[Graphbolt] Use dynamic buffer size for shuffle. (#6040)

Co-authored-by: Ubuntu <ubuntu@ip-172-31-28-63.ap-northeast-1.compute.internal>

python/dgl/graphbolt/minibatch_sampler.py

@@ -186,7 +186,10 @@ class MinibatchSampler(IterDataPipe):
         # Shuffle before batch.
         if self._shuffle:
             # `torchdata.datapipes.iter.Shuffler` works with stream too.
-            data_pipe = data_pipe.shuffle()
+            # To ensure randomness, make sure the buffer size is at least 10
+            # times the batch size.
+            buffer_size = max(10000, 10 * self._batch_size)
+            data_pipe = data_pipe.shuffle(buffer_size=buffer_size)
 
         # Batch.
         data_pipe = data_pipe.batch(