Fix for cloud fetch

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Release History
 
+# 3.1.1 (2024-02-21)
+
+- Fix: Cloud fetch file download errors (#356)
+
 # 3.1.0 (2024-02-16)
 
 - Revert retry-after behavior to be exponential backoff (#349)

examples/custom_logger.py

@@ -0,0 +1,33 @@
+from databricks import sql
+import os
+import logging
+
+
+logger = logging.getLogger("databricks.sql")
+logger.setLevel(logging.DEBUG)
+fh = logging.FileHandler("pysqllogs.log")
+fh.setFormatter(logging.Formatter("%(asctime)s %(levelname)s %(process)d %(thread)d %(message)s"))
+fh.setLevel(logging.DEBUG)
+logger.addHandler(fh)
+
+with sql.connect(
+ server_hostname=os.getenv("DATABRICKS_SERVER_HOSTNAME"),
+ http_path=os.getenv("DATABRICKS_HTTP_PATH"),
+ access_token=os.getenv("DATABRICKS_TOKEN"),
+ use_cloud_fetch=True,
+ max_download_threads = 2
+) as connection:
+
+ with connection.cursor(arraysize=1000, buffer_size_bytes=54857600) as cursor:
+ print(
+ "executing query: SELECT * FROM range(0, 20000000) AS t1 LEFT JOIN (SELECT 1) AS t2"
+ )
+ cursor.execute("SELECT * FROM range(0, 20000000) AS t1 LEFT JOIN (SELECT 1) AS t2")
+ try:
+ while True:
+ row = cursor.fetchone()
+ if row is None:
+ break
+ print(f"row: {row}")
+ except sql.exc.ResultSetDownloadError as e:
+ print(f"error: {e}")

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "databricks-sql-connector"
-version = "3.1.0"
+version = "3.1.1"
 description = "Databricks SQL Connector for Python"
 authors = ["Databricks <databricks-sql-connector-maintainers@databricks.com>"]
 license = "Apache-2.0"

src/databricks/sql/__init__.py

@@ -62,7 +62,7 @@ def __repr__(self):
 DATE = DBAPITypeObject("date")
 ROWID = DBAPITypeObject()
 
-__version__ = "3.1.0"
+__version__ = "3.1.1"
 USER_AGENT_NAME = "PyDatabricksSqlConnector"
 
 # These two functions are pyhive legacy

src/databricks/sql/cloudfetch/download_manager.py

@@ -8,6 +8,7 @@
  ResultSetDownloadHandler,
  DownloadableResultSettings,
 )
+from databricks.sql.exc import ResultSetDownloadError
 from databricks.sql.thrift_api.TCLIService.ttypes import TSparkArrowResultLink
 
 logger = logging.getLogger(__name__)
@@ -34,8 +35,6 @@ def __init__(self, max_download_threads: int, lz4_compressed: bool):
  self.download_handlers: List[ResultSetDownloadHandler] = []
  self.thread_pool = ThreadPoolExecutor(max_workers=max_download_threads + 1)
  self.downloadable_result_settings = DownloadableResultSettings(lz4_compressed)
- self.fetch_need_retry = False
- self.num_consecutive_result_file_download_retries = 0
 
  def add_file_links(
  self, t_spark_arrow_result_links: List[TSparkArrowResultLink]
@@ -81,13 +80,15 @@ def get_next_downloaded_file(
 
  # Find next file
  idx = self._find_next_file_index(next_row_offset)
+ # is this correct?
  if idx is None:
  self._shutdown_manager()
+ logger.debug("could not find next file index")
  return None
  handler = self.download_handlers[idx]
 
  # Check (and wait) for download status
- if self._check_if_download_successful(handler):
+ if handler.is_file_download_successful():
  # Buffer should be empty so set buffer to new ArrowQueue with result_file
  result = DownloadedFile(
  handler.result_file,
@@ -97,9 +98,11 @@ def get_next_downloaded_file(
  self.download_handlers.pop(idx)
  # Return True upon successful download to continue loop and not force a retry
  return result
- # Download was not successful for next download item, force a retry
+ # Download was not successful for next download item. Fail
  self._shutdown_manager()
- return None
+ raise ResultSetDownloadError(
+ f"Download failed for result set starting at {next_row_offset}"
+ )
 
  def _remove_past_handlers(self, next_row_offset: int):
  # Any link in which its start to end range doesn't include the next row to be fetched does not need downloading
@@ -133,33 +136,6 @@ def _find_next_file_index(self, next_row_offset: int):
  ]
  return next_indices[0] if len(next_indices) > 0 else None
 
