Make sure we monitor for new project, oplogs, namespaces and buckets during GCv2 (#93)

- Bugfix: Make sure we monitor and include new project/oplogs created during GCv2
- Bugfix: Make sure we monitor and include new namespaces/cache buckets created during GCv2

6 files changed, 571 insertions, 175 deletions

diff --git a/src/zenstore/cache/cachedisklayer.cpp b/src/zenstore/cache/cachedisklayer.cpp
index 9dd2e4a67..f865e1c3c 100644
--- a/src/zenstore/cache/cachedisklayer.cpp
+++ b/src/zenstore/cache/cachedisklayer.cpp
@@ -3383,6 +3383,101 @@ ZenCacheDiskLayer::CacheBucket::RemoveExpiredData(GcCtx& Ctx, GcStats& Stats)
 	return new DiskBucketStoreCompactor(*this, std::move(ExpiredStandaloneKeys));
 }
 
+bool
+ZenCacheDiskLayer::CacheBucket::GetReferencesLocked(GcCtx& Ctx, std::vector<IoHash>& OutReferences)
+{
+	auto GetAttachments = [&](const void* CbObjectData) {
+		CbObjectView Obj(CbObjectData);
+		Obj.IterateAttachments([&](CbFieldView Field) { OutReferences.emplace_back(Field.AsAttachment()); });
+	};
+
+	std::vector<std::pair<IoHash, DiskLocation>> StandaloneKeys;
+	{
+		std::vector<IoHash>					  InlineKeys;
+		std::vector<BlockStoreLocation>		  InlineLocations;
+		std::vector<std::vector<std::size_t>> InlineBlockChunkIndexes;
+
+		{
+			std::unordered_map<uint32_t, std::size_t> BlockIndexToChunkIndexes;
+
+			for (const auto& Entry : m_Index)
+			{
+				if (Ctx.IsCancelledFlag.load())
+				{
+					return false;
+				}
+
+				PayloadIndex		 EntryIndex = Entry.second;
+				const BucketPayload& Payload	= m_Payloads[EntryIndex];
+				const DiskLocation&	 Loc		= Payload.Location;
+
+				if (!Loc.IsFlagSet(DiskLocation::kStructured))
+				{
+					continue;
+				}
+				const IoHash& Key = Entry.first;
+				if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
+				{
+					StandaloneKeys.push_back(std::make_pair(Key, Loc));
+					continue;
+				}
+
+				BlockStoreLocation ChunkLocation = Loc.GetBlockLocation(m_Configuration.PayloadAlignment);
+				size_t			   ChunkIndex	 = InlineLocations.size();
+				InlineLocations.push_back(ChunkLocation);
+				InlineKeys.push_back(Key);
+				if (auto It = BlockIndexToChunkIndexes.find(ChunkLocation.BlockIndex); It != BlockIndexToChunkIndexes.end())
+				{
+					InlineBlockChunkIndexes[It->second].push_back(ChunkIndex);
+				}
+				else
+				{
+					BlockIndexToChunkIndexes.insert_or_assign(ChunkLocation.BlockIndex, InlineBlockChunkIndexes.size());
+					InlineBlockChunkIndexes.emplace_back(std::vector<size_t>{ChunkIndex});
+				}
+			}
+		}
+
+		for (std::vector<std::size_t> ChunkIndexes : InlineBlockChunkIndexes)
+		{
+			ZEN_ASSERT(!ChunkIndexes.empty());
+
+			bool Continue = m_BlockStore.IterateBlock(
+				InlineLocations,
+				ChunkIndexes,
+				[&](size_t ChunkIndex, const void* Data, uint64_t Size) {
+					ZEN_UNUSED(ChunkIndex, Size);
+					GetAttachments(Data);
+					return !Ctx.IsCancelledFlag.load();
+				},
+				[&](size_t ChunkIndex, BlockStoreFile& File, uint64_t Offset, uint64_t Size) {
+					ZEN_UNUSED(ChunkIndex);
+					GetAttachments(File.GetChunk(Offset, Size).GetData());
+					return !Ctx.IsCancelledFlag.load();
+				});
+
+			if (!Continue && Ctx.IsCancelledFlag.load())
+			{
+				return false;
+			}
+		}
+	}
+	for (const auto& It : StandaloneKeys)
+	{
+		if (Ctx.IsCancelledFlag.load())
+		{
+			return false;
+		}
+
+		IoBuffer Buffer = GetStandaloneCacheValue(It.second, It.first);
+		if (Buffer)
+		{
+			GetAttachments(Buffer.GetData());
+		}
+	}
+	return true;
+}
+
 class DiskBucketReferenceChecker : public GcReferenceChecker
 {
 	using PayloadIndex	= ZenCacheDiskLayer::CacheBucket::PayloadIndex;
@@ -3396,7 +3491,6 @@ public:
 	{
 		try
 		{
-			m_IndexLock.reset();
 			m_CacheBucket.m_IndexLock.WithExclusiveLock([&]() { m_CacheBucket.m_TrackedReferences.reset(); });
 		}
 		catch (const std::exception& Ex)
@@ -3419,114 +3513,25 @@ public:
 			}
 			ZEN_INFO("GCV2: cachebucket [PRECACHE] '{}': found {} references in {}",
 					 m_CacheBucket.m_BucketDir,
-					 m_PrecachedReferences.size(),
+					 m_References.size(),
 					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
 		});
 
-		auto GetAttachments = [&](const void* CbObjectData) {
-			CbObjectView Obj(CbObjectData);
-			Obj.IterateAttachments([&](CbFieldView Field) { m_PrecachedReferences.emplace_back(Field.AsAttachment()); });
-		};
-
-		// Refresh cache
-		{
-			m_CacheBucket.m_IndexLock.WithExclusiveLock([&]() { m_CacheBucket.m_TrackedReferences = std::make_unique<HashSet>(); });
+		m_CacheBucket.m_IndexLock.WithExclusiveLock([&]() { m_CacheBucket.m_TrackedReferences = std::make_unique<HashSet>(); });
 
