[GitHub] [arrow] alamb commented on a change in pull request #8007: ARROW-9790: [Rust][Parquet] Fix PrimitiveArrayReader boundary conditions

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alamb commented on a change in pull request #8007:
URL: https://github.com/apache/arrow/pull/8007#discussion_r473045357



##########
File path: rust/parquet/src/arrow/array_reader.rs
##########
@@ -136,10 +136,8 @@ impl<T: DataType> ArrayReader for PrimitiveArrayReader<T> {
         while records_read < batch_size {
             let records_to_read = batch_size - records_read;
 
+            // NB can be 0 if at end of page
             let records_read_once = self.record_reader.read_records(records_to_read)?;
-            if records_read_once == 0 {

Review comment:
       The case of `0` rows being read is handled in the `if records_read_once < records_to-read` clause below -- namely in this case the code needs to try and get the next page of data from the page reader. 

##########
File path: rust/parquet/src/arrow/arrow_reader.rs
##########
@@ -304,6 +304,45 @@ mod tests {
         >(2, 100, 2, message_type, 15, 50, converter);
     }
 
+    #[test]

Review comment:
       Both these tests fail without the changes in this PR.
   
   I don't like the copy/paste nature of these tests and I plan a minor PR building on this one proposing how to remove the duplication and make the tests easier to read. 




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