		volatile SpringCleaningStats& springCleaningStats;
		volatile int64_t& diskBytesUsed;
		volatile int64_t& freeListPages;
		UID dbgid;
		vector<Reference<ReadCursor>>& readThreads;
		bool checkAllChecksumsOnOpen;
		bool checkIntegrityOnOpen;

		explicit Writer( std::string const& filename, bool isBtreeV2, bool checkAllChecksumsOnOpen, bool checkIntegrityOnOpen, volatile int64_t& writesComplete, volatile SpringCleaningStats& springCleaningStats, volatile int64_t& diskBytesUsed, volatile int64_t& freeListPages, UID dbgid, vector<Reference<ReadCursor>>* pReadThreads )
			: conn( filename, isBtreeV2, isBtreeV2 ),
			  commits(), setsThisCommit(),
			  freeTableEmpty(false),
			  writesComplete(writesComplete),
			  springCleaningStats(springCleaningStats),
			  diskBytesUsed(diskBytesUsed),
			  freeListPages(freeListPages),
			  cursor(NULL),
			  dbgid(dbgid),
			  readThreads(*pReadThreads),
			  checkAllChecksumsOnOpen(checkAllChecksumsOnOpen),
			  checkIntegrityOnOpen(checkIntegrityOnOpen)
		{
		}
		~Writer() {
			TraceEvent("KVWriterDestroying", dbgid);
			delete cursor;
			TraceEvent("KVWriterDestroyed", dbgid);
		}
		virtual void init() {
			if(checkAllChecksumsOnOpen) {
				if(conn.checkAllPageChecksums() != 0) {
					// It's not strictly necessary to discard the file immediately if a page checksum error is found
					// because most of the file could be valid and bad pages will be detected if they are read.
					// However, we shouldn't use the file unless we absolutely have to because some range(s) of keys
					// have effectively lost a replica.
					throw file_corrupt();
				}
			}
			conn.open(true);

			//If a wal file fails during the commit process before finishing a checkpoint, then it is possible that our wal file will be non-empty
			//when we reload it.  We execute a checkpoint here to remedy that situation.  This call must come before before creating a cursor because
			//it will fail if there are any outstanding transactions.
			fullCheckpoint();

			cursor = new Cursor(conn, true);

			if (checkIntegrityOnOpen || EXPENSIVE_VALIDATION) {
				if(conn.check(false) != 0) {
					// A corrupt btree structure must not be used.
					if (g_network->isSimulated() && (g_simulator.getCurrentProcess()->fault_injection_p1 || g_simulator.getCurrentProcess()->machine->machineProcess->fault_injection_p1 || g_simulator.getCurrentProcess()->rebooting)) {
						throw file_corrupt().asInjectedFault();
					} else {
						throw file_corrupt();
					}
				}
			}
		}

		struct InitAction : TypedAction<Writer, InitAction>, FastAllocated<InitAction> {
			ThreadReturnPromise<Void> result;
			virtual double getTimeEstimate() { return 0; }
		};
		void action(InitAction& a) {
			// init() has already been called
			a.result.send(Void());
		}

		struct SetAction : TypedAction<Writer, SetAction>, FastAllocated<SetAction> {
			KeyValue kv;
			SetAction( KeyValue kv ) : kv(kv) {}
			virtual double getTimeEstimate() { return SERVER_KNOBS->SET_TIME_ESTIMATE; }
		};
		void action(SetAction& a) {
			double s = now();
			checkFreePages();
			cursor->set(a.kv);
			++setsThisCommit;
			++writesComplete;
			if (g_network->isSimulated() && g_simulator.getCurrentProcess()->rebooting)
				TraceEvent("SetActionFinished", dbgid).detail("Elapsed", now()-s);
		}

		struct ClearAction : TypedAction<Writer, ClearAction>, FastAllocated<ClearAction> {
			KeyRange range;
			ClearAction( KeyRange range ) : range(range) {}
			virtual double getTimeEstimate() { return SERVER_KNOBS->CLEAR_TIME_ESTIMATE; }
		};
		void action(ClearAction& a) {
			double s = now();
			cursor->fastClear(a.range, freeTableEmpty);
			cursor->clear(a.range);  // TODO: at most one
			++writesComplete;
			if (g_network->isSimulated() && g_simulator.getCurrentProcess()->rebooting)
				TraceEvent("ClearActionFinished", dbgid).detail("Elapsed", now()-s);
		}

		struct CommitAction : TypedAction<Writer, CommitAction>, FastAllocated<CommitAction> {
			double issuedTime;
			ThreadReturnPromise<Void> result;
			CommitAction() : issuedTime(now()) {}
			virtual double getTimeEstimate() { return SERVER_KNOBS->COMMIT_TIME_ESTIMATE; }
		};
		void action(CommitAction& a) {
			double t1 = now();
			cursor->commit();
			delete cursor;
			cursor = NULL;

			double t2 = now();

			fullCheckpoint();

			double t3 = now();

