Retry attempts that fail due to a connection timeout (databricks#24)

* Isolate delay bounding logic
* Move error details scope up one-level.
* Retry GetOperationStatus if an OSError was raised during execution. Add retry_delay_default to use in this case.
* Log when a request is retried due to an OSError. Emit warnings for unexpected OSError codes
* Update docstring for make_request
* Nit: unit tests show the .warn message is deprecated. DeprecationWarning: The 'warn' function is deprecated, use 'warning' instead

Signed-off-by: Jesse Whitehouse <[email protected]>

Author: Jesse

src/databricks/sql/thrift_backend.py

@@ -1,4 +1,5 @@
 from decimal import Decimal
+import errno
 import logging
 import math
 import time
@@ -15,6 +16,9 @@
 
 from databricks.sql.thrift_api.TCLIService import TCLIService, ttypes
 from databricks.sql import *
+from databricks.sql.thrift_api.TCLIService.TCLIService import (
+    Client as TCLIServiceClient,
+)
 from databricks.sql.utils import (
     ArrowQueue,
     ExecuteResponse,
@@ -39,6 +43,7 @@
     "_retry_delay_max": (float, 60, 5, 3600),
     "_retry_stop_after_attempts_count": (int, 30, 1, 60),
     "_retry_stop_after_attempts_duration": (float, 900, 1, 86400),
+    "_retry_delay_default": (float, 5, 1, 60),
 }
 
 
@@ -71,6 +76,8 @@ def __init__(
         # _retry_delay_min                      (default: 1)
         # _retry_delay_max                      (default: 60)
         #   {min,max} pre-retry delay bounds
+        # _retry_delay_default                   (default: 5)
+        #   Only used when GetOperationStatus fails due to a TCP/OS Error.
         # _retry_stop_after_attempts_count      (default: 30)
         #   total max attempts during retry sequence
         # _retry_stop_after_attempts_duration   (default: 900)
@@ -158,7 +165,7 @@ def _initialize_retry_args(self, kwargs):
                 "retry parameter: {} given_or_default {}".format(key, given_or_default)
             )
             if bound != given_or_default:
-                logger.warn(
+                logger.warning(
                     "Override out of policy retry parameter: "
                     + "{} given {}, restricted to {}".format(
                         key, given_or_default, bound
@@ -243,7 +250,9 @@ def _handle_request_error(self, error_info, attempt, elapsed):
     # FUTURE: Consider moving to https://github.com/litl/backoff or
     # https://github.com/jd/tenacity for retry logic.
     def make_request(self, method, request):
-        """Execute given request, attempting retries when receiving HTTP 429/503.
+        """Execute given request, attempting retries when
+            1. Receiving HTTP 429/503 from server
+            2. OSError is raised during a GetOperationStatus
 
         For delay between attempts, honor the given Retry-After header, but with bounds.
         Use lower bound of expontial-backoff based on _retry_delay_min,
@@ -260,17 +269,21 @@ def make_request(self, method, request):
         def get_elapsed():
             return time.time() - t0
 
+        def bound_retry_delay(attempt, proposed_delay):
+            """bound delay (seconds) by [min_delay*1.5^(attempt-1), max_delay]"""
+            delay = int(proposed_delay)
+            delay = max(delay, self._retry_delay_min * math.pow(1.5, attempt - 1))
+            delay = min(delay, self._retry_delay_max)
+            return delay
+
         def extract_retry_delay(attempt):
             # encapsulate retry checks, returns None || delay-in-secs
             # Retry IFF 429/503 code + Retry-After header set
             http_code = getattr(self._transport, "code", None)
             retry_after = getattr(self._transport, "headers", {}).get("Retry-After")
             if http_code in [429, 503] and retry_after:
                 # bound delay (seconds) by [min_delay*1.5^(attempt-1), max_delay]
-                delay = int(retry_after)
-                delay = max(delay, self._retry_delay_min * math.pow(1.5, attempt - 1))
-                delay = min(delay, self._retry_delay_max)
-                return delay
+                return bound_retry_delay(attempt, int(retry_after))
             return None
 
