faster accesstime save restore (#439)

- Improvement: Reduce time a cache bucket is locked for write when flushing/garbage collecting
  - Change format for faster read/write and reduced size on disk
  - Don't lock index while writing manifest to disk
  - Skip garbage collect if we are currently in a Flush operation
  - BlockStore::Flush no longer terminates currently writing block
  - Garbage collect references to currently writing block but keep the block as new data may be added
  - Fix BlockStore::Prune used disk space calculation
  - Don't materialize data in filecas when we just need the size

4 files changed, 295 insertions, 155 deletions

diff --git a/src/zenserver/cache/cachedisklayer.cpp b/src/zenserver/cache/cachedisklayer.cpp
index 98a24116f..9883e2119 100644
--- a/src/zenserver/cache/cachedisklayer.cpp
+++ b/src/zenserver/cache/cachedisklayer.cpp
@@ -238,37 +238,90 @@ ZenCacheDiskLayer::CacheBucket::OpenOrCreate(std::filesystem::path BucketDir, bo
 		const auto _ =
 			MakeGuard([&] { ZEN_INFO("read store manifest '{}' in {}", ManifestPath, NiceTimeSpanMs(Timer.GetElapsedTimeMs())); });
 
-		for (CbFieldView Entry : Manifest["Timestamps"sv])
+		uint64_t Count = Manifest["Count"sv].AsUInt64(0);
+		if (Count != 0)
 		{
-			const CbObjectView Obj = Entry.AsObjectView();
-			const IoHash	   Key = Obj["Key"sv].AsHash();
-
-			if (auto It = m_Index.find(Key); It != m_Index.end())
+			std::vector<size_t> KeysIndexes;
+			KeysIndexes.reserve(Count);
+			CbArrayView KeyArray = Manifest["Keys"sv].AsArrayView();
+			for (CbFieldView& KeyView : KeyArray)
+			{
+				if (auto It = m_Index.find(KeyView.AsHash()); It != m_Index.end())
+				{
+					KeysIndexes.push_back(It.value());
+					continue;
+				}
+				KeysIndexes.push_back((uint64_t)-1);
+			}
+			size_t		KeyIndexOffset = 0;
+			CbArrayView TimeStampArray = Manifest["Timestamps"].AsArrayView();
+			for (CbFieldView& TimeStampView : TimeStampArray)
+			{
+				size_t KeyIndex = KeysIndexes[KeyIndexOffset++];
+				if (KeyIndex == (uint64_t)-1)
+				{
+					continue;
+				}
+				m_AccessTimes[KeyIndex] = TimeStampView.AsInt64();
+			}
+			KeyIndexOffset			 = 0;
+			CbArrayView RawHashArray = Manifest["RawHash"].AsArrayView();
+			for (CbFieldView& RawHashView : RawHashArray)
 			{
-				size_t EntryIndex = It.value();
-				ZEN_ASSERT_SLOW(EntryIndex < m_AccessTimes.size());
-				m_AccessTimes[EntryIndex] = Obj["LastAccess"sv].AsInt64();
+				size_t KeyIndex = KeysIndexes[KeyIndexOffset++];
+				if (KeyIndex == (uint64_t)-1)
+				{
+					continue;
+				}
+				m_Payloads[KeyIndex].RawHash = RawHashView.AsHash();
+			}
+			KeyIndexOffset			 = 0;
+			CbArrayView RawSizeArray = Manifest["RawSize"].AsArrayView();
+			for (CbFieldView& RawSizeView : RawSizeArray)
+			{
+				size_t KeyIndex = KeysIndexes[KeyIndexOffset++];
+				if (KeyIndex == (uint64_t)-1)
+				{
+					continue;
+				}
+				m_Payloads[KeyIndex].RawSize = RawSizeView.AsUInt64();
 			}
 		}
-		for (CbFieldView Entry : Manifest["RawInfo"sv])
+
+		////// Legacy format read
 		{
-			const CbObjectView Obj = Entry.AsObjectView();
-			const IoHash	   Key = Obj["Key"sv].AsHash();
-			if (auto It = m_Index.find(Key); It != m_Index.end())
+			for (CbFieldView Entry : Manifest["Timestamps"sv])
 			{
-				size_t EntryIndex = It.value();
-				ZEN_ASSERT_SLOW(EntryIndex < m_Payloads.size());
-
-				const IoHash   RawHash = Obj["RawHash"sv].AsHash();
-				const uint64_t RawSize = Obj["RawSize"sv].AsUInt64();
+				const CbObjectView Obj = Entry.AsObjectView();
+				const IoHash	   Key = Obj["Key"sv].AsHash();
 