-			std::vector<std::pair<IoHash, DiskLocation>> StandaloneKeys;
-			{
-				std::vector<IoHash>					  InlineKeys;
-				std::vector<BlockStoreLocation>		  InlineLocations;
-				std::vector<std::vector<std::size_t>> InlineBlockChunkIndexes;
-
-				{
-					std::unordered_map<uint32_t, std::size_t> BlockIndexToChunkIndexes;
-
-					RwLock::SharedLockScope IndexLock(m_CacheBucket.m_IndexLock);
-					for (const auto& Entry : m_CacheBucket.m_Index)
-					{
-						if (Ctx.IsCancelledFlag.load())
-						{
-							IndexLock.ReleaseNow();
-							m_CacheBucket.m_IndexLock.WithExclusiveLock([&]() { m_CacheBucket.m_TrackedReferences.reset(); });
-							return;
-						}
-
-						PayloadIndex		 EntryIndex = Entry.second;
-						const BucketPayload& Payload	= m_CacheBucket.m_Payloads[EntryIndex];
-						const DiskLocation&	 Loc		= Payload.Location;
-
-						if (!Loc.IsFlagSet(DiskLocation::kStructured))
-						{
-							continue;
-						}
-						const IoHash& Key = Entry.first;
-						if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
-						{
-							StandaloneKeys.push_back(std::make_pair(Key, Loc));
-							continue;
-						}
-
-						BlockStoreLocation ChunkLocation = Loc.GetBlockLocation(m_CacheBucket.m_Configuration.PayloadAlignment);
-						size_t			   ChunkIndex	 = InlineLocations.size();
-						InlineLocations.push_back(ChunkLocation);
-						InlineKeys.push_back(Key);
-						if (auto It = BlockIndexToChunkIndexes.find(ChunkLocation.BlockIndex); It != BlockIndexToChunkIndexes.end())
-						{
-							InlineBlockChunkIndexes[It->second].push_back(ChunkIndex);
-						}
-						else
-						{
-							BlockIndexToChunkIndexes.insert_or_assign(ChunkLocation.BlockIndex, InlineBlockChunkIndexes.size());
-							InlineBlockChunkIndexes.emplace_back(std::vector<size_t>{ChunkIndex});
-						}
-					}
-				}
-
-				for (std::vector<std::size_t> ChunkIndexes : InlineBlockChunkIndexes)
-				{
-					ZEN_ASSERT(!ChunkIndexes.empty());
-
-					bool Continue = m_CacheBucket.m_BlockStore.IterateBlock(
-						InlineLocations,
-						ChunkIndexes,
-						[&](size_t ChunkIndex, const void* Data, uint64_t Size) {
-							ZEN_UNUSED(ChunkIndex, Size);
-							GetAttachments(Data);
-							return !Ctx.IsCancelledFlag.load();
-						},
-						[&](size_t ChunkIndex, BlockStoreFile& File, uint64_t Offset, uint64_t Size) {
-							ZEN_UNUSED(ChunkIndex);
-							GetAttachments(File.GetChunk(Offset, Size).GetData());
-							return !Ctx.IsCancelledFlag.load();
-						});
-
-					if (!Continue && Ctx.IsCancelledFlag.load())
-					{
-						m_CacheBucket.m_IndexLock.WithExclusiveLock([&]() { m_CacheBucket.m_TrackedReferences.reset(); });
-						return;
-					}
-				}
-			}
-			for (const auto& It : StandaloneKeys)
-			{
-				if (Ctx.IsCancelledFlag.load())
-				{
-					m_CacheBucket.m_IndexLock.WithExclusiveLock([&]() { m_CacheBucket.m_TrackedReferences.reset(); });
-					return;
-				}
+		RwLock::SharedLockScope IndexLock(m_CacheBucket.m_IndexLock);
+		bool					Continue = m_CacheBucket.GetReferencesLocked(Ctx, m_References);
+		IndexLock.ReleaseNow();
 
-				IoBuffer Buffer = m_CacheBucket.GetStandaloneCacheValue(It.second, It.first);
-				if (Buffer)
-				{
-					GetAttachments(Buffer.GetData());
-				}
-			}
+		if (!Continue)
+		{
+			m_CacheBucket.m_IndexLock.WithExclusiveLock([&]() { m_CacheBucket.m_TrackedReferences.reset(); });
 		}
 	}
 
-	virtual void LockState(GcCtx& Ctx) override
+	virtual void UpdateLockedState(GcCtx& Ctx) override
 	{
-		ZEN_TRACE_CPU("Z$::Bucket::LockState");
+		ZEN_TRACE_CPU("Z$::Bucket::UpdateLockedState");
 
 		Stopwatch  Timer;
 		const auto _ = MakeGuard([&] {
@@ -3536,32 +3541,28 @@ public:
 			}
 			ZEN_INFO("GCV2: cachebucket [LOCKSTATE] '{}': found {} references in {}",
 					 m_CacheBucket.m_BucketDir,
-					 m_PrecachedReferences.size() + m_UncachedReferences.size(),
+					 m_References.size(),
 					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
 		});
 
-		m_IndexLock = std::make_unique<RwLock::SharedLockScope>(m_CacheBucket.m_IndexLock);
 		if (Ctx.IsCancelledFlag.load())
 		{
-			m_UncachedReferences = {};
-			m_IndexLock.reset();
-			m_CacheBucket.m_IndexLock.WithExclusiveLock([&]() { m_CacheBucket.m_TrackedReferences.reset(); });
+			m_References = {};
+			m_CacheBucket.m_TrackedReferences.reset();
 			return;
 		}
 
 		ZEN_ASSERT(m_CacheBucket.m_TrackedReferences);
 
