raishakti-1983 opened a new issue, #37664:
URL: https://github.com/apache/beam/issues/37664
### What happened?
**Environment:**
Beam SDK: 2.66.0 (stable) vs 2.71.0 (problematic)
Runner: Google Cloud Dataflow (Streaming)
Language: Java
Source: KafkaIO
**Pipeline Structure**
KafkaIO
→ MapElements (KafkaRecordToKV)
→ Window.into(...)
→ GroupByKey
→ Sort
→ BigtableIO read/ write
→ Write to Kafka
**Window / Trigger configuration**
window
.triggering(
AfterWatermark.pastEndOfWindow()
.withEarlyFirings(
AfterPane.elementCountAtLeast(elementCount))
.withLateFirings(
AfterPane.elementCountAtLeast(lateElementCount)))
.discardingFiredPanes()
.withAllowedLateness(Duration.standardSeconds(allowedLateness));
window duration: 1 sec
allowed lateness: 600 sec
early count: 100
late count: 1
**Observed behavior**
**Beam 2.66**
Stable message delay, not a big accumulation at GroupAndSort step.
Data Freshness graph shows a stable pattern
**Beam 2.71**
Delay shows saw-tooth pattern (buffer → flush cycles). Seems
accumulate significantly larger panes before flushing
**Important observation**
No code or traffic change — only Beam version upgrade.
<img width="1795" height="532" alt="Image"
src="https://github.com/user-attachments/assets/1457d3ba-5bc4-4407-a702-642ba9f8298c";
/>
<img width="1839" height="671" alt="Image"
src="https://github.com/user-attachments/assets/488b2e7c-af00-422a-aaf3-e2fc98776e25";
/>
### Issue Priority
Priority: 2 (default / most bugs should be filed as P2)
### Issue Components
- [ ] Component: Python SDK
- [x] Component: Java SDK
- [ ] Component: Go SDK
- [ ] Component: Typescript SDK
- [ ] Component: IO connector
- [ ] Component: Beam YAML
- [ ] Component: Beam examples
- [ ] Component: Beam playground
- [ ] Component: Beam katas
- [ ] Component: Website
- [ ] Component: Infrastructure
- [ ] Component: Spark Runner
- [ ] Component: Flink Runner
- [ ] Component: Samza Runner
- [ ] Component: Twister2 Runner
- [ ] Component: Hazelcast Jet Runner
- [ ] Component: Google Cloud Dataflow Runner
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