[IMPALA-11780] Wrong FILE__POSITION values for multi row group Parquet files when page filtering is used

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Impala 4.2.0
• Fix Version/s: Impala 4.3.0
• Component/s: Backend
• Labels: impala-iceberg
• Epic Color: ghx-label-13
• Assignee: Zoltán Borók-Nagy
• Reporter: Zoltán Borók-Nagy
• Created: 07/Dec/22 12:56
• Updated: 09/Dec/22 18:10
• Resolved: 09/Dec/22 18:09

Description

Impala generates wrong values for the FILE__POSITION column when the Parquet file contains multiple row groups and page filtering is being used.

We are using the value of 'current_row_' to populate the file position slot:
https://github.com/apache/impala/blob/8dbc8b733d3712035f8615f477f74c66ec9d63ea/be/src/exec/parquet/parquet-column-readers.cc#L906

Problem is that 'current_row_' denotes the index of the row within the row group and not withing the file. We cannot change 'current_row_' as page filtering depends on its value, and the page index also uses the row group-based indexes of the rows, not the file indexes.

The value of FILE__POSITION is critical for Iceberg V2 tables as position delete files store file positions of the deleted rows.