tongwai-wong-appier commented on issue #16282:
URL: https://github.com/apache/iceberg/issues/16282#issuecomment-5082844093
Assume a zombie coordinator exists — the split-brain case your PR is about,
where a previous
leader's `close()` never reached `stopCoordinator()`, so two coordinators
are members of
`<group>-coord` and the healthy one holds the control-topic partition.
The rewind doesn't need a `seek()` — it needs a *different* member to leave
the group.
- Zombie shuts down: `CommitterImpl.close()` → `stopCoordinator()` →
`CoordinatorThread.terminate()`
→ `Channel.stop()` → `consumer.close()` → **LeaveGroup**
- Membership change → `<group>-coord` rebalances → the *surviving*
coordinator has to rejoin, even
though it's healthy and keeps the same partition
- No `partition.assignment.strategy` set → client default `[RangeAssignor,
CooperativeStickyAssignor]`
→ protocol comes from the first entry = **eager** → all partitions
revoked, fetch positions
discarded → `updateFetchPositions()` refetches the committed offset.
That's the rewind, inside the
consumer — nothing to grep for.
- Nothing is constructed on that path and no `ConsumerRebalanceListener` is
registered, so
`commitBuffer` / `currentCommitId` / `controlTopicOffsets` are untouched.
**That's t2**: buffer 0–7,
`{0:8}`, position 0.
- Replayed records carry the current `commitId` (the group offset only
advances on a successful
`doCommit()`), so `isCommitReady()` fires mid-drain at 8+2 = 10 — the
commit runs while the map is
`{0:2}`.
Your co-reset invariant covers the Coordinator being constructed, not the
one already running.
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