Merge branch 'mikers/BadgerVersions' of github.com:filecoin-project/l…

…otus into mikers/BadgerVersions

blockstore/badger/versions/badger.go

@@ -40,7 +40,7 @@ func OpenBadgerDB(opts Options) (BadgerDB, error) {
 			db = BadgerDB(&BadgerV2{dbV2})
 		}
 	default:
-		return nil, errors.New("unsupported badger version")
+		err = fmt.Errorf("unsupported badger version: %v", opts.BadgerVersion)
 	}
 
 	if err != nil {

node/config/types.go

@@ -482,9 +482,17 @@ type Pubsub struct {
 }
 
 type Chainstore struct {
+	// EXPERIMENTAL FEATURE. USE WITH CAUTION
+	// BadgerVersion switches the version of the Badger database engine. The default is 2 which has
+	// been well-tested and widely deployed. Switching this to version 4 will enable the new version
+	// of Badger, but the blockstore will be incompatible with Lotus running with version 2. Switching
+	// versions can only be done when the blockstore is empty and will be repopulated from a snapshot
+	// or chain sync. It cannot be upgraded or downgraded with existing data and there is currently
+	// no automatic migration tooling.
+	// This is an experimental feature and should not be used in production.
+	BadgerVersion    int
 	EnableSplitstore bool
 	Splitstore       Splitstore
-	BadgerVersion    int
 }
 
 type Splitstore struct {