-				if (RawHash == IoHash::Zero || RawSize == 0)
+				if (auto It = m_Index.find(Key); It != m_Index.end())
 				{
-					ZEN_SCOPED_ERROR("detected bad index entry in index - {}", EntryIndex);
+					size_t EntryIndex = It.value();
+					ZEN_ASSERT_SLOW(EntryIndex < m_AccessTimes.size());
+					m_AccessTimes[EntryIndex] = Obj["LastAccess"sv].AsInt64();
 				}
+			}
+			for (CbFieldView Entry : Manifest["RawInfo"sv])
+			{
+				const CbObjectView Obj = Entry.AsObjectView();
+				const IoHash	   Key = Obj["Key"sv].AsHash();
+				if (auto It = m_Index.find(Key); It != m_Index.end())
+				{
+					size_t EntryIndex = It.value();
+					ZEN_ASSERT_SLOW(EntryIndex < m_Payloads.size());
 
-				m_Payloads[EntryIndex].RawHash = RawHash;
-				m_Payloads[EntryIndex].RawSize = RawSize;
+					const IoHash   RawHash = Obj["RawHash"sv].AsHash();
+					const uint64_t RawSize = Obj["RawSize"sv].AsUInt64();
+
+					if (RawHash == IoHash::Zero || RawSize == 0)
+					{
+						ZEN_SCOPED_ERROR("detected bad index entry in index - {}", EntryIndex);
+					}
+
+					m_Payloads[EntryIndex].RawHash = RawHash;
+					m_Payloads[EntryIndex].RawSize = RawSize;
+				}
 			}
 		}
 	}
@@ -578,14 +631,17 @@ ZenCacheDiskLayer::CacheBucket::OpenLog(const bool IsNew)
 		auto BlockIt = BlockSizes.find(BlockLocation.BlockIndex);
 		if (BlockIt == BlockSizes.end())
 		{
-			ZEN_WARN("Unknown block {} for entry {}", BlockLocation.BlockIndex, Entry.first.ToHexString());
+			ZEN_WARN("Unknown block {} for entry {} in '{}'", BlockLocation.BlockIndex, Entry.first.ToHexString(), m_BucketDir);
 		}
 		else
 		{
 			uint64_t BlockSize = BlockIt->second;
 			if (BlockLocation.Offset + BlockLocation.Size > BlockSize)
 			{
-				ZEN_WARN("Range is outside of block {} for entry {}", BlockLocation.BlockIndex, Entry.first.ToHexString());
+				ZEN_WARN("Range is outside of block {} for entry {} in '{}'",
+						 BlockLocation.BlockIndex,
+						 Entry.first.ToHexString(),
+						 m_BucketDir);
 			}
 			else
 			{
@@ -783,21 +839,50 @@ void
 ZenCacheDiskLayer::CacheBucket::Flush()
 {
 	ZEN_TRACE_CPU("Z$::Disk::Bucket::Flush");
+	bool Expected = false;
+	if (m_IsFlushing || !m_IsFlushing.compare_exchange_strong(Expected, true))
+	{
+		return;
+	}
+	auto FlushingGuard = MakeGuard([&] { m_IsFlushing.store(false); });
 