 		HashSet& AddedReferences(*m_CacheBucket.m_TrackedReferences);
-		m_UncachedReferences.reserve(AddedReferences.size());
-		m_UncachedReferences.insert(m_UncachedReferences.end(), AddedReferences.begin(), AddedReferences.end());
+		m_References.reserve(m_References.size() + AddedReferences.size());
+		m_References.insert(m_References.end(), AddedReferences.begin(), AddedReferences.end());
 		AddedReferences = {};
 	}
 
 	virtual void RemoveUsedReferencesFromSet(GcCtx& Ctx, HashSet& IoCids) override
 	{
 		ZEN_TRACE_CPU("Z$::Bucket::RemoveUsedReferencesFromSet");
-
-		ZEN_ASSERT(m_IndexLock);
 		size_t	   InitialCount = IoCids.size();
 		Stopwatch  Timer;
 		const auto _ = MakeGuard([&] {
@@ -3576,18 +3577,7 @@ public:
 					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
 		});
 
-		for (const IoHash& ReferenceHash : m_PrecachedReferences)
-		{
-			if (IoCids.erase(ReferenceHash) == 1)
-			{
-				if (IoCids.empty())
-				{
-					return;
-				}
-			}
-		}
-
-		for (const IoHash& ReferenceHash : m_UncachedReferences)
+		for (const IoHash& ReferenceHash : m_References)
 		{
 			if (IoCids.erase(ReferenceHash) == 1)
 			{
@@ -3598,10 +3588,8 @@ public:
 			}
 		}
 	}
-	CacheBucket&							 m_CacheBucket;
-	std::unique_ptr<RwLock::SharedLockScope> m_IndexLock;
-	std::vector<IoHash>						 m_PrecachedReferences;
-	std::vector<IoHash>						 m_UncachedReferences;
+	CacheBucket&		m_CacheBucket;
+	std::vector<IoHash> m_References;
 };
 
 std::vector<GcReferenceChecker*>
@@ -3673,6 +3661,12 @@ ZenCacheDiskLayer::CacheBucket::CompactState(RwLock::ExclusiveLockScope&,
 	Reset(m_FreeMemCachedPayloads);
 }
 
+RwLock::SharedLockScope
+ZenCacheDiskLayer::CacheBucket::GetGcReferencerLock()
+{
+	return RwLock::SharedLockScope(m_IndexLock);
+}
+
 #if ZEN_WITH_TESTS
 void
 ZenCacheDiskLayer::CacheBucket::SetAccessTime(const IoHash& HashKey, GcClock::TimePoint Time)
@@ -3763,7 +3757,12 @@ ZenCacheDiskLayer::GetOrCreateBucket(std::string_view InBucket)
 
 	CacheBucket* Result = Bucket.get();
 	m_Buckets.emplace(BucketName, std::move(Bucket));
-
+	m_UpdateCaptureLock.WithExclusiveLock([&]() {
+		if (m_CapturedBuckets)
+		{
+			m_CapturedBuckets->push_back(std::string(BucketName));
+		}
+	});
 	return Result;
 }
 
@@ -4317,6 +4316,60 @@ ZenCacheDiskLayer::GetValueDetails(const std::string_view BucketFilter, const st
 	return Details;
 }
 
+std::vector<RwLock::SharedLockScope>
+ZenCacheDiskLayer::GetGcReferencerLocks()
+{
+	std::vector<RwLock::SharedLockScope> Locks;
+	Locks.emplace_back(RwLock::SharedLockScope(m_Lock));
+	for (auto& Kv : m_Buckets)
+	{
+		Locks.emplace_back(Kv.second->GetGcReferencerLock());
+	}
+	return Locks;
+}
+
+void
+ZenCacheDiskLayer::EnableUpdateCapture()
+{
+	m_UpdateCaptureLock.WithExclusiveLock([&]() {
+		if (m_UpdateCaptureRefCounter == 0)
+		{
+			ZEN_ASSERT(!m_CapturedBuckets);
+			m_CapturedBuckets = std::make_unique<std::vector<std::string>>();
+		}
+		else
+		{
+			ZEN_ASSERT(m_CapturedBuckets);
+		}
+		m_UpdateCaptureRefCounter++;
+	});
+}
+
+void
+ZenCacheDiskLayer::DisableUpdateCapture()
+{
+	m_UpdateCaptureLock.WithExclusiveLock([&]() {
+		ZEN_ASSERT(m_CapturedBuckets);
+		ZEN_ASSERT(m_UpdateCaptureRefCounter > 0);
+		m_UpdateCaptureRefCounter--;
+		if (m_UpdateCaptureRefCounter == 0)
+		{
+			m_CapturedBuckets.reset();
+		}
+	});
+}
+
+std::vector<std::string>
+ZenCacheDiskLayer::GetCapturedBuckets()
+{
+	RwLock::SharedLockScope _(m_UpdateCaptureLock);
+	if (m_CapturedBuckets)
+	{
+		return *m_CapturedBuckets;
+	}
+	return {};
+}
+
 void
 ZenCacheDiskLayer::MemCacheTrim()
 {
diff --git a/src/zenstore/cache/structuredcachestore.cpp b/src/zenstore/cache/structuredcachestore.cpp
index d9c2d3e59..d7d594af7 100644
--- a/src/zenstore/cache/structuredcachestore.cpp
+++ b/src/zenstore/cache/structuredcachestore.cpp
@@ -375,6 +375,23 @@ ZenCacheNamespace::GetValueDetails(const std::string_view BucketFilter, const st
 	return m_DiskLayer.GetValueDetails(BucketFilter, ValueFilter);
 }
 
+std::vector<RwLock::SharedLockScope>
+ZenCacheNamespace::GetGcReferencerLocks()
+{
+	return m_DiskLayer.GetGcReferencerLocks();
+}
+
+void
+ZenCacheNamespace::EnableUpdateCapture()
+{
+	m_DiskLayer.EnableUpdateCapture();
+}
+void
+ZenCacheNamespace::DisableUpdateCapture()
+{
+	m_DiskLayer.DisableUpdateCapture();
+}
+
 #if ZEN_WITH_TESTS
 void
 ZenCacheNamespace::SetAccessTime(std::string_view Bucket, const IoHash& HashKey, GcClock::TimePoint Time)
@@ -439,11 +456,15 @@ ZenCacheStore::ZenCacheStore(GcManager&					  Gc,
 												m_BasePath / fmt::format("{}{}", NamespaceDiskPrefix, NamespaceName),
 												m_Configuration.NamespaceConfig);
 	}
+	m_Gc.AddGcReferencer(*this);
+	m_Gc.AddGcReferenceLocker(*this);
 }
 
