gc block size target max size (#180)

* If a block is small (less than half max size) we add it to blocks to compact
Sort blocks when iterating over them
* do compact of block stores even if no new unused are found
* do compact phase even if bucket is empty

1 files changed, 31 insertions, 8 deletions

diff --git a/src/zenstore/blockstore.cpp b/src/zenstore/blockstore.cpp
index 592d1c7fb..2ae51d627 100644
--- a/src/zenstore/blockstore.cpp
+++ b/src/zenstore/blockstore.cpp
@@ -383,6 +383,11 @@ BlockStore::GetBlocksToCompact(const BlockUsageMap& BlockUsage, uint32_t BlockUs
 	BlockEntryCountMap Result;
 	{
 		RwLock::SharedLockScope InsertLock(m_InsertLock);
+
+		const uint64_t SmallBlockLimit = m_MaxBlockSize / 2;
+
+		std::vector<uint32_t> SmallBlockIndexes;
+
 		for (const auto& It : m_ChunkBlocks)
 		{
 			uint32_t BlockIndex = It.first;
@@ -403,35 +408,53 @@ BlockStore::GetBlocksToCompact(const BlockUsageMap& BlockUsage, uint32_t BlockUs
 				UsedCount = UsageIt->second.EntryCount;
 			}
 
-			uint64_t BlockSize = It.second ? It.second->FileSize() : 0u;
-			if (BlockSize == 0)
+			uint64_t PhysicalSize = It.second ? It.second->FileSize() : 0u;
+			if (PhysicalSize == 0)
 			{
 				Result.insert_or_assign(BlockIndex, UsedCount);
 				continue;
 			}
 
+			bool IsBelowUnusedLimit = false;
+
 			if (BlockUsageThresholdPercent == 100)
 			{
-				if (UsedSize < BlockSize)
+				if (UsedSize < PhysicalSize)
 				{
-					Result.insert_or_assign(BlockIndex, UsedCount);
+					IsBelowUnusedLimit = true;
 				}
 			}
 			else if (BlockUsageThresholdPercent == 0)
 			{
 				if (UsedSize == 0)
 				{
-					Result.insert_or_assign(BlockIndex, UsedCount);
+					IsBelowUnusedLimit = true;
 				}
 			}
 			else
 			{
-				const uint32_t UsedPercent = UsedSize < BlockSize ? gsl::narrow<uint32_t>((100 * UsedSize) / BlockSize) : 100u;
+				const uint32_t UsedPercent = UsedSize < PhysicalSize ? gsl::narrow<uint32_t>((100 * UsedSize) / PhysicalSize) : 100u;
 				if (UsedPercent < BlockUsageThresholdPercent)
 				{
-					Result.insert_or_assign(BlockIndex, UsedCount);
+					IsBelowUnusedLimit = true;
 				}
 			}
+
+			if (IsBelowUnusedLimit)
+			{
+				Result.insert_or_assign(BlockIndex, UsedCount);
+			}
+			else if (PhysicalSize < SmallBlockLimit)
+			{
+				Result.insert_or_assign(BlockIndex, UsedCount);
+				SmallBlockIndexes.push_back(BlockIndex);
+			}
+		}
+
+		// If we only find one small block to compact, let it be.
+		if (SmallBlockIndexes.size() == 1 && Result.size() == 1)
+		{
+			Result.erase(SmallBlockIndexes[0]);
 		}
 	}
 	return Result;
@@ -1569,7 +1592,7 @@ BlockStore::CompactBlocks(const BlockStoreCompactState&	  CompactState,
 					 KeepChunkIndexes.size(),
 					 NiceBytes(MovedFromBlock),
 					 GetBlockPath(m_BlocksBasePath, BlockIndex).filename(),
-					 NiceBytes(OldBlockSize - MovedFromBlock));
+					 OldBlockSize > MovedFromBlock ? NiceBytes(OldBlockSize - MovedFromBlock) : 0);
 		}
 		if (TargetFileBuffer)
 		{