ahmedabu98 commented on code in PR #38015:
URL: https://github.com/apache/beam/pull/38015#discussion_r3018441740


##########
sdks/python/apache_beam/io/gcp/bigquery_change_history.py:
##########
@@ -1170,16 +1315,46 @@ def expand(self, pbegin: beam.pvalue.PBegin) -> 
beam.PCollection:
                 row_filter=self._row_filter))
         | 'CommitQueryResults' >> beam.Reshuffle())
 
+    emit_raw = self._decompress_shards is not None
+
+    read_sdf = beam.ParDo(
+        _ReadStorageStreamsSDF(
+            batch_arrow_read=self._batch_arrow_read,
+            change_timestamp_column=self._change_timestamp_column,
+            max_split_rounds=self._max_split_rounds,
+            emit_raw_batches=emit_raw))
+    if emit_raw:
+      read_sdf = read_sdf.with_output_types(Tuple[bytes, bytes])
+    else:
+      read_sdf = read_sdf.with_output_types(Dict[str, Any])
+
     read_outputs = (
         query_results
-        | 'ReadStorageStreams' >> beam.ParDo(
-            _ReadStorageStreamsSDF(
-                batch_arrow_read=self._batch_arrow_read,
-                change_timestamp_column=self._change_timestamp_column)).
-        with_outputs(_CLEANUP_TAG, main='rows'))
+        | 'ReadStorageStreams' >> read_sdf.with_outputs(
+            _CLEANUP_TAG, main='rows'))
 
     _ = (
         read_outputs[_CLEANUP_TAG]
         | 'CleanupTempTables' >> beam.ParDo(_CleanupTempTablesFn()))
 
-    return read_outputs['rows']
+    if emit_raw:
+      # Fan out raw Arrow batches across decompress_shards workers
+      # via GBK, then decompress and convert to timestamped row dicts.
+      # Uses a discarding trigger so GBK fires per-element without
+      # waiting for the GlobalWindow to close.
+      num_shards = self._decompress_shards
+      rows = (
+          read_outputs['rows']
+          | 'ShardBatches' >>
+          beam.WithKeys(lambda _, n=num_shards: random.randint(0, n - 1))
+          | 'WindowForGBK' >> beam.WindowInto(
+              GlobalWindows(),
+              trigger=beam_trigger.Repeatedly(beam_trigger.AfterCount(1)),
+              accumulation_mode=(beam_trigger.AccumulationMode.DISCARDING))
+          | 'GroupByShardKey' >> beam.GroupByKey()

Review Comment:
   Side note: is there a benefit of doing it in-line instead of doing the 
decompress fan-out?



##########
sdks/python/apache_beam/io/gcp/bigquery_change_history.py:
##########
@@ -1170,16 +1315,46 @@ def expand(self, pbegin: beam.pvalue.PBegin) -> 
beam.PCollection:
                 row_filter=self._row_filter))
         | 'CommitQueryResults' >> beam.Reshuffle())
 
+    emit_raw = self._decompress_shards is not None
+
+    read_sdf = beam.ParDo(
+        _ReadStorageStreamsSDF(
+            batch_arrow_read=self._batch_arrow_read,
+            change_timestamp_column=self._change_timestamp_column,
+            max_split_rounds=self._max_split_rounds,
+            emit_raw_batches=emit_raw))
+    if emit_raw:
+      read_sdf = read_sdf.with_output_types(Tuple[bytes, bytes])
+    else:
+      read_sdf = read_sdf.with_output_types(Dict[str, Any])
+
     read_outputs = (
         query_results
-        | 'ReadStorageStreams' >> beam.ParDo(
-            _ReadStorageStreamsSDF(
-                batch_arrow_read=self._batch_arrow_read,
-                change_timestamp_column=self._change_timestamp_column)).
-        with_outputs(_CLEANUP_TAG, main='rows'))
+        | 'ReadStorageStreams' >> read_sdf.with_outputs(
+            _CLEANUP_TAG, main='rows'))
 
     _ = (
         read_outputs[_CLEANUP_TAG]
         | 'CleanupTempTables' >> beam.ParDo(_CleanupTempTablesFn()))
 
-    return read_outputs['rows']
+    if emit_raw:
+      # Fan out raw Arrow batches across decompress_shards workers
+      # via GBK, then decompress and convert to timestamped row dicts.
+      # Uses a discarding trigger so GBK fires per-element without
+      # waiting for the GlobalWindow to close.
+      num_shards = self._decompress_shards
+      rows = (
+          read_outputs['rows']
+          | 'ShardBatches' >>
+          beam.WithKeys(lambda _, n=num_shards: random.randint(0, n - 1))
+          | 'WindowForGBK' >> beam.WindowInto(
+              GlobalWindows(),
+              trigger=beam_trigger.Repeatedly(beam_trigger.AfterCount(1)),
+              accumulation_mode=(beam_trigger.AccumulationMode.DISCARDING))
+          | 'GroupByShardKey' >> beam.GroupByKey()

Review Comment:
   Side question: is there a benefit of doing it in-line instead of doing the 
decompress fan-out?



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