-	m_BlockStore.Flush();
-
-	RwLock::SharedLockScope _(m_IndexLock);
+	m_BlockStore.Flush(/*ForceNewBlock*/ false);
 	m_SlogFile.Flush();
-	MakeIndexSnapshot();
-	SaveManifest();
+
+	std::vector<AccessTime>	   AccessTimes;
+	std::vector<BucketPayload> Payloads;
+	IndexMap				   Index;
+
+	{
+		RwLock::SharedLockScope IndexLock(m_IndexLock);
+		MakeIndexSnapshot();
+		Index		= m_Index;
+		Payloads	= m_Payloads;
+		AccessTimes = m_AccessTimes;
+	}
+	SaveManifest(MakeManifest(std::move(Index), std::move(AccessTimes), std::move(Payloads)));
 }
 
 void
-ZenCacheDiskLayer::CacheBucket::SaveManifest()
+ZenCacheDiskLayer::CacheBucket::SaveManifest(CbObject&& Manifest)
+{
+	ZEN_TRACE_CPU("Z$::Disk::Bucket::SaveManifest");
+	try
+	{
+		SaveCompactBinaryObject(m_BucketDir / "zen_manifest", Manifest);
+	}
+	catch (std::exception& Err)
+	{
+		ZEN_WARN("writing manifest FAILED, reason: '{}'", Err.what());
+	}
+}
+
+CbObject
+ZenCacheDiskLayer::CacheBucket::MakeManifest(IndexMap&& Index, std::vector<AccessTime>&& AccessTimes, std::vector<BucketPayload>&& Payloads)
 {
 	using namespace std::literals;
 
-	ZEN_TRACE_CPU("Z$::Disk::Bucket::SaveManifest");
+	ZEN_TRACE_CPU("Z$::Disk::Bucket::MakeManifest");
 
 	CbObjectWriter Writer;
 	Writer << "BucketId"sv << m_BucketId;
@@ -805,46 +890,40 @@ ZenCacheDiskLayer::CacheBucket::SaveManifest()
 
 	if (!m_Index.empty())
 	{
-		Writer.BeginArray("Timestamps"sv);
-		for (auto& Kv : m_Index)
+		Writer.AddInteger("Count"sv, gsl::narrow<std::uint64_t>(Index.size()));
+		Writer.BeginArray("Keys"sv);
+		for (auto& Kv : Index)
 		{
-			const IoHash& Key		 = Kv.first;
-			GcClock::Tick AccessTime = m_AccessTimes[Kv.second];
+			const IoHash& Key = Kv.first;
+			Writer.AddHash(Key);
+		}
+		Writer.EndArray();
 
-			Writer.BeginObject();
-			Writer << "Key"sv << Key;
-			Writer << "LastAccess"sv << AccessTime;
-			Writer.EndObject();
+		Writer.BeginArray("Timestamps"sv);
+		for (auto& Kv : Index)
+		{
+			GcClock::Tick AccessTime = AccessTimes[Kv.second];
+			Writer.AddInteger(AccessTime);
 		}
 		Writer.EndArray();
 
-		Writer.BeginArray("RawInfo"sv);
+		Writer.BeginArray("RawHash"sv);
+		for (auto& Kv : Index)
 		{
-			for (auto& Kv : m_Index)
-			{
-				const IoHash&		 Key	 = Kv.first;
-				const BucketPayload& Payload = m_Payloads[Kv.second];
-				if (Payload.RawHash != IoHash::Zero)
-				{
-					Writer.BeginObject();
-					Writer << "Key"sv << Key;
-					Writer << "RawHash"sv << Payload.RawHash;
-					Writer << "RawSize"sv << Payload.RawSize;
-					Writer.EndObject();
-				}
-			}
+			const BucketPayload& Payload = Payloads[Kv.second];
+			Writer.AddHash(Payload.RawHash);
 		}
 		Writer.EndArray();
-	}
 
-	try
-	{
-		SaveCompactBinaryObject(m_BucketDir / "zen_manifest", Writer.Save());
-	}
-	catch (std::exception& Err)
-	{
-		ZEN_WARN("writing manifest FAILED, reason: '{}'", Err.what());
+		Writer.BeginArray("RawSize"sv);
+		for (auto& Kv : Index)
+		{
+			const BucketPayload& Payload = Payloads[Kv.second];
+			Writer.AddInteger(Payload.RawSize);
+		}
+		Writer.EndArray();
 	}
+	return Writer.Save();
 }
 