 ZenCacheStore::~ZenCacheStore()
 {
 	ZEN_INFO("closing cache store at '{}'", m_BasePath);
+	m_Gc.RemoveGcReferenceLocker(*this);
+	m_Gc.RemoveGcReferencer(*this);
 	SetLoggingConfig({.EnableWriteLog = false, .EnableAccessLog = false});
 	m_Namespaces.clear();
 }
@@ -844,6 +865,14 @@ ZenCacheStore::GetNamespace(std::string_view Namespace)
 																		  m_JobQueue,
 																		  m_BasePath / fmt::format("{}{}", NamespaceDiskPrefix, Namespace),
 																		  m_Configuration.NamespaceConfig));
+
+	m_UpdateCaptureLock.WithExclusiveLock([&]() {
+		if (m_CapturedNamespaces)
+		{
+			m_CapturedNamespaces->push_back(std::string(Namespace));
+		}
+	});
+
 	return NewNamespace.first->second.get();
 }
 
@@ -1003,6 +1032,212 @@ ZenCacheStore::GetBucketInfo(std::string_view NamespaceName, std::string_view Bu
 	return {};
 }
 
+std::vector<RwLock::SharedLockScope>
+ZenCacheStore::LockState(GcCtx&)
+{
+	std::vector<RwLock::SharedLockScope> Locks;
+	Locks.emplace_back(RwLock::SharedLockScope(m_NamespacesLock));
+	for (auto& NamespaceIt : m_Namespaces)
+	{
+		std::vector<RwLock::SharedLockScope> NamespaceLocks = NamespaceIt.second->GetGcReferencerLocks();
+		for (auto It = std::make_move_iterator(NamespaceLocks.begin()); It != std::make_move_iterator(NamespaceLocks.end()); It++)
+		{
+			Locks.emplace_back(std::move(*It));
+		}
+	}
+	return Locks;
+}
+
+void
+ZenCacheStore::EnableUpdateCapture()
+{
+	m_UpdateCaptureLock.WithExclusiveLock([&]() {
+		if (m_UpdateCaptureRefCounter == 0)
+		{
+			ZEN_ASSERT(!m_CapturedNamespaces);
+			m_CapturedNamespaces = std::make_unique<std::vector<std::string>>();
+		}
+		else
+		{
+			ZEN_ASSERT(m_CapturedNamespaces);
+		}
+		m_UpdateCaptureRefCounter++;
+	});
+	for (auto& NamespaceIt : m_Namespaces)
+	{
+		NamespaceIt.second->EnableUpdateCapture();
+	}
+}
+
+void
+ZenCacheStore::DisableUpdateCapture()
+{
+	for (auto& NamespaceIt : m_Namespaces)
+	{
+		NamespaceIt.second->DisableUpdateCapture();
+	}
+	m_UpdateCaptureLock.WithExclusiveLock([&]() {
+		ZEN_ASSERT(m_CapturedNamespaces);
+		ZEN_ASSERT(m_UpdateCaptureRefCounter > 0);
+		m_UpdateCaptureRefCounter--;
+		if (m_UpdateCaptureRefCounter == 0)
+		{
+			m_CapturedNamespaces.reset();
+		}
+	});
+}
+
+std::vector<std::string>
+ZenCacheStore::GetCapturedNamespaces()
+{
+	RwLock::SharedLockScope _(m_UpdateCaptureLock);
+	if (m_CapturedNamespaces)
+	{
+		return *m_CapturedNamespaces;
+	}
+	return {};
+}
+
+std::string
+ZenCacheStore::GetGcName(GcCtx&)
+{
+	return fmt::format("zencachestore: '{}'", m_BasePath.string());
+}
+
+GcStoreCompactor*
+ZenCacheStore::RemoveExpiredData(GcCtx&, GcStats&)
+{
+	return nullptr;
+}
+
+class CacheStoreReferenceChecker : public GcReferenceChecker
+{
+public:
+	CacheStoreReferenceChecker(ZenCacheStore& InCacheStore) : m_CacheStore(InCacheStore) { m_CacheStore.EnableUpdateCapture(); }
+
+	virtual ~CacheStoreReferenceChecker()
+	{
+		try
+		{
+			m_CacheStore.DisableUpdateCapture();
+		}
+		catch (const std::exception& Ex)
+		{
+			ZEN_ERROR("~CacheStoreReferenceChecker threw exception: '{}'", Ex.what());
+		}
+	}
+
+	virtual std::string GetGcName(GcCtx&) override { return "cachestore"; }
+	virtual void		PreCache(GcCtx&) override {}
+	virtual void		UpdateLockedState(GcCtx& Ctx) override
+	{
+		ZEN_TRACE_CPU("Z$::UpdateLockedState");
+
+		Stopwatch Timer;
+
+		std::vector<ZenCacheDiskLayer::CacheBucket*> AddedBuckets;
+
+		const auto _ = MakeGuard([&] {
+			if (!Ctx.Settings.Verbose)
+			{
+				return;
+			}
+			ZEN_INFO("GCV2: cachestore [LOCKSTATE] '{}': found {} references in {} in {} new buckets",
+					 "cachestore",
+					 m_References.size(),
+					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()),
+					 AddedBuckets.size());
+		});
+
+		std::vector<std::string> AddedNamespaces = m_CacheStore.GetCapturedNamespaces();
+
+		for (const std::string& AddedNamespace : AddedNamespaces)
+		{
+			if (auto It = m_CacheStore.m_Namespaces.find(AddedNamespace); It != m_CacheStore.m_Namespaces.end())
+			{
+				ZenCacheNamespace& Namespace = *It->second;
+				for (auto& BucketKV : Namespace.m_DiskLayer.m_Buckets)
+				{
+					AddedBuckets.push_back(BucketKV.second.get());
+				}
+			}
+		}
+		for (auto& NamepaceKV : m_CacheStore.m_Namespaces)
+		{
+			ZenCacheNamespace&		 Namespace			   = *NamepaceKV.second;
+			std::vector<std::string> NamespaceAddedBuckets = Namespace.m_DiskLayer.GetCapturedBuckets();
+			for (const std::string& AddedBucketName : NamespaceAddedBuckets)
+			{
+				if (auto It = Namespace.m_DiskLayer.m_Buckets.find(AddedBucketName); It != Namespace.m_DiskLayer.m_Buckets.end())
+				{
+					AddedBuckets.push_back(It->second.get());
+				}
+			}
+		}
+
+		for (ZenCacheDiskLayer::CacheBucket* Bucket : AddedBuckets)
+		{
+			bool Continue = Bucket->GetReferencesLocked(Ctx, m_References);
+			if (!Continue)
+			{
+				break;
+			}
+		}
+	}
+
+	virtual void RemoveUsedReferencesFromSet(GcCtx& Ctx, HashSet& IoCids) override
+	{
+		ZEN_TRACE_CPU("Z$::RemoveUsedReferencesFromSet");
+
+		size_t	   InitialCount = IoCids.size();
+		Stopwatch  Timer;
+		const auto _ = MakeGuard([&] {
+			if (!Ctx.Settings.Verbose)
+			{
+				return;
+			}
+			ZEN_INFO("GCV2: projectstore [FILTER REFERENCES] '{}': filtered out {} used references out of {} in {}",
+					 "projectstore",
+					 InitialCount - IoCids.size(),
+					 InitialCount,
+					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
+		});
+
+		for (const IoHash& ReferenceHash : m_References)
+		{
+			if (IoCids.erase(ReferenceHash) == 1)
+			{
+				if (IoCids.empty())
+				{
+					return;
+				}
+			}
+		}
+	}
+
+private:
+	ZenCacheStore&		m_CacheStore;
+	std::vector<IoHash> m_References;
+};
+
+std::vector<GcReferenceChecker*>
+ZenCacheStore::CreateReferenceCheckers(GcCtx& Ctx)
+{
+	ZEN_TRACE_CPU("CacheStore::CreateReferenceCheckers");
+
+	Stopwatch						 Timer;
+	const auto						 _ = MakeGuard([&] {
+		  if (!Ctx.Settings.Verbose)
+		  {
+			  return;
+		  }
+		  ZEN_INFO("GCV2: cachestore [CREATE CHECKERS] '{}': completed in {}", m_BasePath, NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
+	  });
+	std::vector<GcReferenceChecker*> Checkers;
+	Checkers.emplace_back(new CacheStoreReferenceChecker(*this));
+	return Checkers;
+}
+
 //////////////////////////////////////////////////////////////////////////
 
