Window TVF TUMBLE returns count=0, legacy syntax works

[Kanchi Masalia via user]

Hi Flink community,


I'm running into an issue where the legacy Group Window syntax returns
correct results but the equivalent TVF-based TUMBLE syntax returns counts
of 0 on the same source table. No errors are thrown.

*Table Definition*

CREATE TABLE event_source (
  user_id BIGINT,
  event_uuid STRING,
  raw_timestamp_ns BIGINT,
  event_time AS TO_TIMESTAMP_LTZ(raw_timestamp_ns / 1000000, 3),
  WATERMARK FOR event_time AS event_time - INTERVAL '30' SECOND
) WITH (
  'connector' = '...',
  'format' = 'json'
);



*Legacy Syntax*This works. It returns correct counts.


SELECT
  user_id,
  TUMBLE_START(event_time, INTERVAL '1' MINUTE) AS window_start,
  TUMBLE_END(event_time, INTERVAL '1' MINUTE) AS window_end,
  COUNT(*) AS cnt
FROM event_source
GROUP BY
  user_id,
  TUMBLE(event_time, INTERVAL '1' MINUTE);


*TVF Tumbling Window *

This works. It returns correct counts as 0.


SELECT
  user_id,
  window_start,
  window_end,
  COUNT(*) AS cnt
FROM TABLE(
  TUMBLE(
    TABLE event_source,
    DESCRIPTOR(event_time),
    INTERVAL '1' MINUTE
  )
)
GROUP BY
  user_id,
  window_start,
  window_end;


Observations:

   - No errors or exceptions are thrown.
   - The TVF query produces output rows, but with cnt = 0.
   - The legacy syntax produces correct non-zero counts on the same data.
   - The event_time column is a computed column of type TIMESTAMP_LTZ(3)
   derived from a nanosecond epoch.
   - When I inspect the execution plans, the legacy query uses
   *GroupWindowAggregate* as a single-phase operator and works correctly.
   The TVF query uses the two-phase *LocalWindowAggregate +
   GlobalWindowAggregate* path, and this is where the counts come back as
   0. The aggregation logic in the two-phase path appears to not be counting
   records correctly, despite receiving the same input data.

Environment:
Flink version: 1.18.1
Deployment:  Yarn

Since both queries operate on the same table with the same watermark, I
would expect identical results. The fact that the TVF path returns cnt = 0
suggests records may not be getting assigned to windows correctly in the
LocalWindowAggregate phase - possibly related to TIMESTAMP_LTZ handling in
the two-phase (local-global) execution path.

Has anyone encountered similar behavior? Any pointers would be appreciated.


Thanks,
Kanchi Masalia