 IoHash
@@ -1200,7 +1279,10 @@ ZenCacheDiskLayer::CacheBucket::GatherReferences(GcContext& GcCtx)
 	ExpiredKeys.reserve(1024);
 
 	std::vector<IoHash> Cids;
-	Cids.reserve(1024);
+	if (!GcCtx.SkipCid())
+	{
+		Cids.reserve(1024);
+	}
 
 	for (const auto& Entry : Index)
 	{
@@ -1298,8 +1380,25 @@ ZenCacheDiskLayer::CacheBucket::CollectGarbage(GcContext& GcCtx)
 			MovedCount,
 			TotalChunkCount,
 			NiceBytes(OldTotalSize));
-		RwLock::SharedLockScope _(m_IndexLock);
-		SaveManifest();
+
+		bool Expected = false;
+		if (m_IsFlushing || !m_IsFlushing.compare_exchange_strong(Expected, true))
+		{
+			return;
+		}
+		auto FlushingGuard = MakeGuard([&] { m_IsFlushing.store(false); });
+
+		std::vector<AccessTime>	   AccessTimes;
+		std::vector<BucketPayload> Payloads;
+		IndexMap				   Index;
+		{
+			RwLock::SharedLockScope IndexLock(m_IndexLock);
+			MakeIndexSnapshot();
+			Index		= m_Index;
+			Payloads	= m_Payloads;
+			AccessTimes = m_AccessTimes;
+		}
+		SaveManifest(MakeManifest(std::move(Index), std::move(AccessTimes), std::move(Payloads)));
 	});
 
 	m_SlogFile.Flush();
@@ -1360,48 +1459,63 @@ ZenCacheDiskLayer::CacheBucket::CollectGarbage(GcContext& GcCtx)
 	IndexMap						 Index;
 	BlockStore::ReclaimSnapshotState BlockStoreState;
 	{
-		ZEN_TRACE_CPU("Z$::Disk::Bucket::CollectGarbage::State");
-
-		RwLock::SharedLockScope __(m_IndexLock);
-		Stopwatch				Timer;
-		const auto				____ = MakeGuard([&] {
-			 uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
-			 WriteBlockTimeUs += ElapsedUs;
-			 WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
-		 });
-		if (m_Index.empty())
+		bool Expected = false;
+		if (m_IsFlushing || !m_IsFlushing.compare_exchange_strong(Expected, true))
 		{
-			ZEN_DEBUG("garbage collect SKIPPED, for '{}', container is empty", m_BucketDir);
+			ZEN_DEBUG("garbage collect SKIPPED, for '{}', container is currently flushing", m_BucketDir);
 			return;
 		}
-		BlockStoreState = m_BlockStore.GetReclaimSnapshotState();
-
-		SaveManifest();
-		Index = m_Index;
+		auto FlushingGuard = MakeGuard([&] { m_IsFlushing.store(false); });
 
