Expose Reset (#558)

* exposed Reset()

* exposed Reset()

* unimplemented commit

* complete reset

* complete reset

* complete reset

* better reset

* finished Reset

* fixed memory mutation

Co-authored-by: giuliorebuffo <giuliorebuffo@system76-pc.localdomain>

kv/kv_interface.go

@@ -264,6 +264,7 @@ type RwTx interface {
 	// CollectMetrics - does collect all DB-related and Tx-related metrics
 	// this method exists only in RwTx to avoid concurrency
 	CollectMetrics()
+	Reset() error
 }
 
 // BucketMigrator used for buckets migration, don't use it in usual app code

kv/mdbx/kv_mdbx.go

@@ -1046,6 +1046,28 @@ func (tx *MdbxTx) DBSize() (uint64, error) {
 	return info.Geo.Current, err
 }
 
+func (tx *MdbxTx) Reset() (err error) {
+	tx.Rollback()
+	//tx.printDebugInfo()
+	if tx.db.closed.Load() {
+		return fmt.Errorf("db closed")
+	}
+	runtime.LockOSThread()
+	defer func() {
+		if err == nil {
+			tx.db.wg.Add(1)
+		}
+	}()
+
+	tx.tx, err = tx.db.env.BeginTxn(nil, 0)
+	if err != nil {
+		runtime.UnlockOSThread() // unlock only in case of error. normal flow is "defer .Rollback()"
+		return fmt.Errorf("%w, lable: %s, trace: %s", err, tx.db.opts.label.String(), stack2.Trace().String())
+	}
+	tx.tx.RawRead = true
+	return nil
+}
+
 func (tx *MdbxTx) RwCursor(bucket string) (kv.RwCursor, error) {
 	b := tx.db.buckets[bucket]
 	if b.AutoDupSortKeysConversion {

kv/memdb/memory_mutation.go

@@ -374,7 +374,10 @@ func (m *MemoryMutation) Cursor(bucket string) (kv.Cursor, error) {
 	return m.makeCursor(bucket)
 }
 
-// ViewID creates a new cursor (the real fun begins here)
 func (m *MemoryMutation) ViewID() uint64 {
 	panic("ViewID Not implemented")
 }
+
+func (m *MemoryMutation) Reset() error {
+	return nil
+}