			++commits;
			//if ( !(commits % 100) )
			//printf("dbf=%lld bytes, wal=%lld bytes\n", getFileSize((kv->filename+".fdb").c_str()), getFileSize((kv->filename+".fdb-wal").c_str()));

			a.result.send(Void());

			cursor = new Cursor(conn, true);
			checkFreePages();
			++writesComplete;
			if (t3-a.issuedTime > 10.0*deterministicRandom()->random01())
				TraceEvent("KVCommit10sSample", dbgid).detail("Queued", t1-a.issuedTime).detail("Commit", t2-t1).detail("Checkpoint", t3-t2);

			diskBytesUsed = waitForAndGet( conn.dbFile->size() ) + waitForAndGet( conn.walFile->size() );

			if (g_network->isSimulated() && g_simulator.getCurrentProcess()->rebooting)
				TraceEvent("CommitActionFinished", dbgid).detail("Elapsed", now()-t1);
		}

		//Checkpoints the database and resets the wal file back to the beginning
		void fullCheckpoint() {
			//A checkpoint cannot succeed while there is an outstanding transaction
			ASSERT(cursor == NULL);

			resetReaders();
			conn.checkpoint(false);

			resetReaders();
			conn.checkpoint(true);
		}

		void resetReaders() {
			for(int i=0; i<readThreads.size(); i++)
				readThreads[i].clear();
		}
		void checkFreePages() {
			int iterations = 0;

			int64_t freeListSize = freeListPages;
			while (!freeTableEmpty && freeListSize < SERVER_KNOBS->CHECK_FREE_PAGE_AMOUNT) {
				int deletedPages = cursor->lazyDelete(SERVER_KNOBS->CHECK_FREE_PAGE_AMOUNT);
				freeTableEmpty = (deletedPages != SERVER_KNOBS->CHECK_FREE_PAGE_AMOUNT);
				springCleaningStats.lazyDeletePages += deletedPages;
				++iterations;

				freeListSize = conn.freePages();
			}

			freeListPages = freeListSize;
			//if (iterations) printf("Lazy free: %d pages on freelist, %d iterations, freeTableEmpty=%d\n", freeListPages, iterationsi, freeTableEmpty);
		}

		struct SpringCleaningAction : TypedAction<Writer, SpringCleaningAction>, FastAllocated<SpringCleaningAction> {
			ThreadReturnPromise<SpringCleaningWorkPerformed> result;
			virtual double getTimeEstimate() { 
				return std::max(SERVER_KNOBS->SPRING_CLEANING_LAZY_DELETE_TIME_ESTIMATE, SERVER_KNOBS->SPRING_CLEANING_VACUUM_TIME_ESTIMATE);
			}
		};
		void action(SpringCleaningAction& a) {
			double s = now();
			double lazyDeleteEnd = now() + SERVER_KNOBS->SPRING_CLEANING_LAZY_DELETE_TIME_ESTIMATE;
			double vacuumEnd = now() + SERVER_KNOBS->SPRING_CLEANING_VACUUM_TIME_ESTIMATE;

			SpringCleaningWorkPerformed workPerformed;

			double lazyDeleteTime = 0;
			double vacuumTime = 0;

			const double lazyDeleteBatchProbability = 1.0 / (1 + SERVER_KNOBS->SPRING_CLEANING_VACUUMS_PER_LAZY_DELETE_PAGE * std::max(1, SERVER_KNOBS->SPRING_CLEANING_LAZY_DELETE_BATCH_SIZE));
			bool vacuumFinished = false;

			loop {
				double begin = now();
				bool canDelete = !freeTableEmpty 
				                 && (now() < lazyDeleteEnd || workPerformed.lazyDeletePages < SERVER_KNOBS->SPRING_CLEANING_MIN_LAZY_DELETE_PAGES) 
				                 && workPerformed.lazyDeletePages < SERVER_KNOBS->SPRING_CLEANING_MAX_LAZY_DELETE_PAGES;

				bool canVacuum = !vacuumFinished 
				                 && (now() < vacuumEnd || workPerformed.vacuumedPages < SERVER_KNOBS->SPRING_CLEANING_MIN_VACUUM_PAGES) 
				                 && workPerformed.vacuumedPages < SERVER_KNOBS->SPRING_CLEANING_MAX_VACUUM_PAGES;