-		for (const IoHash& Key : DeleteCacheKeys)
+		std::vector<AccessTime>	   AccessTimes;
+		std::vector<BucketPayload> Payloads;
 		{
-			if (auto It = Index.find(Key); It != Index.end())
+			ZEN_TRACE_CPU("Z$::Disk::Bucket::CollectGarbage::State");
+			RwLock::SharedLockScope IndexLock(m_IndexLock);
+
+			Stopwatch  Timer;
+			const auto ____ = MakeGuard([&] {
+				uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
+				WriteBlockTimeUs += ElapsedUs;
+				WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
+			});
+			if (m_Index.empty())
 			{
-				const BucketPayload& Payload = m_Payloads[It->second];
-				DiskIndexEntry		 Entry	 = {.Key = It->first, .Location = Payload.Location};
-				if (Entry.Location.Flags & DiskLocation::kStandaloneFile)
+				ZEN_DEBUG("garbage collect SKIPPED, for '{}', container is empty", m_BucketDir);
+				return;
+			}
+
+			BlockStoreState = m_BlockStore.GetReclaimSnapshotState();
+
+			Payloads	= m_Payloads;
+			AccessTimes = m_AccessTimes;
+			Index		= m_Index;
+
+			for (const IoHash& Key : DeleteCacheKeys)
+			{
+				if (auto It = Index.find(Key); It != Index.end())
 				{
-					Entry.Location.Flags |= DiskLocation::kTombStone;
-					ExpiredStandaloneEntries.push_back(Entry);
+					const BucketPayload& Payload = m_Payloads[It->second];
+					DiskIndexEntry		 Entry	 = {.Key = It->first, .Location = Payload.Location};
+					if (Entry.Location.Flags & DiskLocation::kStandaloneFile)
+					{
+						Entry.Location.Flags |= DiskLocation::kTombStone;
+						ExpiredStandaloneEntries.push_back(Entry);
+					}
 				}
 			}
-		}
-		if (GcCtx.IsDeletionMode())
-		{
-			for (const auto& Entry : ExpiredStandaloneEntries)
+			if (GcCtx.IsDeletionMode())
 			{
-				m_Index.erase(Entry.Key);
-				m_TotalStandaloneSize.fetch_sub(Entry.Location.Size(), std::memory_order::relaxed);
-				DeletedChunks.insert(Entry.Key);
+				for (const auto& Entry : ExpiredStandaloneEntries)
+				{
+					m_Index.erase(Entry.Key);
+					m_TotalStandaloneSize.fetch_sub(Entry.Location.Size(), std::memory_order::relaxed);
+					DeletedChunks.insert(Entry.Key);
+				}
+				m_SlogFile.Append(ExpiredStandaloneEntries);
 			}
-			m_SlogFile.Append(ExpiredStandaloneEntries);
 		}
+		SaveManifest(MakeManifest(std::move(Index), std::move(AccessTimes), std::move(Payloads)));
 	}
 
 	if (GcCtx.IsDeletionMode())
diff --git a/src/zenserver/cache/cachedisklayer.h b/src/zenserver/cache/cachedisklayer.h
index 80c643afa..c4bedfee8 100644
--- a/src/zenserver/cache/cachedisklayer.h
+++ b/src/zenserver/cache/cachedisklayer.h
@@ -188,6 +188,7 @@ private:
 		BlockStore			  m_BlockStore;
 		Oid					  m_BucketId;
 		uint64_t			  m_LargeObjectThreshold = 128 * 1024;
+		std::atomic_bool	  m_IsFlushing{};
 
 		// These files are used to manage storage of small objects for this bucket
 
@@ -221,16 +222,17 @@ private:
 
 		std::atomic_uint64_t m_TotalStandaloneSize{};
 
-		void							BuildPath(PathBuilderBase& Path, const IoHash& HashKey) const;
-		void							PutStandaloneCacheValue(const IoHash& HashKey, const ZenCacheValue& Value);
-		IoBuffer						GetStandaloneCacheValue(const DiskLocation& Loc, const IoHash& HashKey) const;
-		void							PutInlineCacheValue(const IoHash& HashKey, const ZenCacheValue& Value);
-		IoBuffer						GetInlineCacheValue(const DiskLocation& Loc) const;
-		void							MakeIndexSnapshot();
-		uint64_t						ReadIndexFile(const std::filesystem::path& IndexPath, uint32_t& OutVersion);
-		uint64_t						ReadLog(const std::filesystem::path& LogPath, uint64_t LogPosition);
-		void							OpenLog(const bool IsNew);
-		void							SaveManifest();
+		void	 BuildPath(PathBuilderBase& Path, const IoHash& HashKey) const;
+		void	 PutStandaloneCacheValue(const IoHash& HashKey, const ZenCacheValue& Value);
+		IoBuffer GetStandaloneCacheValue(const DiskLocation& Loc, const IoHash& HashKey) const;
+		void	 PutInlineCacheValue(const IoHash& HashKey, const ZenCacheValue& Value);
+		IoBuffer GetInlineCacheValue(const DiskLocation& Loc) const;
+		void	 MakeIndexSnapshot();
+		uint64_t ReadIndexFile(const std::filesystem::path& IndexPath, uint32_t& OutVersion);
+		uint64_t ReadLog(const std::filesystem::path& LogPath, uint64_t LogPosition);
+		void	 OpenLog(const bool IsNew);
+		CbObject MakeManifest(IndexMap&& Index, std::vector<AccessTime>&& AccessTimes, std::vector<BucketPayload>&& Payloads);
+		void	 SaveManifest(CbObject&& Manifest);
 		CacheValueDetails::ValueDetails GetValueDetails(const IoHash& Key, size_t Index) const;
 		// These locks are here to avoid contention on file creation, therefore it's sufficient
 		// that we take the same lock for the same hash
diff --git a/src/zenserver/cache/structuredcachestore.cpp b/src/zenserver/cache/structuredcachestore.cpp
index 0a2947b16..1b6eeca3a 100644
--- a/src/zenserver/cache/structuredcachestore.cpp
+++ b/src/zenserver/cache/structuredcachestore.cpp
@@ -1030,46 +1030,50 @@ TEST_CASE("z$.gc")
 	{
 		ScopedTemporaryDirectory TempDir;
 		GcManager				 Gc;
-		ZenCacheNamespace		 Zcs(Gc, *JobQueue, TempDir.Path() / "cache");
-		const auto				 Bucket = "rightintwo"sv;
-
-		std::vector<IoHash> Keys{CreateKey(1), CreateKey(2), CreateKey(3)};
-
-		for (const auto& Key : Keys)
 		{
-			IoBuffer Value = testutils::CreateBinaryCacheValue(128);
-			Zcs.Put(Bucket, Key, {.Value = Value});
-		}
-
-		{
-			GcContext GcCtx(GcClock::Now() - std::chrono::hours(2), GcClock::Now() - std::chrono::hours(2));
-			GcCtx.CollectSmallObjects(true);
+			ZenCacheNamespace Zcs(Gc, *JobQueue, TempDir.Path() / "cache");
+			const auto		  Bucket = "rightintwo"sv;
 
