**Section 1 — The Context (The 'Why')**
Spark DAG, stages, tasks. collect() to driver causes OOM. AQE coalesce reduces shuffle. A naive developer enables cache everywhere.
**Section 2 — The Diagram**
```
[Driver]
DAG | Stages | Tasks
|
+-> [Exec 1..N]
Cache | Shuffle
|
v
[Cluster Mgr]
```
**Section 3 — Component Logic**
**Driver** constructs DAG. **Executors** run tasks; cache; shuffle. AQE coalesce. collect() = driver OOM. take() or write to S3....
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