Window aggregate¶

Status: Native, both event-time and processing-time, with the gaps enumerated below.

This page covers the windowed GROUP BY aggregate — TUMBLE/HOP/CUMULATE/SESSION, single-phase and the two-phase local/global split — and the windowing-TVF operator that assigns each row to its window(s) ahead of a downstream consumer (an aggregate, a window join, or window Top-N/dedup).

Event-time assignment¶

TUMBLE, HOP, and CUMULATE are native only at zero offset; SESSION needs no offset. The window bounds render differently depending on the rowtime attribute's type: in the session time zone for a local-time-zone attribute, in UTC (the raw wall-clock value) for a plain TIMESTAMP.

Processing-time (proctime) assignment¶

TUMBLE/HOP/CUMULATE are native on proctime: each row is assigned to the window(s) covering the operator's current processing-time clock and fired on a processing-time timer. HOP and CUMULATE leave several windows open at once, so the timer chains — each firing emits the earliest-ending open window and schedules the next slide boundary, until the clock has passed the latest open window's end. This requires slide divides size, so every window end lands on a slide boundary.

SESSION is native on proctime too: the gap is measured on the processing-time clock, and each batch registers a cleanup timer at now + gap — the earliest the session could close with no further input. A later element extends the session (merged in the native aggregator) and registers its own later timer, so a firing emits only the sessions the clock has truly left behind by a full gap.

Proctime support is currently single-phase only: a single-phase TUMBLE/HOP/CUMULATE whose slide divides its size, or a single-phase SESSION. The two-phase local/global split is not yet on the processing-time-timer path.

Because proctime results depend on wall-clock timing, they are non-deterministic — routing and execution are tested, but the result is not byte-compared against Flink.

Windowing TVF (window assignment)¶

The windowing TVF assigns rows to windows the same way as the aggregate above — by rowtime for event-time, by the processing-time clock instead of a rowtime column for proctime — and is native under the same zero-offset TUMBLE/HOP/CUMULATE restriction; both its event-time and proctime assignment paths are native.

A downstream window join or window Top-N/dedup consuming the TVF's output closes windows on a chained processing-time timer (the same next-slide-boundary model described above) rather than a watermark, under the same slide-divides-size constraint — see those operators' own pages for their admission conditions.

Matcher declines¶

Window not event-time TUMBLE/HOP/CUMULATE (zero offset) over a local-time-zone or plain TIMESTAMP rowtime.
Proctime: anything other than a single-phase TUMBLE/HOP/CUMULATE with slide dividing size, or a single-phase SESSION — the two-phase local/global path isn't yet native on proctime.
HOP slide / CUMULATE step that doesn't divide the window size.
Key type outside bigint/int/string/boolean/date/timestamp/decimal.
A value type/aggregate mismatch.
AVG under the two-phase split — its (sum, count) buffer spans two positional partial columns. A single-phase AVG as a lone aggregate is native.
A windowed DISTINCT aggregate (SUM(DISTINCT …) etc. inside a window) — it dedups per window, which the native window operators' every-row fold would over-count. Non-windowed DISTINCT is native; see GROUP BY.

A zero-aggregate grouping-only window (GROUP BY key + window, no aggregate function) is not one of the gaps above — it's a windowed distinct, and is native (single- and two-phase), emitting one row per (key, window). See GROUP BY for how the non-windowed case handles DISTINCT.

Idle-state TTL¶

Flink applies no idle-state TTL to window operators — table.exec.state.ttl changes nothing here; windows are bounded by their own firing and eviction instead. Contrast with OVER, which does run TTL natively across all three of its frame shapes. See Configuration for the TTL flag surface.