fix backoff constants and test

Author: sleepyStick

pymongo/asynchronous/client_session.py

@@ -473,7 +473,7 @@ def _max_time_expired_error(exc: PyMongoError) -> bool:
 # default value of MongoDB's `transactionLifetimeLimitSeconds` parameter.
 _WITH_TRANSACTION_RETRY_TIME_LIMIT = 120
 _BACKOFF_MAX = 0.500  # 500ms max backoff
-_BACKOFF_INITIAL = 0.001  # 1ms initial backoff
+_BACKOFF_INITIAL = 0.005  # 5ms initial backoff
 
 
 def _within_time_limit(start_time: float) -> bool:
@@ -717,7 +717,7 @@ async def callback(session, custom_arg, custom_kwarg=None):
         while True:
             if retry:  # Implement exponential backoff on retry.
                 jitter = random.random()  # noqa: S311
-                backoff = jitter * min(_BACKOFF_INITIAL * (1.25**retry), _BACKOFF_MAX)
+                backoff = jitter * min(_BACKOFF_INITIAL * (1.5**retry), _BACKOFF_MAX)
                 if _would_exceed_time_limit(start_time, backoff):
                     assert last_error is not None
                     raise last_error

pymongo/synchronous/client_session.py

@@ -471,7 +471,7 @@ def _max_time_expired_error(exc: PyMongoError) -> bool:
 # default value of MongoDB's `transactionLifetimeLimitSeconds` parameter.
 _WITH_TRANSACTION_RETRY_TIME_LIMIT = 120
 _BACKOFF_MAX = 0.500  # 500ms max backoff
-_BACKOFF_INITIAL = 0.001  # 1ms initial backoff
+_BACKOFF_INITIAL = 0.005  # 5ms initial backoff
 
 
 def _within_time_limit(start_time: float) -> bool:
@@ -715,7 +715,7 @@ def callback(session, custom_arg, custom_kwarg=None):
         while True:
             if retry:  # Implement exponential backoff on retry.
                 jitter = random.random()  # noqa: S311
-                backoff = jitter * min(_BACKOFF_INITIAL * (1.25**retry), _BACKOFF_MAX)
+                backoff = jitter * min(_BACKOFF_INITIAL * (1.5**retry), _BACKOFF_MAX)
                 if _would_exceed_time_limit(start_time, backoff):
                     assert last_error is not None
                     raise last_error

test/asynchronous/test_transactions.py

@@ -622,15 +622,25 @@ async def callback(session):
 
     @async_client_context.require_test_commands
     @async_client_context.require_transactions
-    async def test_transaction_backoff_is_random(self):
+    async def test_transaction_backoff(self):
         client = async_client_context.client
         coll = client[self.db.name].test
+        # patch random to make it deterministic
+        _original_random_random = random.random
+
+        def always_one():
+            return 1
+
+        def always_zero():
+            return 0
+
+        random.random = always_zero
         # set fail point to trigger transaction failure and trigger backoff
         await self.set_fail_point(
             {
                 "configureFailPoint": "failCommand",
                 "mode": {
-                    "times": 30
+                    "times": 13
                 },  # sufficiently high enough such that the time effect of backoff is noticeable
                 "data": {
                     "failCommands": ["commitTransaction"],
@@ -642,35 +652,22 @@ async def test_transaction_backoff_is_random(self):
             self.set_fail_point, {"configureFailPoint": "failCommand", "mode": "off"}
         )
 
-        start = time.monotonic()
-
         async def callback(session):
             await coll.insert_one({}, session=session)
 