-			Gc.CollectGarbage(GcCtx);
+			std::vector<IoHash> Keys{CreateKey(1), CreateKey(2), CreateKey(3)};
 
 			for (const auto& Key : Keys)
 			{
-				ZenCacheValue CacheValue;
-				const bool	  Exists = Zcs.Get(Bucket, Key, CacheValue);
-				CHECK(Exists);
+				IoBuffer Value = testutils::CreateBinaryCacheValue(128);
+				Zcs.Put(Bucket, Key, {.Value = Value});
 			}
-		}
 
-		// Move forward in time and collect again
-		{
-			GcContext GcCtx(GcClock::Now() + std::chrono::minutes(2), GcClock::Now() + std::chrono::minutes(2));
-			GcCtx.CollectSmallObjects(true);
+			{
+				GcContext GcCtx(GcClock::Now() - std::chrono::hours(2), GcClock::Now() - std::chrono::hours(2));
+				GcCtx.CollectSmallObjects(true);
 
-			Zcs.Flush();
-			Gc.CollectGarbage(GcCtx);
+				Gc.CollectGarbage(GcCtx);
 
-			for (const auto& Key : Keys)
-			{
-				ZenCacheValue CacheValue;
-				const bool	  Exists = Zcs.Get(Bucket, Key, CacheValue);
-				CHECK(!Exists);
+				for (const auto& Key : Keys)
+				{
+					ZenCacheValue CacheValue;
+					const bool	  Exists = Zcs.Get(Bucket, Key, CacheValue);
+					CHECK(Exists);
+				}
 			}
 
+			// Move forward in time and collect again
+			{
+				GcContext GcCtx(GcClock::Now() + std::chrono::minutes(2), GcClock::Now() + std::chrono::minutes(2));
+				GcCtx.CollectSmallObjects(true);
+
+				Zcs.Flush();
+				Gc.CollectGarbage(GcCtx);
+
+				for (const auto& Key : Keys)
+				{
+					ZenCacheValue CacheValue;
+					const bool	  Exists = Zcs.Get(Bucket, Key, CacheValue);
+					CHECK(!Exists);
+				}
+			}
+		}
+		{
+			ZenCacheNamespace Zcs(Gc, *JobQueue, TempDir.Path() / "cache");
 			CHECK_EQ(0, Zcs.StorageSize().DiskSize);
 		}
 	}
diff --git a/src/zenserver/projectstore/projectstore.cpp b/src/zenserver/projectstore/projectstore.cpp
index 4ddbdded7..4402e4486 100644
--- a/src/zenserver/projectstore/projectstore.cpp
+++ b/src/zenserver/projectstore/projectstore.cpp
@@ -1239,15 +1239,37 @@ ProjectStore::Project::ReadAccessTimes()
 
 	if (ValidationError == CbValidateError::None)
 	{
-		CbObject	Reader			= LoadCompactBinaryObject(Obj);
-		CbArrayView LastAccessTimes = Reader["lastaccess"sv].AsArrayView();
+		CbObject Reader = LoadCompactBinaryObject(Obj);
 
