PYTHON-5562: Investigate default values for withTransaction backoff parameters

graph.py

@@ -0,0 +1,82 @@
+from __future__ import annotations
+
+import matplotlib.cm as mplcm
+import matplotlib.colors as colors
+import matplotlib.pyplot as plt
+import numpy as np
+
+threads = [1, 2, 4, 8, 16, 32, 64, 128, 256]
+
+data = {
+    "local_main": {
+        "avg": [[0.01], [0.03], [0.05], [0.09], [0.21], [0.38], [0.95], [4.05], [11.11]],
+        "p50": [[0.01], [0.02], [0.03], [0.05], [0.12], [0.25], [0.67], [3.22], [9.8]],
+        "p90": [[0.02], [0.05], [0.11], [0.23], [0.52], [0.94], [2.01], [8.88], [23.47]],
+        "p99": [[0.02], [0.05], [0.11], [0.23], [0.52], [0.94], [2.01], [8.88], [23.47]],
+        "p100": [[0.04], [0.21], [0.3], [0.58], [1.22], [2.59], [7.25], [17.03], [25.38]],
+    },
+    "local_original_1.5": {
+        "avg": [[0.01], [0.02], [0.04], [0.09], [0.2], [0.35], [0.65], [1.14], [2.21]],
+        "p50": [[0.01], [0.01], [0.01], [0.02], [0.06], [0.09], [0.2], [0.45], [1.91]],
+        "p90": [[0.02], [0.04], [0.11], [0.22], [0.49], [0.81], [1.87], [3.72], [4.76]],
+        "p99": [[0.02], [0.04], [0.11], [0.22], [0.49], [0.81], [1.87], [3.72], [4.76]],
+        "p100": [[0.04], [0.62], [1.11], [3.33], [4.71], [6.07], [5.64], [6.05], [6.76]],
+    },
+    "local_original_2": {
+        "avg": [[0.01], [0.02], [0.04], [0.09], [0.18], [0.39], [0.63], [1.23], [2.28]],
+        "p50": [[0.01], [0.01], [0.01], [0.02], [0.02], [0.06], [0.17], [0.41], [1.9]],
+        "p90": [[0.01], [0.02], [0.08], [0.21], [0.33], [1.24], [1.83], [3.82], [4.91]],
+        "p99": [[0.01], [0.02], [0.08], [0.21], [0.33], [1.24], [1.83], [3.82], [4.91]],
+        "p100": [[0.04], [1.3], [1.54], [3.07], [3.72], [5.55], [5.44], [6.42], [7.06]],
+    },
+    "local_server_algo": {
+        "avg": [[0.01], [0.02], [0.05], [0.1], [0.19], [0.36], [0.73], [1.23], [2.19]],
+        "p50": [[0.01], [0.01], [0.01], [0.01], [0.03], [0.09], [0.19], [0.59], [2.04]],
+        "p90": [[0.02], [0.04], [0.1], [0.22], [0.51], [1.07], [2.37], [3.58], [4.74]],
+        "p99": [[0.02], [0.04], [0.1], [0.22], [0.51], [1.07], [2.37], [3.58], [4.74]],
+        "p100": [[0.09], [0.65], [1.35], [2.87], [3.31], [4.4], [6.55], [5.84], [6.88]],
+    },
+}
+
+
+metrics = ["avg", "p90", "p100"]
+metric_titles = {
+    "avg": "Average Latency",
+    "p50": "p50 Latency",
+    "p90": "p90 Latency",
+    "p99": "p99 Latency",
+    "p100": "p100 (Max) Latency",
+}
+
+plt.figure(figsize=(16, 4 * len(metrics)))
+NUM_COLORS = len(data.keys()) + 1
+cm = plt.get_cmap("gist_rainbow")
+cNorm = colors.Normalize(vmin=0, vmax=NUM_COLORS - 1)
+scalarMap = mplcm.ScalarMappable(norm=cNorm, cmap=cm)
+for i, metric in enumerate(metrics, 1):
+    if metric in ["avg"]:
+        ax = plt.subplot(len(metrics), 2, i)
+    else:
+        ax = plt.subplot(len(metrics), 2, (i - 1) * (2) + 1)
+    ax.set_prop_cycle(color=[scalarMap.to_rgba(i) for i in range(NUM_COLORS)])
+    order = []
+    for label, vals in data.items():
+        if metric not in vals:
+            continue
+        arr = np.concatenate(np.around(np.array(vals[metric]), decimals=2))
+        order.append(plt.plot(threads, arr, "o-", label=label))
+
+    plt.title(metric_titles[metric])
+    plt.xscale("log", base=2)
+    plt.xlabel("Threads")
+    plt.ylabel("Seconds")
+    plt.xticks(threads, threads)
+    plt.grid(True, which="both", axis="x", linestyle="--", alpha=0.5)
+    plt.axhline(y=0, color="gray", linestyle="-")
+    if metric != "p90":
+        plt.legend().set_visible(False)
+    else:
+        plt.legend(loc=(1.01, 0.5), fontsize=8)
+
+plt.tight_layout()
+plt.show()