				if(!canDelete && !canVacuum) {
					break;
				}

				if(canDelete && (!canVacuum || deterministicRandom()->random01() < lazyDeleteBatchProbability)) {
					TEST(canVacuum); // SQLite lazy deletion when vacuuming is active
					TEST(!canVacuum); // SQLite lazy deletion when vacuuming is inactive

					int pagesToDelete = std::max(1, std::min(SERVER_KNOBS->SPRING_CLEANING_LAZY_DELETE_BATCH_SIZE, SERVER_KNOBS->SPRING_CLEANING_MAX_LAZY_DELETE_PAGES - workPerformed.lazyDeletePages));
					int pagesDeleted = cursor->lazyDelete(pagesToDelete) ;
					freeTableEmpty = (pagesDeleted != pagesToDelete);
					workPerformed.lazyDeletePages += pagesDeleted;
					lazyDeleteTime += now() - begin;
				}
				else {
					ASSERT(canVacuum);
					TEST(canDelete); // SQLite vacuuming when lazy delete is active
					TEST(!canDelete); // SQLite vacuuming when lazy delete is inactive
					TEST(SERVER_KNOBS->SPRING_CLEANING_VACUUMS_PER_LAZY_DELETE_PAGE != 0); //SQLite vacuuming with nonzero vacuums_per_lazy_delete_page

					vacuumFinished = conn.vacuum();
					if(!vacuumFinished) {
						++workPerformed.vacuumedPages;
					}

					vacuumTime += now() - begin;
				}

				CoroThreadPool::waitFor(yield());
			}

			freeListPages = conn.freePages();

			TEST(workPerformed.lazyDeletePages > 0); // Pages lazily deleted
			TEST(workPerformed.vacuumedPages > 0); // Pages vacuumed
			TEST(vacuumTime > 0); // Time spent vacuuming
			TEST(lazyDeleteTime > 0); // Time spent lazy deleting

			++springCleaningStats.springCleaningCount;
			springCleaningStats.lazyDeletePages += workPerformed.lazyDeletePages;
			springCleaningStats.vacuumedPages += workPerformed.vacuumedPages;
			springCleaningStats.springCleaningTime += now() - s;
			springCleaningStats.vacuumTime += vacuumTime;
			springCleaningStats.lazyDeleteTime += lazyDeleteTime;

			a.result.send(workPerformed);
			++writesComplete;
			if (g_network->isSimulated() && g_simulator.getCurrentProcess()->rebooting)
				TraceEvent("SpringCleaningActionFinished", dbgid).detail("Elapsed", now()-s);
		}
	};


	ACTOR static Future<Void> logPeriodically( KeyValueStoreSQLite* self ) {
		state int64_t lastReadsComplete = 0;
		state int64_t lastWritesComplete = 0;
		loop {
			wait( delay(SERVER_KNOBS->DISK_METRIC_LOGGING_INTERVAL) );

			int64_t rc = self->readsComplete, wc = self->writesComplete;
			TraceEvent("DiskMetrics", self->logID)
				.detail("ReadOps", rc - lastReadsComplete)
				.detail("WriteOps", wc - lastWritesComplete)
				.detail("ReadQueue", self->readsRequested - rc)
				.detail("WriteQueue", self->writesRequested - wc)
				.detail("GlobalSQLiteMemoryHighWater", (int64_t)sqlite3_memory_highwater(1));

			TraceEvent("SpringCleaningMetrics", self->logID)
				.detail("SpringCleaningCount", self->springCleaningStats.springCleaningCount)
				.detail("LazyDeletePages", self->springCleaningStats.lazyDeletePages)
				.detail("VacuumedPages", self->springCleaningStats.vacuumedPages)
				.detail("SpringCleaningTime", self->springCleaningStats.springCleaningTime)
				.detail("LazyDeleteTime", self->springCleaningStats.lazyDeleteTime)
				.detail("VacuumTime", self->springCleaningStats.vacuumTime);

			lastReadsComplete = self->readsComplete;
			lastWritesComplete = self->writesComplete;
		}
	}