- def _check_if_download_successful(self, handler: ResultSetDownloadHandler):
- # Check (and wait until download finishes) if download was successful
- if not handler.is_file_download_successful():
- if handler.is_link_expired:
- self.fetch_need_retry = True
- return False
- elif handler.is_download_timedout:
- # Consecutive file retries should not exceed threshold in settings
- if (
- self.num_consecutive_result_file_download_retries
- >= self.downloadable_result_settings.max_consecutive_file_download_retries
- ):
- self.fetch_need_retry = True
- return False
- self.num_consecutive_result_file_download_retries += 1
-
- # Re-submit handler run to thread pool and recursively check download status
- self.thread_pool.submit(handler.run)
- return self._check_if_download_successful(handler)
- else:
- self.fetch_need_retry = True
- return False
-
- self.num_consecutive_result_file_download_retries = 0
- self.fetch_need_retry = False
- return True
-
  def _shutdown_manager(self):
  # Clear download handlers and shutdown the thread pool
  self.download_handlers = []

src/databricks/sql/cloudfetch/downloader.py

@@ -1,15 +1,17 @@
 import logging
 from dataclasses import dataclass
-
 import requests
 import lz4.frame
 import threading
 import time
-
+import os
+import re
 from databricks.sql.thrift_api.TCLIService.ttypes import TSparkArrowResultLink
 
 logger = logging.getLogger(__name__)
 
+DEFAULT_CLOUD_FILE_TIMEOUT = int(os.getenv("DATABRICKS_CLOUD_FILE_TIMEOUT", 180))
+
 
 @dataclass
 class DownloadableResultSettings:
@@ -20,13 +22,17 @@ class DownloadableResultSettings:
  is_lz4_compressed (bool): Whether file is expected to be lz4 compressed.
  link_expiry_buffer_secs (int): Time in seconds to prevent download of a link before it expires. Default 0 secs.
  download_timeout (int): Timeout for download requests. Default 60 secs.
- max_consecutive_file_download_retries (int): Number of consecutive download retries before shutting down.
+ download_max_retries (int): Number of consecutive download retries before shutting down.
+ max_retries (int): Number of consecutive download retries before shutting down.
+ backoff_factor (int): Factor to increase wait time between retries.
+
  """
 
  is_lz4_compressed: bool
  link_expiry_buffer_secs: int = 0
- download_timeout: int = 60
- max_consecutive_file_download_retries: int = 0
+ download_timeout: int = DEFAULT_CLOUD_FILE_TIMEOUT
+ max_retries: int = 5
+ backoff_factor: int = 2
 
 
 class ResultSetDownloadHandler(threading.Thread):
@@ -57,16 +63,21 @@ def is_file_download_successful(self) -> bool:
  else None
  )
  try:
+ logger.debug(
+ f"waiting for at most {timeout} seconds for download file: startRow {self.result_link.startRowOffset}, rowCount {self.result_link.rowCount}, endRow {self.result_link.startRowOffset + self.result_link.rowCount}"
+ )
+
  if not self.is_download_finished.wait(timeout=timeout):
  self.is_download_timedout = True
- logger.debug(
- "Cloud fetch download timed out after {} seconds for link representing rows {} to {}".format(
- self.settings.download_timeout,
- self.result_link.startRowOffset,
- self.result_link.startRowOffset + self.result_link.rowCount,
- )
+ logger.error(
+ f"cloud fetch download timed out after {self.settings.download_timeout} seconds for link representing rows {self.result_link.startRowOffset} to {self.result_link.startRowOffset + self.result_link.rowCount}"
  )
- return False
+ # there are some weird cases when the is_download_finished is not set, but the file is downloaded successfully
+ return self.is_file_downloaded_successfully
+
+ logger.debug(
+ f"finish waiting for download file: startRow {self.result_link.startRowOffset}, rowCount {self.result_link.rowCount}, endRow {self.result_link.startRowOffset + self.result_link.rowCount}"
+ )
  except Exception as e:
  logger.error(e)
  return False
@@ -81,24 +92,36 @@ def run(self):
  """
  self._reset()
 
- # Check if link is already expired or is expiring
- if ResultSetDownloadHandler.check_link_expired(
- self.result_link, self.settings.link_expiry_buffer_secs
- ):
- self.is_link_expired = True
- return
+ try:
+ # Check if link is already expired or is expiring
+ if ResultSetDownloadHandler.check_link_expired(
+ self.result_link, self.settings.link_expiry_buffer_secs
+ ):
+ self.is_link_expired = True
+ return
 