+        start = time.monotonic()
         async with self.client.start_session() as s:
             await s.with_transaction(callback)
-
         end = time.monotonic()
-        self.assertLess(end - start, 3.5)  # sum of 30 backoffs are 3.5629515313825695
-
-    @async_client_context.require_test_commands
-    @async_client_context.require_transactions
-    async def test_transaction_backoff(self):
-        client = async_client_context.client
-        coll = client[self.db.name].test
-        # patch random to make it deterministic
-        _original_random_random = random.random
-
-        def always_one():
-            return 1
+        no_backoff_time = end - start
 
         random.random = always_one
         # set fail point to trigger transaction failure and trigger backoff
         await self.set_fail_point(
             {
                 "configureFailPoint": "failCommand",
                 "mode": {
-                    "times": 30
+                    "times": 13
                 },  # sufficiently high enough such that the time effect of backoff is noticeable
                 "data": {
                     "failCommands": ["commitTransaction"],
@@ -681,17 +678,11 @@ def always_one():
         self.addAsyncCleanup(
             self.set_fail_point, {"configureFailPoint": "failCommand", "mode": "off"}
         )
-
         start = time.monotonic()
-
-        async def callback(session):
-            await coll.insert_one({}, session=session)
-
         async with self.client.start_session() as s:
             await s.with_transaction(callback)
-
         end = time.monotonic()
-        self.assertGreaterEqual(end - start, 3.5)  # sum of 30 backoffs are 3.5629515313825695
+        self.assertLess(abs(end - start - (no_backoff_time + 2.2)), 1)  # sum of 13 backoffs is 2.2
 
         random.random = _original_random_random
 

test/test_transactions.py

@@ -610,15 +610,25 @@ def callback(session):
 
     @client_context.require_test_commands
     @client_context.require_transactions
-    def test_transaction_backoff_is_random(self):
+    def test_transaction_backoff(self):
         client = client_context.client
         coll = client[self.db.name].test
+        # patch random to make it deterministic
+        _original_random_random = random.random
+
+        def always_one():
+            return 1
+
+        def always_zero():
+            return 0
+
+        random.random = always_zero
         # set fail point to trigger transaction failure and trigger backoff
         self.set_fail_point(
             {
                 "configureFailPoint": "failCommand",
                 "mode": {
-                    "times": 30
+                    "times": 13
                 },  # sufficiently high enough such that the time effect of backoff is noticeable
                 "data": {
                     "failCommands": ["commitTransaction"],
@@ -628,35 +638,22 @@ def test_transaction_backoff_is_random(self):
         )
         self.addCleanup(self.set_fail_point, {"configureFailPoint": "failCommand", "mode": "off"})
 
-        start = time.monotonic()
-
         def callback(session):
             coll.insert_one({}, session=session)
 
+        start = time.monotonic()
         with self.client.start_session() as s:
             s.with_transaction(callback)
-
         end = time.monotonic()
-        self.assertLess(end - start, 3.5)  # sum of 30 backoffs are 3.5629515313825695
-
-    @client_context.require_test_commands
-    @client_context.require_transactions
-    def test_transaction_backoff(self):
-        client = client_context.client
-        coll = client[self.db.name].test
-        # patch random to make it deterministic
-        _original_random_random = random.random
-
-        def always_one():
-            return 1
+        no_backoff_time = end - start
 
         random.random = always_one
         # set fail point to trigger transaction failure and trigger backoff
         self.set_fail_point(
             {
                 "configureFailPoint": "failCommand",
                 "mode": {
-                    "times": 30
+                    "times": 13
                 },  # sufficiently high enough such that the time effect of backoff is noticeable
                 "data": {
                     "failCommands": ["commitTransaction"],
@@ -665,17 +662,11 @@ def always_one():
             }
         )
         self.addCleanup(self.set_fail_point, {"configureFailPoint": "failCommand", "mode": "off"})
-
         start = time.monotonic()
-
-        def callback(session):
-            coll.insert_one({}, session=session)
-
         with self.client.start_session() as s:
             s.with_transaction(callback)
-
         end = time.monotonic()
-        self.assertGreaterEqual(end - start, 3.5)  # sum of 30 backoffs are 3.5629515313825695
+        self.assertLess(abs(end - start - (no_backoff_time + 2.2)), 1)  # sum of 13 backoffs is 2.2
 
         random.random = _original_random_random