Retry serialization failures only once

The refresh only writes once per rollover, so once the request that won
the race has committed, a retry has nothing left to conflict with. If
that single retry still fails, something else is wrong and it's better
to surface the error than to keep rerunning the whole view.

Author: FennemAI

pgcommitfest/commitfest/tests/test_retry_on_serialization_failure.py

@@ -18,9 +18,9 @@ def _pg_error(pgcode):
 @pytest.mark.parametrize(
     "pgcode,failures,expected_calls",
     [
-        ("40001", 2, 3),  # serialization failure, recovers
+        ("40001", 1, 2),  # serialization failure, recovers
         ("40P01", 1, 2),  # deadlock, recovers
-        ("40001", 99, 5),  # persistent failure, gives up after 5 attempts
+        ("40001", 99, 2),  # persistent failure, gives up after one retry
         ("57014", 99, 1),  # query_canceled is not transient, no retry
     ],
 )

pgcommitfest/commitfest/views.py

@@ -77,19 +77,16 @@ def retry_on_serialization_failure(view_func):
 
     @functools.wraps(view_func)
     def wrapper(*args, **kwargs):
-        # A handful of attempts is plenty: the refresh only writes once per
-        # rollover, so after the first one commits there is nothing left to
-        # conflict with.
-        last_attempt = 4
-        for attempt in range(last_attempt + 1):
-            try:
-                return view_func(*args, **kwargs)
-            except OperationalError as e:
-                if (
-                    attempt == last_attempt
-                    or getattr(e.__cause__, "pgcode", None) not in RETRYABLE_PGCODES
-                ):
-                    raise
+        try:
+            return view_func(*args, **kwargs)
+        except OperationalError as e:
+            if getattr(e.__cause__, "pgcode", None) not in RETRYABLE_PGCODES:
+                raise
+        # A single retry is enough: the refresh only writes once per rollover,
+        # so after the winning request commits there is nothing left to
+        # conflict with. If the retry fails anyway, something else is going on
+        # and we'd rather surface the error than keep hammering the database.
+        return view_func(*args, **kwargs)
 
     return wrapper