	ACTOR static Future<Void> stopOnError( KeyValueStoreSQLite* self ) {
		try {
			wait( self->readThreads->getError() || self->writeThread->getError() );
		} catch (Error& e) {
			if (e.code() == error_code_actor_cancelled)
				throw;
		}

		self->readThreads->stop();
		self->writeThread->stop();
		return Void();
	}

	ACTOR static void doClose( KeyValueStoreSQLite* self, bool deleteOnClose ) {
		state Error error = success();
		try {
			TraceEvent("KVClose", self->logID).detail("Del", deleteOnClose);
			self->starting.cancel();
			self->cleaning.cancel();
			self->logging.cancel();
			wait( self->readThreads->stop() && self->writeThread->stop() );
			if (deleteOnClose) {
				wait( IAsyncFileSystem::filesystem()->incrementalDeleteFile( self->filename, true ) );
				wait( IAsyncFileSystem::filesystem()->incrementalDeleteFile( self->filename + "-wal", false ) );
			}
		} catch (Error& e) {
			TraceEvent(SevError, "KVDoCloseError", self->logID)
				.error(e,true)
				.detail("Reason", e.code() == error_code_platform_error ? "could not delete database" : "unknown");
			error = e;
		}

		TraceEvent("KVClosed", self->logID);
		if( error.code() != error_code_actor_cancelled ) {
			self->stopped.send(Void());
			delete self;
		}
	}
};
IKeyValueStore* keyValueStoreSQLite( std::string const& filename, UID logID, KeyValueStoreType storeType, bool checkChecksums, bool checkIntegrity) {
	return new KeyValueStoreSQLite(filename, logID, storeType, checkChecksums, checkIntegrity);
}

ACTOR Future<Void> cleanPeriodically( KeyValueStoreSQLite* self ) {
	wait(delayJittered(SERVER_KNOBS->SPRING_CLEANING_NO_ACTION_INTERVAL));
	loop {
		KeyValueStoreSQLite::SpringCleaningWorkPerformed workPerformed = wait(self->doClean());

		double duration = std::numeric_limits<double>::max();
		if (workPerformed.lazyDeletePages >= SERVER_KNOBS->SPRING_CLEANING_LAZY_DELETE_BATCH_SIZE) {
			duration = std::min(duration, SERVER_KNOBS->SPRING_CLEANING_LAZY_DELETE_INTERVAL);
		}
		if (workPerformed.vacuumedPages > 0) {
			duration = std::min(duration, SERVER_KNOBS->SPRING_CLEANING_VACUUM_INTERVAL);
		}
		if (duration == std::numeric_limits<double>::max()) {
			duration = SERVER_KNOBS->SPRING_CLEANING_NO_ACTION_INTERVAL;
		}

		wait(delayJittered(duration));
	}
}

ACTOR static Future<Void> startReadThreadsWhen( KeyValueStoreSQLite* kv, Future<Void> onReady, UID id ) {
	wait(onReady);
	kv->startReadThreads();
	return Void();
}

sqlite3_vfs *vfsAsync();
static int vfs_registered = 0;

KeyValueStoreSQLite::KeyValueStoreSQLite(std::string const& filename, UID id, KeyValueStoreType storeType, bool checkChecksums, bool checkIntegrity)
	: type(storeType),
	  filename(filename),
	  logID(id),
	  readThreads(CoroThreadPool::createThreadPool()),
	  writeThread(CoroThreadPool::createThreadPool()),
	  readsRequested(0), writesRequested(0), writesComplete(0), diskBytesUsed(0), freeListPages(0)
{
	stopOnErr = stopOnError(this);

	#if SQLITE_THREADSAFE == 0
	ASSERT( writeThread->isCoro() );
	#endif

	if (!vfs_registered && writeThread->isCoro())
		if (sqlite3_vfs_register( vfsAsync(), true ) != SQLITE_OK)
			ASSERT(false);

	//The DB file should not already be open
	ASSERT(!vfsAsyncIsOpen(filename));

	readCursors.resize(64); //< number of read threads

	sqlite3_soft_heap_limit64( SERVER_KNOBS->SOFT_HEAP_LIMIT );  // SOMEDAY: Is this a performance issue?  Should we drop the cache sizes for individual threads?
	TaskPriority taskId = g_network->getCurrentTask();
	g_network->setCurrentTask(TaskPriority::DiskWrite);
	writeThread->addThread( new Writer(filename, type==KeyValueStoreType::SSD_BTREE_V2, checkChecksums, checkIntegrity, writesComplete, springCleaningStats, diskBytesUsed, freeListPages, id, &readCursors) );
	g_network->setCurrentTask(taskId);
	auto p = new Writer::InitAction();
	auto f = p->result.getFuture();
	writeThread->post( p );
	starting = startReadThreadsWhen( this, f, logID );
	cleaning = cleanPeriodically(this);
	logging = logPeriodically(this);
}
KeyValueStoreSQLite::~KeyValueStoreSQLite() {
	//printf("dbf=%lld bytes, wal=%lld bytes\n", getFileSize((filename+".fdb").c_str()), getFileSize((filename+".fdb-wal").c_str()));
}

