[GitHub] [arrow] sunchao commented on a change in pull request #6935: ARROW-8455: [Rust] Parquet Arrow column read on partially compatible files

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

sunchao commented on a change in pull request #6935:
URL: https://github.com/apache/arrow/pull/6935#discussion_r414235616



##########
File path: rust/parquet/src/column/reader.rs
##########
@@ -190,15 +190,12 @@ impl<T: DataType> ColumnReaderImpl<T> {
                     (self.num_buffered_values - self.num_decoded_values) as usize,
                 );
 
-                // Adjust batch size by taking into account how much space is left in
-                // values slice or levels slices (if available)
-                adjusted_size = min(adjusted_size, values.len() - values_read);
-                if let Some(ref levels) = def_levels {
-                    adjusted_size = min(adjusted_size, levels.len() - levels_read);
-                }
-                if let Some(ref levels) = rep_levels {
-                    adjusted_size = min(adjusted_size, levels.len() - levels_read);
-                }
+                // Adjust batch size by taking into account how much data there
+                // to read. As batch_size is also smaller than value and level
+                // slices (if available), this ensures that available space is not
+                // exceeded.
+                adjusted_size = min(adjusted_size, batch_size - values_read);

Review comment:
       I don't fully get this. In which case this code will yield different result than previous one. Could you give an example?




----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

For queries about this service, please contact Infrastructure at:
users@infra.apache.org