Performance improvement in Row

Various performance improvements to Row instanciation
- avoid passing processors if they are all None
- improve processor logic in cython
- improve tuplegetter using slices when contiguous indexes are used

Some timing follow.

In particular [base_]row_new_proc that tests using processors has
a 25% improvement compared to before in cython.
Looking at the [b]row_new_proc_none that test a list of processors
all None, this has 50% improvement in cython when passing the none list,
but in this patch it would usually be disabled by passing None, so the
performance gain is actually 90%, since it would run the case
[base_]row_new.

Tuplegetter is a bit faster in the single item get and when getting
sequential indexes (like indexes 1,2,3,4) at the cost of a bit
longer creation time in python, cython is mostly the same.

Current times
                    | python      | cython      | cy / py     |
base_row_new        | 0.639817400 | 0.118265500 | 0.184842582 |
row_new             | 0.680355100 | 0.129714600 | 0.190657202 |
base_row_new_proc   | 3.076538900 | 1.488428600 | 0.483799701 |
row_new_proc        | 3.119700100 | 1.532197500 | 0.491136151 |
brow_new_proc_none  | 1.917702300 | 0.475511500 | 0.247958977 |
row_new_proc_none   | 1.956253300 | 0.497803100 | 0.254467609 |

tuplegetter_one     | 0.152512600 | 0.148523900 | 0.973846751 |
tuplegetter_many    | 0.184394100 | 0.184511500 | 1.000636680 |
tuplegetter_seq     | 0.154832800 | 0.156270100 | 1.009282917 |
tuplegetter_new_one | 0.523730000 | 0.343402200 | 0.655685563 |
tuplegetter_new_many| 0.738924400 | 0.420961400 | 0.569694816 |
tuplegetter_new_seq | 1.062036900 | 0.495462000 | 0.466520514 |

Parent commit times
                    | python      | cython      | cy / py     |
base_row_new        | 0.643890800 | 0.113548300 | 0.176347138 |
row_new             | 0.674885900 | 0.124391800 | 0.184315304 |
base_row_new_proc   | 3.072020400 | 2.017367000 | 0.656690626 |
row_new_proc        | 3.109943400 | 2.048359400 | 0.658648450 |
brow_new_proc_none  | 1.967133700 | 1.006326000 | 0.511569702 |
row_new_proc_none   | 1.960814900 | 1.025217800 | 0.522852922 |

tuplegetter_one     | 0.197359900 | 0.205999000 | 1.043773330 |
tuplegetter_many    | 0.196575900 | 0.194888500 | 0.991416038 |
tuplegetter_seq     | 0.192723900 | 0.205635000 | 1.066992729 |
tuplegetter_new_one | 0.534644500 | 0.414311700 | 0.774929322 |
tuplegetter_new_many| 0.479376500 | 0.417448100 | 0.870814694 |
tuplegetter_new_seq | 0.481580200 | 0.412697900 | 0.856966088 |

Change-Id: I2ca1f49dca2beff625c283f1363c29c8ccc0c3f7

1 files changed, 26 insertions, 18 deletions

diff --git a/lib/sqlalchemy/engine/cursor.py b/lib/sqlalchemy/engine/cursor.py
index bd46f30ac..7491afc3e 100644
--- a/lib/sqlalchemy/engine/cursor.py
+++ b/lib/sqlalchemy/engine/cursor.py
@@ -14,6 +14,7 @@ from __future__ import annotations
 
 import collections
 import functools
+import operator
 import typing
 from typing import Any
 from typing import cast
@@ -1440,39 +1441,46 @@ class CursorResult(Result[_T]):
             # getter assuming no transformations will be called as this
             # is the most common case
 
-            if echo:
-                log = self.context.connection._log_debug
-
-                def _log_row(row):
-                    log("Row %r", sql_util._repr_row(row))
-                    return row
-
-                self._row_logging_fn = log_row = _log_row
-            else:
-                log_row = None
-
             metadata = self._init_metadata(context, cursor_description)
 
             _make_row = functools.partial(
                 Row,
                 metadata,
-                metadata._processors,
+                metadata._effective_processors,
                 metadata._key_to_index,
             )
-            if log_row:
+
+            if context._num_sentinel_cols:
+                sentinel_filter = operator.itemgetter(
+                    slice(-context._num_sentinel_cols)
+                )
+
+                def _sliced_row(raw_data):
+                    return _make_row(sentinel_filter(raw_data))
+
+                sliced_row = _sliced_row
+            else:
+                sliced_row = _make_row
+
+            if echo:
+                log = self.context.connection._log_debug
+
+                def _log_row(row):
+                    log("Row %r", sql_util._repr_row(row))
+                    return row
+
+                self._row_logging_fn = _log_row
 
                 def _make_row_2(row):
-                    made_row = _make_row(row)
-                    assert log_row is not None
-                    log_row(made_row)
-                    return made_row
+                    return _log_row(sliced_row(row))
 
                 make_row = _make_row_2
             else:
-                make_row = _make_row
+                make_row = sliced_row
             self._set_memoized_attribute("_row_getter", make_row)
 
         else:
+            assert context._num_sentinel_cols == 0
             self._metadata = self._no_result_metadata
 
     def _init_metadata(self, context, cursor_description):