PERF: Optimize Row construction and repeated cursor bookkeeping

mssql_python/connection.py

@@ -540,6 +540,7 @@ def __init__(
                 "ctype": ConstantsDDBC.SQL_WCHAR.value,
             },
         }
+        self._decoding_generation = 0
 
         # Auth type for acquiring fresh tokens at bulk copy time.
         # We intentionally do NOT cache the token — a fresh one is acquired
@@ -782,6 +783,7 @@ def _token_factory():
 
         # Initialize output converters dictionary and its lock for thread safety
         self._output_converters = {}
+        self._converters_generation = 0
         self._converters_lock = threading.Lock()
 
         # Initialize encoding/decoding settings lock for thread safety
@@ -1320,6 +1322,9 @@ def setdecoding(
         """
         Sets the text decoding used when reading SQL_CHAR and SQL_WCHAR from the database.
 
+        Existing cursors refresh their cached SQL_CHAR/SQL_WCHAR decoding settings
+        before their next fetch.
+
         This method configures how text data is decoded when reading from the database.
         In Python 3, all text is Unicode (str), so this primarily affects the encoding
         used to decode bytes from the database.
@@ -1443,6 +1448,7 @@ def setdecoding(
         # Store the decoding settings for the specified sqltype (thread-safe with lock)
         with self._encoding_lock:
             self._decoding_settings[sqltype] = {"encoding": encoding, "ctype": ctype}
+            self._decoding_generation += 1
 
         # Log with sanitized values for security
         sqltype_name = {
@@ -1647,6 +1653,8 @@ def add_output_converter(self, sqltype: Union[int, type], func: Callable[[Any],
 
         Thread-safe implementation that protects the converters dictionary with a lock.
 
+        Changes apply on the next fetch, including for an already executed result set.
+
         ⚠️ WARNING: Registering an output converter will cause the supplied Python function
         to be executed on every matching database value. Do not register converters from
         untrusted sources, as this can result in arbitrary code execution and security
@@ -1687,6 +1695,7 @@ def add_output_converter(self, sqltype: Union[int, type], func: Callable[[Any],
         """
         with self._converters_lock:
             self._output_converters[sqltype] = func
+            self._converters_generation += 1
             # Pass to the underlying connection if native implementation supports it
             if hasattr(self._conn, "add_output_converter"):
                 self._conn.add_output_converter(sqltype, func)
@@ -1717,6 +1726,8 @@ def remove_output_converter(self, sqltype: Union[int, type]) -> None:
 
         Thread-safe implementation that protects the converters dictionary with a lock.
 
+        Existing cursors use the updated converters on their next fetch.
+
         Args:
             sqltype (int or type): The SQL type value to remove the converter for
 
@@ -1726,6 +1737,7 @@ def remove_output_converter(self, sqltype: Union[int, type]) -> None:
         with self._converters_lock:
             if sqltype in self._output_converters:
                 del self._output_converters[sqltype]
+                self._converters_generation += 1
                 # Pass to the underlying connection if native implementation supports it
                 if hasattr(self._conn, "remove_output_converter"):
                     self._conn.remove_output_converter(sqltype)
@@ -1737,11 +1749,14 @@ def clear_output_converters(self) -> None:
 
         Thread-safe implementation that protects the converters dictionary with a lock.
 
+        Existing cursors stop applying converters on their next fetch.
+
         Returns:
             None
         """
         with self._converters_lock:
             self._output_converters.clear()
+            self._converters_generation += 1
             # Pass to the underlying connection if native implementation supports it
             if hasattr(self._conn, "clear_output_converters"):
                 self._conn.clear_output_converters()