wipe cache buckets block store that may contain invalid state (#300)

* wipe cache buckets block store that may contain invalid state
* Update CHANGELOG.md

2 files changed, 16 insertions, 2 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 47ce391df..afdf09bc9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,10 +1,10 @@
 ##
 - Feature: Gracefully exit if Ctrl-C is pressed
-- Feature: Structured cache now writes an activity log to `logs/c$` which may be used to understand client interactions better. Enabled by default for the time being
+- Feature: Structured cache now writes an activity log to `logs/z$` which may be used to understand client interactions better. Enabled by default for the time being
 - Bugfix: Return error code on exit as set by application
 - Bugfix: Fix crash at startup if dead process handles are detected in ZenServerState
 - Bugfix: Fixed assert/error when running block store GC and a block to GC does not exist
-- Bugfix: GC could mix up locations of cache bucket items causing it to return the wrong item for a specific key
+- Bugfix: GC could mix up locations of cache bucket items causing it to return the wrong item for a specific key. All cache buckets from previous versions will be wiped to remove inconsistent state
 - Improvement: Log details about file and read operation when it fails inside IoBuffer::Materialize()
 
 ## 0.2.10
diff --git a/src/zenserver/cache/structuredcachestore.cpp b/src/zenserver/cache/structuredcachestore.cpp
index 2fd8e8be8..7368d45da 100644
--- a/src/zenserver/cache/structuredcachestore.cpp
+++ b/src/zenserver/cache/structuredcachestore.cpp
@@ -49,6 +49,12 @@ namespace {
 #pragma pack(push)
 #pragma pack(1)
 
+	// We use this to indicate if a on disk bucket needs wiping
+	// In version 0.2.5 -> 0.2.11 there was a GC corruption bug that would scrable the references
+	// to block items.
+	// See: https://github.com/EpicGames/zen/pull/299
+	static const uint32_t CurrentDiskBucketVersion = 1;
+
 	struct CacheBucketIndexHeader
 	{
 		static constexpr uint32_t ExpectedMagic	 = 0x75696478;	// 'uidx';
@@ -720,6 +726,12 @@ ZenCacheDiskLayer::CacheBucket::OpenOrCreate(std::filesystem::path BucketDir, bo
 		{
 			return false;
 		}
+		uint32_t Version = Manifest["Version"sv].AsUInt32(0);
+		if (Version != CurrentDiskBucketVersion)
+		{
+			ZEN_INFO("Wiping bucket '{}', found version {}, required version {}", BucketDir, Version, CurrentDiskBucketVersion);
+			IsNew = true;
+		}
 	}
 	else if (AllowCreate)
 	{
@@ -727,6 +739,7 @@ ZenCacheDiskLayer::CacheBucket::OpenOrCreate(std::filesystem::path BucketDir, bo
 
 		CbObjectWriter Writer;
 		Writer << "BucketId"sv << m_BucketId;
+		Writer << "Version"sv << CurrentDiskBucketVersion;
 		Manifest = Writer.Save();
 		SaveCompactBinaryObject(ManifestPath, Manifest);
 		IsNew = true;
@@ -1250,6 +1263,7 @@ ZenCacheDiskLayer::CacheBucket::SaveManifest()
 
 	CbObjectWriter Writer;
 	Writer << "BucketId"sv << m_BucketId;
+	Writer << "Version"sv << CurrentDiskBucketVersion;
 
 	if (!m_Index.empty())
 	{