 #if ZEN_WITH_TESTS
diff --git a/src/zenstore/gc.cpp b/src/zenstore/gc.cpp
index e8cf6ec5e..8db34b9c5 100644
--- a/src/zenstore/gc.cpp
+++ b/src/zenstore/gc.cpp
@@ -382,7 +382,7 @@ WriteReferencerStats(CbObjectWriter& Writer, const GcReferencerStats& Stats, boo
 
 	Writer << "CreateReferenceCheckers" << ToTimeSpan(Stats.CreateReferenceCheckersMS);
 	Writer << "PreCacheState" << ToTimeSpan(Stats.PreCacheStateMS);
-	Writer << "LockState" << ToTimeSpan(Stats.LockStateMS);
+	Writer << "UpdateLockedState" << ToTimeSpan(Stats.UpdateLockedStateMS);
 	Writer << "Elapsed" << ToTimeSpan(Stats.ElapsedMS);
 };
 
@@ -452,6 +452,7 @@ WriteGCResult(CbObjectWriter& Writer, const GcResult& Result, bool HumanReadable
 	Writer << "CreateReferenceCheckers" << ToTimeSpan(Result.CreateReferenceCheckersMS);
 	Writer << "PreCacheState" << ToTimeSpan(Result.PreCacheStateMS);
 	Writer << "LockState" << ToTimeSpan(Result.LockStateMS);
+	Writer << "UpdateLockedState" << ToTimeSpan(Result.UpdateLockedStateMS);
 
 	Writer << "CreateReferencePruners" << ToTimeSpan(Result.CreateReferencePrunersMS);
 	Writer << "RemoveUnreferencedData" << ToTimeSpan(Result.RemoveUnreferencedDataMS);
@@ -510,7 +511,7 @@ void
 Sum(GcReferencerStats& Stat)
 {
 	Stat.ElapsedMS = Stat.RemoveExpiredDataStats.ElapsedMS + Stat.CompactStoreStats.ElapsedMS + Stat.CreateReferenceCheckersMS +
-					 Stat.PreCacheStateMS + Stat.LockStateMS;
+					 Stat.PreCacheStateMS + Stat.UpdateLockedStateMS;
 }
 
 void
@@ -521,7 +522,7 @@ Add(GcReferencerStats& Sum, const GcReferencerStats& Sub)
 
 	Sum.CreateReferenceCheckersMS += Sub.CreateReferenceCheckersMS;
 	Sum.PreCacheStateMS += Sub.PreCacheStateMS;
-	Sum.LockStateMS += Sub.LockStateMS;
+	Sum.UpdateLockedStateMS += Sub.UpdateLockedStateMS;
 
 	Sum.ElapsedMS += Sub.ElapsedMS;
 }
@@ -584,6 +585,19 @@ GcManager::RemoveGcReferencer(GcReferencer& Referencer)
 }
 
 void
+GcManager::AddGcReferenceLocker(GcReferenceLocker& ReferenceLocker)
+{
+	RwLock::ExclusiveLockScope _(m_Lock);
+	m_GcReferencerLockers.push_back(&ReferenceLocker);
+}
+void
+GcManager::RemoveGcReferenceLocker(GcReferenceLocker& ReferenceLocker)
+{
+	RwLock::ExclusiveLockScope _(m_Lock);
+	std::erase_if(m_GcReferencerLockers, [&](GcReferenceLocker* $) { return $ == &ReferenceLocker; });
+}
+
+void
 GcManager::AddGcReferenceStore(GcReferenceStore& ReferenceStore)
 {
 	RwLock::ExclusiveLockScope _(m_Lock);
@@ -879,59 +893,90 @@ GcManager::CollectGarbage(const GcSettings& Settings)
 					}
 				}
 
