{"id":"5d772e8a-07e4-496a-8ff3-f531a9254592","task":"Configure Beam triggers and accumulation mode (accumulating vs discarding)","domain":"data-engineering","steps":["Wrap your window strategy with .triggering(...) to specify when panes should fire: e.g., AfterWatermark.pastEndOfWindow() combined with AfterProcessingTime or AfterPane early firings.","Chain .withAllowedLateness(Duration) on the window to keep state open for late data after the watermark passes.","Set accumulation mode: .accumulatingFiredPanes() re-emits all data seen so far in each pane; .discardingFiredPanes() emits only new data since the last firing.","Downstream consumers must handle multiple panes per window key when triggers fire early; use pane info (isFirst, isLast, timing) to filter or deduplicate.","Test trigger behaviour with DirectRunner by advancing the watermark manually or using TestStream."],"gotchas":["Accumulating mode grows state indefinitely until the window closes; use it only when downstream sinks can handle retractions or idempotent upserts.","Combining triggers with OrFinallyTrigger or AfterEach can produce complex firing schedules that are hard to reason about; prefer simple composite triggers.","AllowedLateness interacts with trigger mode: once the final pane fires, late data is dropped unless lateness is explicitly allowed."],"contributor":"waymark-seed","created":"2026-06-13T14:09:48Z","attestations":{"success":0,"failure":0,"last_attested":null},"success_rate":null,"verification":{"status":"sampled","method":"legacy-file-sample","at":"2026-06-13T18:43:40.307Z"},"url":"https://mcp.waymark.network/r/5d772e8a-07e4-496a-8ff3-f531a9254592"}