#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements. See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
"""Retry decorators for calls raising exceptions.
For internal use only; no backwards-compatibility guarantees.
This module is used mostly to decorate all integration points where the code
makes calls to remote services. Searching through the code base for @retry
should find all such places. For this reason even places where retry is not
needed right now use a @retry.no_retries decorator.
"""
import logging
import random
import sys
import time
import traceback
# Protect against environments where apitools library is not available.
# pylint: disable=wrong-import-order, wrong-import-position
# TODO(sourabhbajaj): Remove the GCP specific error code to a submodule
try:
from apitools.base.py.exceptions import HttpError
except ImportError:
HttpError = None
# pylint: enable=wrong-import-order, wrong-import-position
[docs]class PermanentException(Exception):
"""Base class for exceptions that should not be retried."""
pass
[docs]class FuzzedExponentialIntervals(object):
"""Iterable for intervals that are exponentially spaced, with fuzzing.
On iteration, yields retry interval lengths, in seconds. Every iteration over
this iterable will yield differently fuzzed interval lengths, as long as fuzz
is nonzero.
Args:
initial_delay_secs: The delay before the first retry, in seconds.
num_retries: The total number of times to retry.
factor: The exponential factor to use on subsequent retries.
Default is 2 (doubling).
fuzz: A value between 0 and 1, indicating the fraction of fuzz. For a
given delay d, the fuzzed delay is randomly chosen between
[(1 - fuzz) * d, d].
max_delay_secs: Maximum delay (in seconds). After this limit is reached,
further tries use max_delay_sec instead of exponentially increasing
the time. Defaults to 1 hour.
"""
def __init__(self, initial_delay_secs, num_retries, factor=2, fuzz=0.5,
max_delay_secs=60 * 60 * 1):
self._initial_delay_secs = initial_delay_secs
self._num_retries = num_retries
self._factor = factor
if not 0 <= fuzz <= 1:
raise ValueError('Fuzz parameter expected to be in [0, 1] range.')
self._fuzz = fuzz
self._max_delay_secs = max_delay_secs
def __iter__(self):
current_delay_secs = min(self._max_delay_secs, self._initial_delay_secs)
for _ in xrange(self._num_retries):
fuzz_multiplier = 1 - self._fuzz + random.random() * self._fuzz
yield current_delay_secs * fuzz_multiplier
current_delay_secs = min(
self._max_delay_secs, current_delay_secs * self._factor)
[docs]def retry_on_server_errors_filter(exception):
"""Filter allowing retries on server errors and non-HttpErrors."""
if (HttpError is not None) and isinstance(exception, HttpError):
return exception.status_code >= 500
return not isinstance(exception, PermanentException)
[docs]def retry_on_server_errors_and_timeout_filter(exception):
if HttpError is not None and isinstance(exception, HttpError):
if exception.status_code == 408: # 408 Request Timeout
return True
return retry_on_server_errors_filter(exception)
SERVER_ERROR_OR_TIMEOUT_CODES = [408, 500, 502, 503, 504, 598, 599]
[docs]class Clock(object):
"""A simple clock implementing sleep()."""
[docs] def sleep(self, value):
time.sleep(value)
[docs]def no_retries(fun):
"""A retry decorator for places where we do not want retries."""
return with_exponential_backoff(
retry_filter=lambda _: False, clock=None)(fun)
[docs]def with_exponential_backoff(
num_retries=7, initial_delay_secs=5.0, logger=logging.warning,
retry_filter=retry_on_server_errors_filter,
clock=Clock(), fuzz=True, factor=2, max_delay_secs=60 * 60):
"""Decorator with arguments that control the retry logic.
Args:
num_retries: The total number of times to retry.
initial_delay_secs: The delay before the first retry, in seconds.
logger: A callable used to report an exception. Must have the same signature
as functions in the standard logging module. The default is
logging.warning.
retry_filter: A callable getting the exception raised and returning True
if the retry should happen. For instance we do not want to retry on
404 Http errors most of the time. The default value will return true
for server errors (HTTP status code >= 500) and non Http errors.
clock: A clock object implementing a sleep method. The default clock will
use time.sleep().
fuzz: True if the delay should be fuzzed (default). During testing False
can be used so that the delays are not randomized.
factor: The exponential factor to use on subsequent retries.
Default is 2 (doubling).
max_delay_secs: Maximum delay (in seconds). After this limit is reached,
further tries use max_delay_sec instead of exponentially increasing
the time. Defaults to 1 hour.
Returns:
As per Python decorators with arguments pattern returns a decorator
for the function which in turn will return the wrapped (decorated) function.
The decorator is intended to be used on callables that make HTTP or RPC
requests that can temporarily timeout or have transient errors. For instance
the make_http_request() call below will be retried 16 times with exponential
backoff and fuzzing of the delay interval (default settings).
from apache_beam.utils import retry
# ...
@retry.with_exponential_backoff()
make_http_request(args)
"""
def real_decorator(fun):
"""The real decorator whose purpose is to return the wrapped function."""
def wrapper(*args, **kwargs):
retry_intervals = iter(
FuzzedExponentialIntervals(
initial_delay_secs, num_retries, factor,
fuzz=0.5 if fuzz else 0, max_delay_secs=max_delay_secs))
while True:
try:
return fun(*args, **kwargs)
except Exception as exn: # pylint: disable=broad-except
if not retry_filter(exn):
raise
# Get the traceback object for the current exception. The
# sys.exc_info() function returns a tuple with three elements:
# exception type, exception value, and exception traceback.
exn_traceback = sys.exc_info()[2]
try:
try:
sleep_interval = retry_intervals.next()
except StopIteration:
# Re-raise the original exception since we finished the retries.
raise exn, None, exn_traceback # pylint: disable=raising-bad-type
logger(
'Retry with exponential backoff: waiting for %s seconds before '
'retrying %s because we caught exception: %s '
'Traceback for above exception (most recent call last):\n%s',
sleep_interval,
getattr(fun, '__name__', str(fun)),
''.join(traceback.format_exception_only(exn.__class__, exn)),
''.join(traceback.format_tb(exn_traceback)))
clock.sleep(sleep_interval)
finally:
# Traceback objects in locals can cause reference cycles that will
# prevent garbage collection. Clear it now since we do not need
# it anymore.
sys.exc_clear()
exn_traceback = None
return wrapper
return real_decorator