feat: allow saving version 0

Author: kocubinski

mutable_tree.go

@@ -40,6 +40,7 @@ type MutableTree struct {
 	unsavedFastNodeRemovals  *sync.Map      // map[string]interface{} FastNodes that have not yet been removed from disk
 	ndb                      *nodeDB
 	skipFastStorageUpgrade   bool // If true, the tree will work like no fast storage and always not upgrade fast storage
+	initialVersionSet        bool
 
 	mtx sync.Mutex
 }
@@ -146,8 +147,9 @@ func (tree *MutableTree) WorkingHash() []byte {
 
 func (tree *MutableTree) WorkingVersion() int64 {
 	version := tree.version + 1
-	if version == 1 && tree.ndb.opts.InitialVersion > 0 {
+	if version == 1 && tree.initialVersionSet {
 		version = int64(tree.ndb.opts.InitialVersion)
+		tree.initialVersionSet = false
 	}
 	return version
 }
@@ -459,11 +461,11 @@ func (tree *MutableTree) LoadVersion(targetVersion int64) (int64, error) {
 			tree.ndb.opts.InitialVersion, firstVersion)
 	}
 
-	if latestVersion < targetVersion {
+	if latestVersion >= 0 && latestVersion < targetVersion {
 		return latestVersion, fmt.Errorf("wanted to load target %d but only found up to %d", targetVersion, latestVersion)
 	}
 
-	if firstVersion == 0 {
+	if firstVersion <= 0 {
 		if targetVersion <= 0 {
 			if !tree.skipFastStorageUpgrade {
 				tree.mtx.Lock()
@@ -871,6 +873,7 @@ func (tree *MutableTree) saveFastNodeRemovals() error {
 // and is otherwise ignored.
 func (tree *MutableTree) SetInitialVersion(version uint64) {
 	tree.ndb.opts.InitialVersion = version
+	tree.initialVersionSet = true
 }
 
 // DeleteVersionsTo removes versions upto the given version from the MutableTree.

nodedb.go

@@ -838,7 +838,7 @@ func (ndb *nodeDB) getLatestVersion() (int64, error) {
 		return latestVersion, nil
 	}
 
-	return 0, nil
+	return -1, nil
 }
 
 func (ndb *nodeDB) resetLatestVersion(version int64) {