api: extend connect with fetch_schema param

Added support of the fetch_schema parameter,
which allows to ignore schema changes on the server.

Closes #219

Author: GRISHNOV

tarantool/connection.py

@@ -363,7 +363,8 @@ def __init__(self, host, port,
                  ssl_ca_file=DEFAULT_SSL_CA_FILE,
                  ssl_ciphers=DEFAULT_SSL_CIPHERS,
                  packer_factory=default_packer_factory,
-                 unpacker_factory=default_unpacker_factory):
+                 unpacker_factory=default_unpacker_factory,
+                 fetch_schema = True):
         """
         :param host: Server hostname or IP address. Use ``None`` for
             Unix sockets.
@@ -533,8 +534,10 @@ def __init__(self, host, port,
         self.socket_timeout = socket_timeout
         self.reconnect_delay = reconnect_delay
         self.reconnect_max_attempts = reconnect_max_attempts
-        self.schema = Schema(self)
-        self.schema_version = 1
+        self.fetch_schema = fetch_schema
+        if self.fetch_schema:
+            self.schema = Schema(self)
+            self.schema_version = 1
         self._socket = None
         self.connected = False
         self.error = True
@@ -745,7 +748,8 @@ def connect(self):
             if self.transport == SSL_TRANSPORT:
                 self.wrap_socket_ssl()
             self.handshake()
-            self.load_schema()
+            if self.fetch_schema:
+                self.load_schema()
             self._check_features()
         except SslError as e:
             raise e
@@ -841,7 +845,8 @@ def _send_request_wo_reconnect(self, request, on_push=None, on_push_ctx=None):
                 response = request.response_class(self, self._read_response())
                 break
             except SchemaReloadException as e:
-                self.update_schema(e.schema_version)
+                if self.fetch_schema:
+                    self.update_schema(e.schema_version)
                 continue
 
         while response._code == IPROTO_CHUNK:

tarantool/request.py

@@ -186,9 +186,13 @@ def header(self, length):
         """
 
         self._sync = self.conn.generate_sync()
-        header = self._dumps({IPROTO_REQUEST_TYPE: self.request_type,
-                              IPROTO_SYNC: self._sync,
-                              IPROTO_SCHEMA_ID: self.conn.schema_version})
+        header_fields = {
+            IPROTO_REQUEST_TYPE: self.request_type,
+            IPROTO_SYNC: self._sync,
+        }
+        if self.conn.fetch_schema:
+            header_fields[IPROTO_SCHEMA_ID] = self.conn.schema_version
+        header = self._dumps(header_fields)
 
         return self._dumps(length + len(header)) + header