pymongo/asynchronous/client_session.py

@@ -473,15 +473,25 @@ def _max_time_expired_error(exc: PyMongoError) -> bool:
 # This limit is non-configurable and was chosen to be twice the 60 second
 # default value of MongoDB's `transactionLifetimeLimitSeconds` parameter.
 _WITH_TRANSACTION_RETRY_TIME_LIMIT = 120
-_BACKOFF_MAX = 1
-_BACKOFF_INITIAL = 0.050  # 50ms initial backoff
+_BACKOFF_MAX = 0.500  # 500ms max backoff
+_BACKOFF_INITIAL = 0.001  # 1ms initial backoff
+
+
+def _set_backoff_initial(seconds: float) -> None:
+    global _BACKOFF_INITIAL  # noqa: PLW0603
+    _BACKOFF_INITIAL = seconds
 
 
 def _within_time_limit(start_time: float) -> bool:
     """Are we within the with_transaction retry limit?"""
     return time.monotonic() - start_time < _WITH_TRANSACTION_RETRY_TIME_LIMIT
 
 
+def _would_exceed_time_limit(start_time: float, backoff: float) -> bool:
+    """Is the backoff within the with_transaction retry limit?"""
+    return time.monotonic() + backoff - start_time >= _WITH_TRANSACTION_RETRY_TIME_LIMIT
+
+
 _T = TypeVar("_T")
 
 if TYPE_CHECKING:
@@ -705,10 +715,14 @@ async def callback(session, custom_arg, custom_kwarg=None):
         """
         start_time = time.monotonic()
         retry = 0
+        last_error: Optional[BaseException] = None
         while True:
             if retry:  # Implement exponential backoff on retry.
                 jitter = random.random()  # noqa: S311
-                backoff = jitter * min(_BACKOFF_INITIAL * (2**retry), _BACKOFF_MAX)
+                backoff = jitter * min(_BACKOFF_INITIAL * (1.25**retry), _BACKOFF_MAX)
+                if _would_exceed_time_limit(start_time, backoff):
+                    assert last_error is not None
+                    raise last_error
                 await asyncio.sleep(backoff)
             retry += 1
             await self.start_transaction(
@@ -718,6 +732,7 @@ async def callback(session, custom_arg, custom_kwarg=None):
                 ret = await callback(self)
             # Catch KeyboardInterrupt, CancelledError, etc. and cleanup.
             except BaseException as exc:
+                last_error = exc
                 if self.in_transaction:
                     await self.abort_transaction()
                 if (

pymongo/synchronous/client_session.py

@@ -471,15 +471,25 @@ def _max_time_expired_error(exc: PyMongoError) -> bool:
 # This limit is non-configurable and was chosen to be twice the 60 second
 # default value of MongoDB's `transactionLifetimeLimitSeconds` parameter.
 _WITH_TRANSACTION_RETRY_TIME_LIMIT = 120
-_BACKOFF_MAX = 1
-_BACKOFF_INITIAL = 0.050  # 50ms initial backoff
+_BACKOFF_MAX = 0.500  # 500ms max backoff
+_BACKOFF_INITIAL = 0.001  # 1ms initial backoff
+
+
+def _set_backoff_initial(seconds: float) -> None:
+    global _BACKOFF_INITIAL  # noqa: PLW0603
+    _BACKOFF_INITIAL = seconds
 
 
 def _within_time_limit(start_time: float) -> bool:
     """Are we within the with_transaction retry limit?"""
     return time.monotonic() - start_time < _WITH_TRANSACTION_RETRY_TIME_LIMIT
 
 
+def _would_exceed_time_limit(start_time: float, backoff: float) -> bool:
+    """Is the backoff within the with_transaction retry limit?"""
+    return time.monotonic() + backoff - start_time >= _WITH_TRANSACTION_RETRY_TIME_LIMIT
+
+
 _T = TypeVar("_T")
 
 if TYPE_CHECKING:
@@ -703,17 +713,22 @@ def callback(session, custom_arg, custom_kwarg=None):
         """
         start_time = time.monotonic()
         retry = 0
+        last_error: Optional[BaseException] = None
         while True:
             if retry:  # Implement exponential backoff on retry.
                 jitter = random.random()  # noqa: S311
-                backoff = jitter * min(_BACKOFF_INITIAL * (2**retry), _BACKOFF_MAX)
+                backoff = jitter * min(_BACKOFF_INITIAL * (1.25**retry), _BACKOFF_MAX)
+                if _would_exceed_time_limit(start_time, backoff):
+                    assert last_error is not None
+                    raise last_error
                 time.sleep(backoff)
             retry += 1
             self.start_transaction(read_concern, write_concern, read_preference, max_commit_time_ms)
             try:
                 ret = callback(self)
             # Catch KeyboardInterrupt, CancelledError, etc. and cleanup.
             except BaseException as exc:
+                last_error = exc
                 if self.in_transaction:
                     self.abort_transaction()
                 if (