+				std::vector<RwLock::SharedLockScope> LockerScopes;
 				SCOPED_TIMER(uint64_t ElapsedMS = Timer.GetElapsedTimeMs(); Result.WriteBlockMS = std::chrono::milliseconds(ElapsedMS);
 							 ZEN_INFO("GCV2: Writes blocked for {}", NiceTimeSpanMs(ElapsedMS)));
 				{
-					ZEN_INFO("GCV2: Locking state for {} reference checkers", ReferenceCheckers.size());
 					if (!ReferenceCheckers.empty())
 					{
 						if (CheckGCCancel())
 						{
 							return Sum(Result, true);
 						}
-						ZEN_TRACE_CPU("GcV2::LockState");
-
-						// Locking all references checkers so we have a steady state of which references are used
-						// From this point we have blocked all writes to all References (DiskBucket/ProjectStore) until
-						// we delete the ReferenceCheckers
-						Latch WorkLeft(1);
-
+						ZEN_INFO("GCV2: Locking state for {} reference checkers", ReferenceCheckers.size());
 						{
-							SCOPED_TIMER(Result.LockStateMS = std::chrono::milliseconds(Timer.GetElapsedTimeMs());
-										 if (Ctx.Settings.Verbose) {
-											 ZEN_INFO("GCV2: Locked state using {} reference checkers in {}",
-													  ReferenceCheckers.size(),
-													  NiceTimeSpanMs(Result.LockStateMS.count()));
-										 });
-							for (auto& It : ReferenceCheckers)
+							ZEN_TRACE_CPU("GcV2::LockReferencers");
+							// From this point we have blocked all writes to all References (DiskBucket/ProjectStore) until
+							// we delete the ReferenceLockers
+							Latch WorkLeft(1);
 							{
-								if (CheckGCCancel())
+								SCOPED_TIMER(Result.LockStateMS = std::chrono::milliseconds(Timer.GetElapsedTimeMs());
+											 if (Ctx.Settings.Verbose) {
+												 ZEN_INFO("GCV2: Locked referencers using {} reference lockers in {}",
+														  ReferenceCheckers.size(),
+														  NiceTimeSpanMs(Result.LockStateMS.count()));
+											 });
+								for (GcReferenceLocker* ReferenceLocker : m_GcReferencerLockers)
 								{
-									WorkLeft.CountDown();
-									WorkLeft.Wait();
-									return Sum(Result, true);
-								}
-
-								GcReferenceChecker*						   Checker = It.first.get();
-								size_t									   Index   = It.second;
-								std::pair<std::string, GcReferencerStats>* Stats   = &Result.ReferencerStats[Index];
-								WorkLeft.AddCount(1);
-								ThreadPool.ScheduleWork([this, &Ctx, Checker, Index, Stats, &WorkLeft]() {
-									auto _ = MakeGuard([&WorkLeft]() { WorkLeft.CountDown(); });
-									try
+									std::vector<RwLock::SharedLockScope> LockScopes = ReferenceLocker->LockState(Ctx);
+									for (auto It = std::make_move_iterator(LockScopes.begin());
+										 It != std::make_move_iterator(LockScopes.end());
+										 It++)
 									{
-										SCOPED_TIMER(Stats->second.LockStateMS = std::chrono::milliseconds(Timer.GetElapsedTimeMs()););
-										Checker->LockState(Ctx);
+										LockerScopes.emplace_back(std::move(*It));
 									}
-									catch (const std::exception& Ex)
+								}
+							}
+						}
+						ZEN_INFO("GCV2: Updating locked state for {} reference checkers", ReferenceCheckers.size());
+						{
+							ZEN_TRACE_CPU("GcV2::UpdateLockedState");
+
+							// Locking all references checkers so we have a steady state of which references are used
+							// From this point we have blocked all writes to all References (DiskBucket/ProjectStore) until
+							// we delete the ReferenceCheckers
+							Latch WorkLeft(1);
+
+							{
+								SCOPED_TIMER(Result.UpdateLockedStateMS = std::chrono::milliseconds(Timer.GetElapsedTimeMs());
+											 if (Ctx.Settings.Verbose) {
+												 ZEN_INFO("GCV2: Updated locked state using {} reference checkers in {}",
+														  ReferenceCheckers.size(),
+														  NiceTimeSpanMs(Result.UpdateLockedStateMS.count()));
+											 });
+								for (auto& It : ReferenceCheckers)
+								{
+									if (CheckGCCancel())
 									{
-										ZEN_ERROR("GCV2: Failed locking state for {}. Reason: '{}'", Checker->GetGcName(Ctx), Ex.what());
-										SetCancelGC(true);
+										WorkLeft.CountDown();
+										WorkLeft.Wait();
+										return Sum(Result, true);
 									}
-								});
+
+									GcReferenceChecker*						   Checker = It.first.get();
+									size_t									   Index   = It.second;
+									std::pair<std::string, GcReferencerStats>* Stats   = &Result.ReferencerStats[Index];
+									WorkLeft.AddCount(1);
+									ThreadPool.ScheduleWork([this, &Ctx, Checker, Index, Stats, &WorkLeft]() {
+										auto _ = MakeGuard([&WorkLeft]() { WorkLeft.CountDown(); });
+										try
+										{
+											SCOPED_TIMER(Stats->second.UpdateLockedStateMS =
+															 std::chrono::milliseconds(Timer.GetElapsedTimeMs()););
+											Checker->UpdateLockedState(Ctx);
+										}
+										catch (const std::exception& Ex)
+										{
+											ZEN_ERROR("GCV2: Failed Updating locked state for {}. Reason: '{}'",
+													  Checker->GetGcName(Ctx),
+													  Ex.what());
+											SetCancelGC(true);
+										}
+									});
+								}
+								WorkLeft.CountDown();
+								WorkLeft.Wait();
 							}
-							WorkLeft.CountDown();
-							WorkLeft.Wait();
 						}
 					}
 				}
@@ -1020,6 +1065,7 @@ GcManager::CollectGarbage(const GcSettings& Settings)
 						}
 					}
 					// Let the GcReferencers add new data, we will only change on-disk data at this point, adding new data is allowed
+					LockerScopes.clear();
 					ReferenceCheckers.clear();
 					ReferencePruners.clear();
 				}
diff --git a/src/zenstore/include/zenstore/cache/cachedisklayer.h b/src/zenstore/include/zenstore/cache/cachedisklayer.h
index 9dee4d3f7..537f4396a 100644
--- a/src/zenstore/include/zenstore/cache/cachedisklayer.h
+++ b/src/zenstore/include/zenstore/cache/cachedisklayer.h
@@ -197,6 +197,12 @@ public:
 