         def attempt_request(attempt):
@@ -279,24 +292,57 @@ def attempt_request(attempt):
             # - non-None method_return -> success, return and be done
             # - non-None retry_delay -> sleep delay before retry
             # - error, error_message always set when available
+
+            error, error_message, retry_delay = None, None, None
             try:
                 logger.debug("Sending request: {}".format(request))
                 response = method(request)
                 logger.debug("Received response: {}".format(response))
                 return response
-            except Exception as error:
+            except OSError as err:
+                error = err
+                error_message = str(err)
+
+                gos_name = TCLIServiceClient.GetOperationStatus.__name__
+                if method.__name__ == gos_name:
+                    retry_delay = bound_retry_delay(attempt, self._retry_delay_default)
+
+                    # fmt: off
+                    # The built-in errno package encapsulates OSError codes, which are OS-specific.
+                    # log.info for errors we believe are not unusual or unexpected. log.warn for
+                    # for others like EEXIST, EBADF, ERANGE which are not expected in this context.
+                    #
+                    # I manually tested this retry behaviour using mitmweb and confirmed that 
+                    # GetOperationStatus requests are retried when I forced network connection
+                    # interruptions / timeouts / reconnects. See #24 for more info.
+                                            # | Debian | Darwin |
+                    info_errs = [           # |--------|--------|         
+                        errno.ESHUTDOWN,    # |   32   |   32   |
+                        errno.EAFNOSUPPORT, # |   97   |   47   |
+                        errno.ECONNRESET,   # |   104  |   54   |
+                        errno.ETIMEDOUT,    # |   110  |   60   |
+                    ]
+
+                    # fmt: on
+                    log_string = f"{gos_name} failed with code {err.errno} and will attempt to retry"
+                    if err.errno in info_errs:
+                        logger.info(log_string)
+                    else:
+                        logger.warning(log_string)
+            except Exception as err:
+                error = err
                 retry_delay = extract_retry_delay(attempt)
                 error_message = ThriftBackend._extract_error_message_from_headers(
                     getattr(self._transport, "headers", {})
                 )
-                return RequestErrorInfo(
-                    error=error,
-                    error_message=error_message,
-                    retry_delay=retry_delay,
-                    http_code=getattr(self._transport, "code", None),
-                    method=method.__name__,
-                    request=request,
-                )
+            return RequestErrorInfo(
+                error=error,
+                error_message=error_message,
+                retry_delay=retry_delay,
+                http_code=getattr(self._transport, "code", None),
+                method=method.__name__,
+                request=request,
+            )
 
         # The real work:
         # - for each available attempt:

tests/unit/test_thrift_backend.py

@@ -19,6 +19,7 @@ def retry_policy_factory():
         "_retry_delay_max":                     (float, 60, None, None),
         "_retry_stop_after_attempts_count":     (int, 30, None, None),
         "_retry_stop_after_attempts_duration":  (float, 900, None, None),
+        "_retry_delay_default":                 (float, 5, 1, 60)
     }
 
 
@@ -968,6 +969,62 @@ def test_handle_execute_response_sets_active_op_handle(self):
 
         self.assertEqual(mock_resp.operationHandle, mock_cursor.active_op_handle)
 
+    @patch("thrift.transport.THttpClient.THttpClient")
+    @patch("databricks.sql.thrift_api.TCLIService.TCLIService.Client.GetOperationStatus")
+    @patch("databricks.sql.thrift_backend._retry_policy", new_callable=retry_policy_factory)
+    def test_make_request_will_retry_GetOperationStatus(
+            self, mock_retry_policy, mock_GetOperationStatus, t_transport_class):
+       
+        import thrift, errno
+        from databricks.sql.thrift_api.TCLIService.TCLIService import Client
+        from databricks.sql.exc import RequestError
+        from databricks.sql.utils import NoRetryReason
+
+        this_gos_name = "GetOperationStatus"
+        mock_GetOperationStatus.__name__ = this_gos_name
+        mock_GetOperationStatus.side_effect = OSError(errno.ETIMEDOUT, "Connection timed out")
+
+        protocol = thrift.protocol.TBinaryProtocol.TBinaryProtocol(t_transport_class)
+        client = Client(protocol)
+
+        req = ttypes.TGetOperationStatusReq(
+            operationHandle=self.operation_handle,
+            getProgressUpdate=False,
+        )
+        
+        EXPECTED_RETRIES = 2
+
+        thrift_backend = ThriftBackend(
+            "foobar",
+            443,
+            "path", [],
+            _retry_stop_after_attempts_count=EXPECTED_RETRIES,
+            _retry_delay_default=1)
+
+
+        with self.assertRaises(RequestError) as cm:
+            thrift_backend.make_request(client.GetOperationStatus, req)
+
+        self.assertEqual(NoRetryReason.OUT_OF_ATTEMPTS.value, cm.exception.context["no-retry-reason"])
+        self.assertEqual(f'{EXPECTED_RETRIES}/{EXPECTED_RETRIES}', cm.exception.context["attempt"])
+
+        # Unusual OSError code
+        mock_GetOperationStatus.side_effect = OSError(errno.EEXIST, "File does not exist")  
+
+        with self.assertLogs("databricks.sql.thrift_backend", level=logging.WARNING) as cm:
+            with self.assertRaises(RequestError):
+                thrift_backend.make_request(client.GetOperationStatus, req)
+
+        # There should be two warning log messages: one for each retry
+        self.assertEqual(len(cm.output), EXPECTED_RETRIES)
+        
+        # The warnings should be identical
+        self.assertEqual(cm.output[1], cm.output[0])
+        
+        # The warnings should include this text
+        self.assertIn(f"{this_gos_name} failed with code {errno.EEXIST} and will attempt to retry", cm.output[0])
+    
+    
     @patch("thrift.transport.THttpClient.THttpClient")
     def test_make_request_wont_retry_if_headers_not_present(self, t_transport_class):
         t_transport_instance = t_transport_class.return_value