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

1 files changed, 18 insertions, 5 deletions

diff --git a/src/zenstore/filecas.cpp b/src/zenstore/filecas.cpp
index 0d742d7e1..fe568a487 100644
--- a/src/zenstore/filecas.cpp
+++ b/src/zenstore/filecas.cpp
@@ -795,6 +795,21 @@ FileCasStrategy::IterateChunks(std::function<void(const IoHash& Hash, IoBuffer&&
 }
 
 void
+FileCasStrategy::IterateChunks(std::function<void(const IoHash& Hash, uint64_t Size)>&& Callback)
+{
+	ZEN_TRACE_CPU("FileCas::IterateChunks");
+
+	ZEN_ASSERT(m_IsInitialized);
+
+	RwLock::SharedLockScope _(m_Lock);
+	for (const auto& It : m_Index)
+	{
+		const IoHash& NameHash = It.first;
+		Callback(NameHash, It.second.Size);
+	}
+}
+
+void
 FileCasStrategy::Flush()
 {
 	ZEN_TRACE_CPU("FileCas::Flush");
@@ -927,7 +942,7 @@ FileCasStrategy::CollectGarbage(GcContext& GcCtx)
 
 	{
 		ZEN_TRACE_CPU("FileCas::CollectGarbage::Filter");
-		IterateChunks([&](const IoHash& Hash, IoBuffer&& Payload) {
+		IterateChunks([&](const IoHash& Hash, uint64_t Size) {
 			bool KeepThis	= false;
 			CandidateCas[0] = Hash;
 			GcCtx.FilterCids(CandidateCas, [&](const IoHash& Hash) {
@@ -935,16 +950,14 @@ FileCasStrategy::CollectGarbage(GcContext& GcCtx)
 				KeepThis = true;
 			});
 
-			const uint64_t FileSize = Payload.GetSize();
-
 			if (!KeepThis)
 			{
 				ChunksToDelete.push_back(Hash);
-				ChunksToDeleteBytes.fetch_add(FileSize);
+				ChunksToDeleteBytes.fetch_add(Size);
 			}
 
 			++ChunkCount;
-			ChunkBytes.fetch_add(FileSize);
+			ChunkBytes.fetch_add(Size);
 		});
 	}