 	CacheValueDetails::NamespaceDetails GetValueDetails(const std::string_view BucketFilter, const std::string_view ValueFilter) const;
 
+	std::vector<RwLock::SharedLockScope> GetGcReferencerLocks();
+
+	void					 EnableUpdateCapture();
+	void					 DisableUpdateCapture();
+	std::vector<std::string> GetCapturedBuckets();
+
 #if ZEN_WITH_TESTS
 	void SetAccessTime(std::string_view Bucket, const IoHash& HashKey, GcClock::TimePoint Time);
 #endif	// ZEN_WITH_TESTS
@@ -227,6 +233,8 @@ public:
 		void	 ScrubStorage(ScrubContext& Ctx);
 		void	 GatherReferences(GcContext& GcCtx);
 		void	 CollectGarbage(GcContext& GcCtx);
+		RwLock::SharedLockScope GetGcReferencerLock();
+		bool					GetReferencesLocked(GcCtx& Ctx, std::vector<IoHash>& OutReferences);
 
 		inline GcStorageSize StorageSize() const
 		{
@@ -461,12 +469,16 @@ private:
 	mutable RwLock												  m_Lock;
 	std::unordered_map<std::string, std::unique_ptr<CacheBucket>> m_Buckets;
 	std::vector<std::unique_ptr<CacheBucket>>					  m_DroppedBuckets;
+	mutable RwLock												  m_UpdateCaptureLock;
+	uint32_t													  m_UpdateCaptureRefCounter = 0;
+	std::unique_ptr<std::vector<std::string>>					  m_CapturedBuckets;
 
 	ZenCacheDiskLayer(const ZenCacheDiskLayer&) = delete;
 	ZenCacheDiskLayer& operator=(const ZenCacheDiskLayer&) = delete;
 
 	friend class DiskBucketStoreCompactor;
 	friend class DiskBucketReferenceChecker;
+	friend class CacheStoreReferenceChecker;
 };
 
 }  // namespace zen
diff --git a/src/zenstore/include/zenstore/cache/structuredcachestore.h b/src/zenstore/include/zenstore/cache/structuredcachestore.h
index 7460d01ce..9160db667 100644
--- a/src/zenstore/include/zenstore/cache/structuredcachestore.h
+++ b/src/zenstore/include/zenstore/cache/structuredcachestore.h
@@ -48,6 +48,7 @@ class JobQueue;
    projects from each other.
 
  */
+
 class ZenCacheNamespace final : public GcStorage, public GcContributor
 {
 public:
@@ -118,6 +119,11 @@ public:
 
 	CacheValueDetails::NamespaceDetails GetValueDetails(const std::string_view BucketFilter, const std::string_view ValueFilter) const;
 
+	std::vector<RwLock::SharedLockScope> GetGcReferencerLocks();
+
+	void EnableUpdateCapture();
+	void DisableUpdateCapture();
+
 #if ZEN_WITH_TESTS
 	void SetAccessTime(std::string_view Bucket, const IoHash& HashKey, GcClock::TimePoint Time);
 #endif	// ZEN_WITH_TESTS
@@ -137,6 +143,8 @@ private:
 
 	ZenCacheNamespace(const ZenCacheNamespace&) = delete;
 	ZenCacheNamespace& operator=(const ZenCacheNamespace&) = delete;
+
+	friend class CacheStoreReferenceChecker;
 };
 
 /** Cache store interface
@@ -145,7 +153,7 @@ private:
 
   */
 
-class ZenCacheStore final : public RefCounted, public StatsProvider
+class ZenCacheStore final : public RefCounted, public StatsProvider, public GcReferencer, public GcReferenceLocker
 {
 public:
 	static constexpr std::string_view DefaultNamespace =
@@ -271,6 +279,16 @@ public:
 	// StatsProvider
 	virtual void ReportMetrics(StatsMetrics& Statsd) override;
 
+	virtual std::vector<RwLock::SharedLockScope> LockState(GcCtx& Ctx) override;
+
+	virtual std::string						 GetGcName(GcCtx& Ctx) override;
+	virtual GcStoreCompactor*				 RemoveExpiredData(GcCtx& Ctx, GcStats& Stats) override;
+	virtual std::vector<GcReferenceChecker*> CreateReferenceCheckers(GcCtx& Ctx) override;
+
+	void					 EnableUpdateCapture();
+	void					 DisableUpdateCapture();
+	std::vector<std::string> GetCapturedNamespaces();
+
 private:
 	const ZenCacheNamespace* FindNamespace(std::string_view Namespace) const;
 	ZenCacheNamespace*		 GetNamespace(std::string_view Namespace);
@@ -283,6 +301,9 @@ private:
 	mutable RwLock									m_NamespacesLock;
 	NamespaceMap									m_Namespaces;
 	std::vector<std::unique_ptr<ZenCacheNamespace>> m_DroppedNamespaces;
+	mutable RwLock									m_UpdateCaptureLock;
+	uint32_t										m_UpdateCaptureRefCounter = 0;
+	std::unique_ptr<std::vector<std::string>>		m_CapturedNamespaces;
 