StorageBytes KeyValueStoreSQLite::getStorageBytes() {
	int64_t free;
	int64_t total;

	g_network->getDiskBytes(parentDirectory(filename), free, total);

	return StorageBytes(free, total, diskBytesUsed, free + _PAGE_SIZE * freeListPages);
}

void KeyValueStoreSQLite::startReadThreads() {
	int nReadThreads = readCursors.size();
	TaskPriority taskId = g_network->getCurrentTask();
	g_network->setCurrentTask(TaskPriority::DiskRead);
	for(int i=0; i<nReadThreads; i++)
		readThreads->addThread( new Reader(filename, type==KeyValueStoreType::SSD_BTREE_V2, readsComplete, logID, &readCursors[i]) );
	g_network->setCurrentTask(taskId);
}

void KeyValueStoreSQLite::set( KeyValueRef keyValue, const Arena* arena ) {
	++writesRequested;
	writeThread->post( new Writer::SetAction(keyValue) );
}
void KeyValueStoreSQLite::clear( KeyRangeRef range, const Arena* arena ) {
	++writesRequested;
	writeThread->post( new Writer::ClearAction(range) );
}
Future<Void> KeyValueStoreSQLite::commit(bool sequential) {
	++writesRequested;
	auto p = new Writer::CommitAction;
	auto f = p->result.getFuture();
	writeThread->post(p);
	return f;
}
Future<Optional<Value>> KeyValueStoreSQLite::readValue( KeyRef key, Optional<UID> debugID ) {
	++readsRequested;
	auto p = new Reader::ReadValueAction(key, debugID);
	auto f = p->result.getFuture();
	readThreads->post(p);
	return f;
}
Future<Optional<Value>> KeyValueStoreSQLite::readValuePrefix( KeyRef key, int maxLength, Optional<UID> debugID ) {
	++readsRequested;
	auto p = new Reader::ReadValuePrefixAction(key, maxLength, debugID);
	auto f = p->result.getFuture();
	readThreads->post(p);
	return f;
}
Future<Standalone<VectorRef<KeyValueRef>>> KeyValueStoreSQLite::readRange( KeyRangeRef keys, int rowLimit, int byteLimit ) {
	++readsRequested;
	auto p = new Reader::ReadRangeAction(keys, rowLimit, byteLimit);
	auto f = p->result.getFuture();
	readThreads->post(p);
	return f;
}
Future<KeyValueStoreSQLite::SpringCleaningWorkPerformed> KeyValueStoreSQLite::doClean() {
	++writesRequested;
	auto p = new Writer::SpringCleaningAction;
	auto f = p->result.getFuture();
	writeThread->post(p);
	return f;
}

void createTemplateDatabase() {
	ASSERT( !vfs_registered );
	SQLiteDB db1("template.fdb", false, false);
	SQLiteDB db2("template.sqlite", true, true);
	db1.createFromScratch();
	db2.createFromScratch();
}

void GenerateIOLogChecksumFile(std::string filename) {
	if(!fileExists(filename)) {
		throw file_not_found();
	}

	FILE *f = fopen(filename.c_str(), "r");
	FILE *fout = fopen((filename + ".checksums").c_str(), "w");
	uint8_t buf[4096];
	unsigned int c = 0;
	while(fread(buf, 1, 4096, f) > 0)
		fprintf(fout, "%u %u\n", c++, hashlittle(buf, 4096, 0xab12fd93));
	fclose(f);
	fclose(fout);
}

// If integrity is true, a full btree integrity check is done.
// If integrity is false, only a scan of all pages to validate their checksums is done.
ACTOR Future<Void> KVFileCheck(std::string filename, bool integrity) {
	if(!fileExists(filename))
		throw file_not_found();

	StringRef kvFile(filename);
	KeyValueStoreType type = KeyValueStoreType::END;
	if(kvFile.endsWith(LiteralStringRef(".fdb")))
		type = KeyValueStoreType::SSD_BTREE_V1;
	else if(kvFile.endsWith(LiteralStringRef(".sqlite")))
		type = KeyValueStoreType::SSD_BTREE_V2;
	ASSERT(type != KeyValueStoreType::END);

	state IKeyValueStore* store = keyValueStoreSQLite(filename, UID(0, 0), type, !integrity, integrity);
	ASSERT(store != nullptr);

	// Wait for integry check to finish
	wait(success(store->readValue(StringRef())));

	if(store->getError().isError())
		wait(store->getError());
	Future<Void> c = store->onClosed();
	store->close();
	wait(c);

	return Void();
}