metadata_type: add Serialization type

Ignore it while reading sstable 3_x and throw
if it's present when reading 2_x.

Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>

sstables/sstables.cc

@@ -63,6 +63,7 @@
 #include "integrity_checked_file_impl.hh"
 #include "service/storage_service.hh"
 #include "db/extensions.hh"
+#include "unimplemented.hh"
 
 thread_local disk_error_signal_type sstable_read_error;
 thread_local disk_error_signal_type sstable_write_error;
@@ -750,6 +751,15 @@ future<> parse(sstable_version_types v, random_access_reader& in, statistics& s)
                     return parse<compaction_metadata>(v, in, s.contents[val.first]);
                 case metadata_type::Stats:
                     return parse<stats_metadata>(v, in, s.contents[val.first]);
+                case metadata_type::Serialization:
+                    if (v != sstable_version_types::mc) {
+                        throw std::runtime_error(
+                            "Statistics is malformed: SSTable is in 2.x format but contains serialization header.");
+                    } else {
+                        // Ignore
+                        warn(unimplemented::cause::SSTABLE_FORMAT_M);
+                    }
+                    return make_ready_future<>();
                 default:
                     sstlog.warn("Invalid metadata type at Statistics file: {} ", int(val.first));
                     return make_ready_future<>();

sstables/types.hh

@@ -388,6 +388,7 @@ enum class metadata_type : uint32_t {
     Validation = 0,
     Compaction = 1,
     Stats = 2,
+    Serialization = 3,
 };
 
 enum class scylla_metadata_type : uint32_t {

unimplemented.cc

@@ -61,6 +61,7 @@ std::ostream& operator<<(std::ostream& out, cause c) {
         case cause::API: return out << "API";
         case cause::SCHEMA_CHANGE: return out << "SCHEMA_CHANGE";
         case cause::MIXED_CF: return out << "MIXED_CF";
+        case cause::SSTABLE_FORMAT_M: return out << "SSTABLE_FORMAT_M";
     }
     abort();
 }

unimplemented.hh

@@ -56,6 +56,7 @@ enum class cause {
     STORAGE_SERVICE,
     SCHEMA_CHANGE,
     MIXED_CF,
+    SSTABLE_FORMAT_M,
 };
 
 [[noreturn]] void fail(cause what);