 	GcManager&			  m_Gc;
 	JobQueue&			  m_JobQueue;
@@ -314,6 +335,8 @@ private:
 	std::thread				   m_AsyncLoggingThread;
 	std::atomic_bool		   m_WriteLogEnabled;
 	std::atomic_bool		   m_AccessLogEnabled;
+
+	friend class CacheStoreReferenceChecker;
 };
 
 void structured_cachestore_forcelink();
diff --git a/src/zenstore/include/zenstore/gc.h b/src/zenstore/include/zenstore/gc.h
index 5262c6d2e..c3a71baa6 100644
--- a/src/zenstore/include/zenstore/gc.h
+++ b/src/zenstore/include/zenstore/gc.h
@@ -88,7 +88,7 @@ struct GcReferencerStats
 
 	std::chrono::milliseconds CreateReferenceCheckersMS = {};
 	std::chrono::milliseconds PreCacheStateMS			= {};
-	std::chrono::milliseconds LockStateMS				= {};
+	std::chrono::milliseconds UpdateLockedStateMS		= {};
 	std::chrono::milliseconds ElapsedMS					= {};
 };
 
@@ -115,6 +115,7 @@ struct GcResult
 	std::chrono::milliseconds CreateReferenceCheckersMS = {};
 	std::chrono::milliseconds PreCacheStateMS			= {};
 	std::chrono::milliseconds LockStateMS				= {};
+	std::chrono::milliseconds UpdateLockedStateMS		= {};
 
 	std::chrono::milliseconds CreateReferencePrunersMS = {};
 	std::chrono::milliseconds RemoveUnreferencedDataMS = {};
@@ -177,13 +178,19 @@ public:
 
 	virtual std::string GetGcName(GcCtx& Ctx) = 0;
 
+	// Read as much of the current state - nothing is locked for you here so you need to lock as appropriate
 	virtual void PreCache(GcCtx& Ctx) = 0;
 
-	// Lock the state and make sure no references changes, usually a read-lock is taken until the destruction
-	// of the instance. Called once before any calls to RemoveUsedReferencesFromSet
-	// The implementation should be as fast as possible as LockState is part of a stop the world (from changes)
-	// until all instances of GcReferenceChecker are deleted
-	virtual void LockState(GcCtx& Ctx) = 0;
+	// Update the state after all ReferenceCheckers has completed PreCache and all ReferenceLockers has
+	// completed their LockState operation.
+	// At this stage all data that UpdateLockedState needs to touch should be locked by the ReferenceLockers.
+	// *IMPORTANT* Do *not* take any locks (shared or exclusive) in this code.
+	// This is because we need to acquire the locks in an ordered manner and not end up in a deadlock due to other code
+	// trying to get exclusive locks halfway through our execution.
+	// Called once before any calls to RemoveUsedReferencesFromSet.
+	// The implementation should be as fast as possible as UpdateLockedState is part of a stop the world (from changes)
+	// until all instances of GcReferenceChecker UpdateLockedState are completed
+	virtual void UpdateLockedState(GcCtx& Ctx) = 0;
 
 	// Go through IoCids and see which ones are referenced. If it is the reference must be removed from IoCids
 	// This function should use pre-cached information on what is referenced as we are in stop the world mode
@@ -191,6 +198,22 @@ public:
 };
 
 /**
+ * @brief An interface to implement a lock for Stop The World (from writing new data)
+ *
+ * This interface is registered/unregistered to GcManager vua AddGcReferenceLocker() and RemoveGcReferenceLockerr()
+ */
+class GcReferenceLocker
+{
+public:
+	virtual ~GcReferenceLocker() = default;
+
+	// Take all the locks needed to execute UpdateLockedState for the all the GcReferenceChecker in your domain
+	// Once all the GcReferenceChecker has executed UpdateLockedState and RemoveUsedReferencesFromSet for all
+	// domains has completed, the locks will be disposed and writes are allowed once again
+	virtual std::vector<RwLock::SharedLockScope> LockState(GcCtx& Ctx) = 0;
+};
+
+/**
  * @brief Interface to handle GC of data that references Cid data
  *
  * This interface is registered/unregistered to GcManager vua AddGcReferencer() and RemoveGcReferencer()
@@ -203,7 +226,7 @@ protected:
 public:
 	virtual std::string GetGcName(GcCtx& Ctx) = 0;
 
-	// Remove expired data based on either GcCtx::Settings CacheExpireTime/ProjectExpireTime
+	// Remove expired data based on either GcCtx::Settings CacheExpireTime or ProjectExpireTime
 	virtual GcStoreCompactor* RemoveExpiredData(GcCtx& Ctx, GcStats& Stats) = 0;
 
 	// Create 0-n GcReferenceChecker for this GcReferencer. Caller will manage lifetime of
@@ -350,6 +373,9 @@ public:
 	void AddGcReferencer(GcReferencer& Referencer);
 	void RemoveGcReferencer(GcReferencer& Referencer);
 
+	void AddGcReferenceLocker(GcReferenceLocker& ReferenceLocker);
+	void RemoveGcReferenceLocker(GcReferenceLocker& ReferenceLocker);
+
 	void AddGcReferenceStore(GcReferenceStore& ReferenceStore);
 	void RemoveGcReferenceStore(GcReferenceStore& ReferenceStore);
 
@@ -382,8 +408,9 @@ private:
 	CidStore*					m_CidStore		   = nullptr;
 	const DiskWriteBlocker*		m_DiskWriteBlocker = nullptr;
 
-	std::vector<GcReferencer*>	   m_GcReferencers;
-	std::vector<GcReferenceStore*> m_GcReferenceStores;
+	std::vector<GcReferencer*>		m_GcReferencers;
+	std::vector<GcReferenceLocker*> m_GcReferencerLockers;
+	std::vector<GcReferenceStore*>	m_GcReferenceStores;
 
 	std::atomic_bool m_CancelGC{false};
 };