db: Do not fail when creating a table with composite partition key

database.cc

@@ -63,7 +63,7 @@ schema::schema(sstring ks_name, sstring cf_name, std::vector<column> partition_k
         thrift.partition_key_type = partition_key[0].type;
     } else {
         // TODO: the type should be composite_type
-        throw std::runtime_error("not implemented");
+        warn(unimplemented::cause::LEGACY_COMPOSITE_KEYS);
     }
 
     build_columns(partition_key, column_definition::column_kind::PARTITION, _partition_key);

unimplemented.cc

@@ -25,6 +25,7 @@ std::ostream& operator<<(std::ostream& out, cause c) {
         case cause::COMPACT_TABLES: return out << "COMPACT_TABLES";
         case cause::GOSSIP: return out << "GOSSIP";
         case cause::TOKEN_RESTRICTION: return out << "TOKEN_RESTRICTION";
+        case cause::LEGACY_COMPOSITE_KEYS: return out << "LEGACY_COMPOSITE_KEYS";
     }
     assert(0);
 }

unimplemented.hh

@@ -24,6 +24,7 @@ enum class cause {
     COMPACT_TABLES,
     GOSSIP,
     TOKEN_RESTRICTION,
+    LEGACY_COMPOSITE_KEYS,
 };
 
 void fail(cause what) __attribute__((noreturn));