[GitHub] [beam] vachan-shetty commented on a change in pull request #15185: [BEAM-10917] Add support for BigQuery Read API in Python BEAM

[GitBox <gi...@apache.org>]

vachan-shetty commented on a change in pull request #15185:
URL: https://github.com/apache/beam/pull/15185#discussion_r681124938



##########
File path: sdks/python/apache_beam/io/gcp/bigquery.py
##########
@@ -883,6 +895,221 @@ def _export_files(self, bq):
     return table.schema, metadata_list
 
 
+class _CustomBigQueryStorageSourceBase(BoundedSource):
+  """A base class for BoundedSource implementations which read from BigQuery
+  using the BigQuery Storage API.
+
+  Args:
+    table (str, TableReference): The ID of the table. The ID must contain only
+      letters ``a-z``, ``A-Z``, numbers ``0-9``, or underscores ``_``  If
+      **dataset** argument is :data:`None` then the table argument must
+      contain the entire table reference specified as:
+      ``'PROJECT:DATASET.TABLE'`` or must specify a TableReference.
+    dataset (str): The ID of the dataset containing this table or
+      :data:`None` if the table argument specifies a TableReference.
+    project (str): The ID of the project containing this table or
+      :data:`None` if the table argument specifies a TableReference.
+    selected_fields (List[str]): Names of the fields in the table that should be
+      read. If empty, all fields will be read. If the specified field is a
+      nested field, all the sub-fields in the field will be selected. The output
+      field order is unrelated to the order of fields in selected_fields.
+    row_restriction (str): SQL text filtering statement, similar to a WHERE
+      clause in a query. Aggregates are not supported.Restricted to a maximum
+      length for 1 MB.
+  """
+
+  # The maximum number of streams which will be requested when creating a read
+  # session, regardless of the desired bundle size.
+  MAX_SPLIT_COUNT = 10000
+  # The minimum number of streams which will be requested when creating a read
+  # session, regardless of the desired bundle size. Note that the server may
+  # still choose to return fewer than ten streams based on the layout of the
+  # table.
+  MIN_SPLIT_COUNT = 10
+
+  def __init__(
+      self,
+      table: Union[str, TableReference],
+      dataset: str = None,
+      project: str = None,
+      selected_fields: List[str] = None,
+      row_restriction: str = None,
+      pipeline_options: GoogleCloudOptions = None):
+
+    self.table_reference = bigquery_tools.parse_table_reference(
+        table, dataset, project)
+    self.project = self.table_reference.projectId
+    self.dataset = self.table_reference.datasetId
+    self.table = self.table_reference.tableId
+    self.selected_fields = selected_fields
+    self.row_restriction = row_restriction
+    self.pipeline_options = pipeline_options
+    self.split_result = None
+
+  def _get_parent_project(self):
+    """Returns the project that will be billed."""
+    project = self.pipeline_options.view_as(GoogleCloudOptions).project
+    if isinstance(project, vp.ValueProvider):
+      project = project.get()
+    if not project:
+      project = self.project
+    return project
+
+  def _get_table_size(self, table, dataset, project):
+    if project is None:
+      project = self._get_parent_project()
+
+    bq = bigquery_tools.BigQueryWrapper()
+    table = bq.get_table(project, dataset, table)
+    return table.numBytes
+
+  def display_data(self):
+    return {
+        'project': str(self.project),
+        'dataset': str(self.dataset),
+        'table': str(self.table),
+        'selected_fields': str(self.selected_fields),
+        'row_restriction': str(self.row_restriction)
+    }
+
+  def estimate_size(self):
+    # The size of stream source cannot be estimate due to server-side liquid
+    # sharding
+    return None
+
+  def split(self, desired_bundle_size, start_position=None, stop_position=None):
+    requested_session = bq_storage.types.ReadSession()
+    requested_session.table = 'projects/{}/datasets/{}/tables/{}'.format(
+        self.project, self.dataset, self.table)
+    requested_session.data_format = bq_storage.types.DataFormat.AVRO
+    if self.selected_fields is not None:
+      requested_session.read_options.selected_fields = self.selected_fields
+    if self.row_restriction is not None:
+      requested_session.read_options.row_restriction = self.row_restriction
+
+    storage_client = bq_storage.BigQueryReadClient()
+    stream_count = 0
+    if (desired_bundle_size > 0):
+      table_size = self._get_table_size(self.table, self.dataset, self.project)
+      stream_count = min(
+          int(table_size / desired_bundle_size),
+          _CustomBigQueryStorageSourceBase.MAX_SPLIT_COUNT)
+    stream_count = max(
+        stream_count, _CustomBigQueryStorageSourceBase.MIN_SPLIT_COUNT)
+
+    parent = 'projects/{}'.format(self.project)
+    read_session = storage_client.create_read_session(
+        parent=parent,
+        read_session=requested_session,
+        max_stream_count=stream_count)
+
+    self.split_result = [
+        _CustomBigQueryStorageStreamSource(stream.name)
+        for stream in read_session.streams
+    ]
+
+    for source in self.split_result:
+      yield SourceBundle(
+          weight=1.0, source=source, start_position=None, stop_position=None)
+
+  def get_range_tracker(self, start_position, stop_position):
+    class NonePositionRangeTracker(RangeTracker):
+      """A RangeTracker that always returns positions as None. Prevents the
+      BigQuery Storage source from being read() before being split()."""
+      def start_position(self):
+        return None
+
+      def stop_position(self):
+        return None
+
+    return NonePositionRangeTracker()
+
+  def read(self, range_tracker):
+    raise NotImplementedError(
+        'BigQuery storage source must be split before being read')
+
+
+class _CustomBigQueryStorageStreamSource(BoundedSource):
+  """A source representing a single stream in a read session."""
+  def __init__(self, read_stream_name: str):
+    self.read_stream_name = read_stream_name
+
+  def display_data(self):
+    return {
+        'read_stream': str(self.read_stream_name),
+    }
+
+  def estimate_size(self):
+    # The size of stream source cannot be estimate due to server-side liquid

Review comment:
       Added a TODO. We will be implementing this at some point.




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