- session = requests.Session()
- session.timeout = self.settings.download_timeout
+ logger.debug(
+ f"started to download file: startRow {self.result_link.startRowOffset}, rowCount {self.result_link.rowCount}, endRow {self.result_link.startRowOffset + self.result_link.rowCount}"
+ )
 
- try:
  # Get the file via HTTP request
- response = session.get(self.result_link.fileLink)
+ response = http_get_with_retry(
+ url=self.result_link.fileLink,
+ max_retries=self.settings.max_retries,
+ backoff_factor=self.settings.backoff_factor,
+ download_timeout=self.settings.download_timeout,
+ )
 
- if not response.ok:
- self.is_file_downloaded_successfully = False
+ if not response:
+ logger.error(
+ f"failed downloading file: startRow {self.result_link.startRowOffset}, rowCount {self.result_link.rowCount}, endRow {self.result_link.startRowOffset + self.result_link.rowCount}"
+ )
  return
 
+ logger.debug(
+ f"success downloading file: startRow {self.result_link.startRowOffset}, rowCount {self.result_link.rowCount}, endRow {self.result_link.startRowOffset + self.result_link.rowCount}"
+ )
+
  # Save (and decompress if needed) the downloaded file
  compressed_data = response.content
  decompressed_data = (
@@ -109,15 +132,22 @@ def run(self):
  self.result_file = decompressed_data
 
  # The size of the downloaded file should match the size specified from TSparkArrowResultLink
- self.is_file_downloaded_successfully = (
- len(self.result_file) == self.result_link.bytesNum
+ success = len(self.result_file) == self.result_link.bytesNum
+ logger.debug(
+ f"download successful file: startRow {self.result_link.startRowOffset}, rowCount {self.result_link.rowCount}, endRow {self.result_link.startRowOffset + self.result_link.rowCount}"
  )
+ self.is_file_downloaded_successfully = success
  except Exception as e:
+ logger.error(
+ f"exception downloading file: startRow {self.result_link.startRowOffset}, rowCount {self.result_link.rowCount}, endRow {self.result_link.startRowOffset + self.result_link.rowCount}"
+ )
  logger.error(e)
  self.is_file_downloaded_successfully = False
 
  finally:
- session and session.close()
+ logger.debug(
+ f"signal finished file: startRow {self.result_link.startRowOffset}, rowCount {self.result_link.rowCount}, endRow {self.result_link.startRowOffset + self.result_link.rowCount}"
+ )
  # Awaken threads waiting for this to be true which signals the run is complete
  self.is_download_finished.set()
 
@@ -145,6 +175,7 @@ def check_link_expired(
  link.expiryTime < current_time
  or link.expiryTime - current_time < expiry_buffer_secs
  ):
+ logger.debug("link expired")
  return True
  return False
 
@@ -171,3 +202,40 @@ def decompress_data(compressed_data: bytes) -> bytes:
  uncompressed_data += data
  start += num_bytes
  return uncompressed_data
+
+
+def http_get_with_retry(url, max_retries=5, backoff_factor=2, download_timeout=60):
+ attempts = 0
+ pattern = re.compile(r"(\?|&)([\w-]+)=([^&\s]+)")
+ mask = r"\1\2=<REDACTED>"
+
+ # TODO: introduce connection pooling. I am seeing weird errors without it.
+ while attempts < max_retries:
+ try:
+ session = requests.Session()
+ session.timeout = download_timeout
+ response = session.get(url)
+
+ # Check if the response status code is in the 2xx range for success
+ if response.status_code == 200:
+ return response
+ else:
+ logger.error(response)
+ except Exception as e:
+ # if this is not redacted, it will print the pre-signed URL
+ logger.error(
+ f"request failed with exception: {re.sub(pattern, mask, str(e))}"
+ )
+ finally:
+ session.close()
+ # Exponential backoff before the next attempt
+ wait_time = backoff_factor**attempts
+ logger.info(f"retrying in {wait_time} seconds...")
+ time.sleep(wait_time)
+
+ attempts += 1
+
+ logger.error(
+ f"exceeded maximum number of retries ({max_retries}) while downloading result."
+ )
+ return None

src/databricks/sql/exc.py

@@ -115,3 +115,7 @@ class SessionAlreadyClosedError(RequestError):
 
 class CursorAlreadyClosedError(RequestError):
  """Thrown if CancelOperation receives a code 404. ThriftBackend should gracefully proceed as this is expected."""
+
+
+class ResultSetDownloadError(RequestError):
+ """Thrown if there was an error during the download of a result set"""