Impala Public Jenkins has submitted this change and it was merged. ( 
http://gerrit.cloudera.org:8080/24885 )

Change subject: IMPALA-15373: Fix FILE__POSITION for complex readers in later 
row groups
......................................................................

IMPALA-15373: Fix FILE__POSITION for complex readers in later row groups

ReadFilePositionNonBatched() returns 'row_group_first_row_ +
LastProcessedRow() + 1', but 'row_group_first_row_' was only assigned in
BaseScalarColumnReader::Reset(). The file position slot is attached to
(*column_readers)[0] whatever kind of reader that is, so when that is a
complex reader (collection, struct or VARIANT) the offset stayed 0 and
the second and later row groups reported row-group-relative positions.
This also mis-applies Iceberg position deletes, which match on
FILE__POSITION.

A regression from IMPALA-11780, which made 'current_row_'
row-group-relative and added the compensating term only on the scalar
path.

Pass the offset to ComplexColumnReader::Reset() as well, mirroring
InitScalarColumns(). complex_readers_ holds every complex reader,
including nested ones and the one CreateCountingReader() builds, so all
of them are covered. LastProcessedRow() stays row-group-relative, so
skip_row_id and the page index arithmetic are unaffected. ORC does not
share the bug.

Testing:
 - Two expected results in virtual-column-file-position-parquet.test
   encoded the old behaviour and are corrected to the true row indexes.
 - Added regression queries over all row groups of two different files.
 - The struct and VARIANT paths are fixed by the same change but have no
   regression test, because no checked-in file has both a top level
   struct or VARIANT column and more than one row group.
 - Ran test_scanners.py -k test_virtual_column_file_position_parquet.

Change-Id: Ieb186c5727ae2a0cd53fb0c68ac540b8cd9fa8c7
Assisted-by: Claude Fable 5.1 (Claude Code)
Reviewed-on: http://gerrit.cloudera.org:8080/24885
Reviewed-by: Zoltan Borok-Nagy <[email protected]>
Tested-by: Impala Public Jenkins <[email protected]>
---
M be/src/exec/parquet/hdfs-parquet-scanner.cc
M be/src/exec/parquet/hdfs-parquet-scanner.h
M be/src/exec/parquet/parquet-complex-column-reader.h
M 
testdata/workloads/functional-query/queries/QueryTest/virtual-column-file-position-parquet.test
4 files changed, 34 insertions(+), 10 deletions(-)

Approvals:
  Zoltan Borok-Nagy: Looks good to me, approved
  Impala Public Jenkins: Verified

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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: merged
Gerrit-Change-Id: Ieb186c5727ae2a0cd53fb0c68ac540b8cd9fa8c7
Gerrit-Change-Number: 24885
Gerrit-PatchSet: 3
Gerrit-Owner: Zoltan Borok-Nagy <[email protected]>
Gerrit-Reviewer: Csaba Ringhofer <[email protected]>
Gerrit-Reviewer: Impala Public Jenkins <[email protected]>
Gerrit-Reviewer: Xuebin Su <[email protected]>
Gerrit-Reviewer: Zoltan Borok-Nagy <[email protected]>

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