mrhhsg opened a new pull request, #68113:
URL: https://github.com/apache/doris/pull/68113
### What problem does this PR solve?
Issue Number: None
Problem Summary:
Sliding `ROWS` window frames evaluate `sum`/`avg` incrementally: the outgoing
row is subtracted from the accumulator and the incoming row is added. For
floating-point accumulators this is not exact. Once `2^54 + 1` rounds to
`2^54`, subtracting `2^54` again leaves `0` instead of `1`, so the rounding
lost by a value that already left the frame keeps distorting later results.
```sql
WITH t AS (
SELECT 1 AS id, CAST(18014398509481984 AS DOUBLE) AS v
UNION ALL SELECT 2, CAST(1 AS DOUBLE)
UNION ALL SELECT 3, CAST(1 AS DOUBLE)
)
SELECT id, v,
avg(v) OVER (ORDER BY id ROWS BETWEEN 1 PRECEDING AND CURRENT ROW) AS
got
FROM t ORDER BY id;
```
Before: the third row returned `0.5` (frame `[1, 1]`, sum `1`, count `2`).
After: the third row returns `1`.
Fix: `AggregateFunctionSum` and `AggregateFunctionAvg` now report
`supported_incremental_mode() == false` when the accumulator is a
floating-point type, so the analytic sink recomputes each sliding frame from
its rows (the same approach PostgreSQL takes by not providing inverse
transition functions for `float4`/`float8`). Integer and decimal accumulators
are exact and keep the incremental path. Frames that only grow
(`UNBOUNDED PRECEDING`) never removed rows and are unaffected.
Cost: sliding `ROWS` frames over `FLOAT`/`DOUBLE` columns now cost
O(frame size) per row instead of O(1). This is the trade-off for exact
results; wide sliding frames over floating-point columns will be slower.
### Release note
None
### Check List (For Author)
- Test:
- Unit Test:
`AnalyticSinkOperatorTest.SlidingRowsDouble{Avg,Sum}IgnoresRoundingOfOutgoingRow`,
`AggregateFunction{Avg,Sum}Test.test_incremental_mode_only_for_exact_sum`
- Regression test:
`query_p0/sql_functions/window_functions/test_window_float_sliding_frame`
- Behavior changed: Yes (sliding window sum/avg over FLOAT/DOUBLE now return
the exact per-frame result; wide frames are slower)
- Does this need documentation: No
https://claude.ai/code/session_01KSyhoeWWGWukpHP6MBTbEt
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