Fix log index snapshot (#210)

* Fix log reading for structured cache store
Make sure cache is flushed at exit
* dont flush index to disk unless new entries have been written
* changelog

1 files changed, 17 insertions, 12 deletions

diff --git a/zenserver/cache/structuredcachestore.cpp b/zenserver/cache/structuredcachestore.cpp
index 9f6707a4a..de1243ddd 100644
--- a/zenserver/cache/structuredcachestore.cpp
+++ b/zenserver/cache/structuredcachestore.cpp
@@ -50,7 +50,7 @@ namespace {
 	struct CacheBucketIndexHeader
 	{
 		static constexpr uint32_t ExpectedMagic	 = 0x75696478;	// 'uidx';
-		static constexpr uint32_t CurrentVersion = 1;
+		static constexpr uint32_t CurrentVersion = 2;
 
 		uint32_t Magic			  = ExpectedMagic;
 		uint32_t Version		  = CurrentVersion;
@@ -649,6 +649,12 @@ ZenCacheDiskLayer::CacheBucket::OpenOrCreate(std::filesystem::path BucketDir, bo
 void
 ZenCacheDiskLayer::CacheBucket::MakeIndexSnapshot()
 {
+	uint64_t LogCount = m_SlogFile.GetLogCount();
+	if (m_LogFlushPosition == LogCount)
+	{
+		return;
+	}
+
 	ZEN_DEBUG("write store snapshot for '{}'", m_BucketDir / m_BucketName);
 	uint64_t   EntryCount = 0;
 	Stopwatch  Timer;
@@ -676,10 +682,7 @@ ZenCacheDiskLayer::CacheBucket::MakeIndexSnapshot()
 
 	try
 	{
-		m_SlogFile.Flush();
-
 		// Write the current state of the location map to a new index state
-		uint64_t					LogCount = 0;
 		std::vector<DiskIndexEntry> Entries;
 
 		{
@@ -692,8 +695,6 @@ ZenCacheDiskLayer::CacheBucket::MakeIndexSnapshot()
 				IndexEntry.Key			   = Entry.first;
 				IndexEntry.Location		   = Entry.second.Location;
 			}
-
-			LogCount = m_SlogFile.GetLogCount();
 		}
 
 		BasicFile ObjectIndexFile;
@@ -708,7 +709,8 @@ ZenCacheDiskLayer::CacheBucket::MakeIndexSnapshot()
 		ObjectIndexFile.Write(Entries.data(), Entries.size() * sizeof(DiskIndexEntry), sizeof(CacheBucketIndexHeader));
 		ObjectIndexFile.Flush();
 		ObjectIndexFile.Close();
-		EntryCount = Entries.size();
+		EntryCount		   = Entries.size();
+		m_LogFlushPosition = LogCount;
 	}
 	catch (std::exception& Err)
 	{
@@ -787,9 +789,10 @@ ZenCacheDiskLayer::CacheBucket::ReadLog(uint64_t SkipEntryCount)
 	std::filesystem::path LogPath = GetLogPath(m_BucketDir, m_BucketName);
 	if (std::filesystem::is_regular_file(LogPath))
 	{
+		uint64_t					LogEntryCount = 0;
 		Stopwatch					Timer;
 		const auto					_ = MakeGuard([&] {
-			 ZEN_INFO("read store '{}' log containing #{} entries in {}", LogPath, m_Index.size(), NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
+			 ZEN_INFO("read store '{}' log containing #{} entries in {}", LogPath, LogEntryCount, NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
 		 });
 		TCasLogFile<DiskIndexEntry> CasLog;
 		CasLog.Open(LogPath, CasLogFile::Mode::kRead);
@@ -801,8 +804,8 @@ ZenCacheDiskLayer::CacheBucket::ReadLog(uint64_t SkipEntryCount)
 				ZEN_WARN("reading full log at '{}', reason: Log position from index snapshot is out of range", LogPath);
 				SkipEntryCount = 0;
 			}
-			uint64_t ReadCount = EntryCount - SkipEntryCount;
-			m_Index.reserve(ReadCount);
+			LogEntryCount = EntryCount - SkipEntryCount;
+			m_Index.reserve(LogEntryCount);
 			uint64_t InvalidEntryCount = 0;
 			CasLog.Replay(
 				[&](const DiskIndexEntry& Record) {
@@ -825,6 +828,7 @@ ZenCacheDiskLayer::CacheBucket::ReadLog(uint64_t SkipEntryCount)
 			{
 				ZEN_WARN("found #{} invalid entries in '{}'", InvalidEntryCount, m_BucketDir / m_BucketName);
 			}
+			return LogEntryCount;
 		}
 	}
 	return 0;
@@ -849,8 +853,8 @@ ZenCacheDiskLayer::CacheBucket::OpenLog(const fs::path& BucketDir, const bool Is
 		fs::remove_all(m_BlocksBasePath);
 	}
 
-	uint64_t LogPosition   = ReadIndexFile();
-	uint64_t LogEntryCount = ReadLog(LogPosition);
+	m_LogFlushPosition	   = ReadIndexFile();
+	uint64_t LogEntryCount = ReadLog(m_LogFlushPosition);
 
 	CreateDirectories(m_BucketDir);
 
@@ -987,6 +991,7 @@ ZenCacheDiskLayer::CacheBucket::Flush()
 	m_BlockStore.Flush();
 
 	RwLock::SharedLockScope _(m_IndexLock);
+	m_SlogFile.Flush();
 	MakeIndexSnapshot();
 	SaveManifest();
 }