Make blob related VersionEdit tags unignorable (facebook#7886)

Summary:
BlobFileAddition and BlobFileGarbage should not be in the ignorable tag
range, since if they are present in the MANIFEST, users cannot downgrade
to a RocksDB version that does not understand them without losing access
to the data in the blob files. The patch moves these two tags to the
unignorable range; this should still be safe at this point, since the
integrated BlobDB project is still work in progress and thus there
shouldn't be any ignorable BlobFileAddition/BlobFileGarbage tags out
there.

Pull Request resolved: facebook#7886

Test Plan: `make check`

Reviewed By: cheng-chang

Differential Revision: D25980956

Pulled By: ltamasi

fbshipit-source-id: 13cf5bd61d77f049b513ecd5ad0be8c637e40a9d

db/version_edit.cc

@@ -556,7 +556,8 @@ Status VersionEdit::DecodeFrom(const Slice& src) {
         break;
       }
 
-      case kBlobFileAddition: {
+      case kBlobFileAddition:
+      case kBlobFileAddition_DEPRECATED: {
         BlobFileAddition blob_file_addition;
         const Status s = blob_file_addition.DecodeFrom(&input);
         if (!s.ok()) {
@@ -567,7 +568,8 @@ Status VersionEdit::DecodeFrom(const Slice& src) {
         break;
       }
 
-      case kBlobFileGarbage: {
+      case kBlobFileGarbage:
+      case kBlobFileGarbage_DEPRECATED: {
         BlobFileGarbage blob_file_garbage;
         const Status s = blob_file_garbage.DecodeFrom(&input);
         if (!s.ok()) {

db/version_edit.h

@@ -52,13 +52,16 @@ enum Tag : uint32_t {
 
   kInAtomicGroup = 300,
 
+  kBlobFileAddition = 400,
+  kBlobFileGarbage,
+
   // Mask for an unidentified tag from the future which can be safely ignored.
   kTagSafeIgnoreMask = 1 << 13,
 
   // Forward compatible (aka ignorable) records
   kDbId,
-  kBlobFileAddition,
-  kBlobFileGarbage,
+  kBlobFileAddition_DEPRECATED,
+  kBlobFileGarbage_DEPRECATED,
   kWalAddition,
   kWalDeletion,
   kFullHistoryTsLow,