-		for (CbFieldView& Entry : LastAccessTimes)
+		uint64_t Count = Reader["count"sv].AsUInt64(0);
+		if (Count > 0)
 		{
-			CbObjectView	 AccessTime = Entry.AsObjectView();
-			std::string_view Id			= AccessTime["id"sv].AsString();
-			GcClock::Tick	 AccessTick = AccessTime["tick"sv].AsUInt64();
-			m_LastAccessTimes.insert_or_assign(std::string(Id), AccessTick);
+			std::vector<uint64_t> Ticks;
+			Ticks.reserve(Count);
+			CbArrayView TicksArray = Reader["ticks"sv].AsArrayView();
+			for (CbFieldView& TickView : TicksArray)
+			{
+				Ticks.emplace_back(TickView.AsUInt64());
+			}
+			CbArrayView IdArray = Reader["ids"sv].AsArrayView();
+			uint64_t	Index	= 0;
+			for (CbFieldView& IdView : IdArray)
+			{
+				std::string_view Id = IdView.AsString();
+				m_LastAccessTimes.insert_or_assign(std::string(Id), Ticks[Index++]);
+			}
+		}
+
+		////// Legacy format read
+		{
+			CbArrayView LastAccessTimes = Reader["lastaccess"sv].AsArrayView();
+			for (CbFieldView& Entry : LastAccessTimes)
+			{
+				CbObjectView	 AccessTime = Entry.AsObjectView();
+				std::string_view Id			= AccessTime["id"sv].AsString();
+				GcClock::Tick	 AccessTick = AccessTime["tick"sv].AsUInt64();
+				m_LastAccessTimes.insert_or_assign(std::string(Id), AccessTick);
+			}
 		}
 	}
 	else
@@ -1261,26 +1283,27 @@ ProjectStore::Project::WriteAccessTimes()
 {
 	using namespace std::literals;
 
-	RwLock::ExclusiveLockScope _(m_ProjectLock);
+	CbObjectWriter Writer;
 
-	BinaryWriter Mem;
+	Writer.AddInteger("count", gsl::narrow<uint64_t>(m_LastAccessTimes.size()));
+	Writer.BeginArray("ids");
 
-	CbObjectWriter Writer;
-	Writer.BeginArray("lastaccess");
 	{
+		RwLock::SharedLockScope _(m_ProjectLock);
 		for (const auto& It : m_LastAccessTimes)
 		{
-			Writer.BeginObject();
-			{
-				Writer << "id"sv << It.first;
-				Writer << "tick"sv << gsl::narrow<uint64_t>(It.second);
-			}
-			Writer.EndObject();
+			Writer << It.first;
 		}
+		Writer.EndArray();
+		Writer.BeginArray("ticks");
+		for (const auto& It : m_LastAccessTimes)
+		{
+			Writer << gsl::narrow<uint64_t>(It.second);
+		}
+		Writer.EndArray();
 	}
-	Writer.EndArray();
 
-	Writer.Save(Mem);
+	CbObject Data = Writer.Save();
 
 	try
 	{
@@ -1290,10 +1313,7 @@ ProjectStore::Project::WriteAccessTimes()
 
 		ZEN_INFO("persisting access times for project '{}' to {}", Identifier, ProjectAccessTimesFilePath);
 
-		BasicFile Blob;
-		Blob.Open(ProjectAccessTimesFilePath, BasicFile::Mode::kTruncate);
-		Blob.Write(Mem.Data(), Mem.Size(), 0);
-		Blob.Flush();
+		WriteFile(ProjectAccessTimesFilePath, Data.GetBuffer().AsIoBuffer());
 	}
 	catch (std::exception& Err)
 	{