summarize.py

@@ -0,0 +1,65 @@
+from __future__ import annotations
+
+import csv
+import pprint
+import re
+from collections import defaultdict
+
+
+def testing_n_threads(f_in, data):
+    threads = re.match(r"Testing (?P<n_threads>.*) threads", f_in.readline()).group("n_threads")
+    seconds = re.match(
+        r"All threads completed after (?P<n_seconds>.*) seconds", f_in.readline()
+    ).group("n_seconds")
+    tries = re.match(r"Total number of retry attempts: (?P<n_tries>.*)", f_in.readline()).group(
+        "n_tries"
+    )
+    data[f"{threads}_sec"].append(float(seconds))
+    data[f"{threads}_try"].append(int(tries))
+    return data
+
+
+def read_table(f_in, data):
+    # Initialize the CSV reader with the pipe '|' as the delimiter
+    reader = csv.reader(f_in, delimiter="|")
+    next(reader)  # skip header
+
+    for row in reader:
+        if "threads " in row:
+            continue
+        row = [col.strip() for col in row]  # noqa:PLW2901
+        if row == []:
+            continue
+        # Convert numbers to appropriate types (int for threads, float for statistics)
+        threads = int(row[0])
+        avg, p50, p90, p99, p100 = map(float, row[1:])
+        # Append the parsed row to the list
+        data[f"{threads}_avg"].append(avg)
+        data[f"{threads}_p50"].append(p50)
+        data[f"{threads}_p90"].append(p90)
+        data[f"{threads}_p99"].append(p99)
+        data[f"{threads}_p100"].append(p100)
+    return data
+
+
+path = "/Users/iris.ho/Github/backpressure/final"
+files = ["main", "local_original_1.5", "local_original_2", "local_server_algo"]
+print_data = {}
+pp = pprint.PrettyPrinter(width=80)
+THREADS = [1, 2, 4, 8, 16, 32, 64, 128, 256]
+for f in files:
+    data = defaultdict(list)
+    with open(f"{path}/{f}.txt") as f_in:
+        for _ in THREADS:
+            data = testing_n_threads(f_in, data)
+            f_in.readline()
+        f_in.readline()
+        data = read_table(f_in, data)
+    print_data[f] = {
+        "avg": [data[f"{thread}_avg"] for thread in THREADS],
+        "p50": [data[f"{thread}_p50"] for thread in THREADS],
+        "p90": [data[f"{thread}_p90"] for thread in THREADS],
+        "p99": [data[f"{thread}_p99"] for thread in THREADS],
+        "p100": [data[f"{thread}_p100"] for thread in THREADS],
+    }
+print(print_data)  # noqa: T201

test/asynchronous/test_transactions.py

@@ -15,7 +15,9 @@
 """Execute Transactions Spec tests."""
 from __future__ import annotations
 
+import random
 import sys
+import time
 from io import BytesIO
 from test.asynchronous.utils_spec_runner import AsyncSpecRunner
 
@@ -36,7 +38,11 @@
 from bson.raw_bson import RawBSONDocument
 from pymongo import WriteConcern, _csot
 from pymongo.asynchronous import client_session
-from pymongo.asynchronous.client_session import TransactionOptions
+from pymongo.asynchronous.client_session import (
+    _BACKOFF_MAX,
+    TransactionOptions,
+    _set_backoff_initial,
+)
 from pymongo.asynchronous.command_cursor import AsyncCommandCursor
 from pymongo.asynchronous.cursor import AsyncCursor
 from pymongo.asynchronous.helpers import anext
@@ -602,6 +608,81 @@ async def callback(session):
             await s.with_transaction(callback)
             self.assertFalse(s.in_transaction)
 
+    @async_client_context.require_test_commands
+    @async_client_context.require_transactions
+    async def test_transaction_backoff_is_random(self):
+        client = async_client_context.client
+        coll = client[self.db.name].test
+        # set fail point to trigger transaction failure and trigger backoff
+        await self.set_fail_point(
+            {
+                "configureFailPoint": "failCommand",
+                "mode": {
+                    "times": 30
+                },  # sufficiently high enough such that the time effect of backoff is noticeable
+                "data": {
+                    "failCommands": ["commitTransaction"],
+                    "errorCode": 24,
+                },
+            }
+        )
+        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.assertLess(end - start, 5)  # sum of backoffs is ~3.5 seconds
+
+    @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
+
+        random.random = always_one
+        # set fail point to trigger transaction failure and trigger backoff
+        await self.set_fail_point(
+            {
+                "configureFailPoint": "failCommand",
+                "mode": {
+                    "times": 30
+                },  # sufficiently high enough such that the time effect of backoff is noticeable
+                "data": {
+                    "failCommands": ["commitTransaction"],
+                    "errorCode": 24,
+                },
+            }
+        )
+        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 backoffs is 3.5629515313825695
+
+        random.random = _original_random_random
+
 
 class TestOptionsInsideTransactionProse(AsyncTransactionsBase):
     @async_client_context.require_transactions