Apoorv Mittal d193373f24 KAFKA-21344: Handle partition rotation for share fetches (#23951) ...

A share fetch hands its record budget to partitions in the order they
are read, so the partition read first  takes the largest share. Two
things decided that order earlier and together they could starve a
partition, hence changed the behaviour.

Earlier:
- `SharePartitionManager` rotated the fetch list by `sessionEpoch %
size`. The client bumps the epoch on both
  ShareFetch and ShareAcknowledge, so in a poll-and-commit loop fetch
epochs step by two and the rotation is
  constant. One unpaired request flips the parity, and with two
partitions the rotation then undoes the
  session reorder on every fetch, so the same partition is read first
until the other starves.
- `ShareSessionContext` moved served partitions to the end of the
session from inside the response iterator,
  in the iteration order of the response map. That map had passed
through `HashMap` copies, so when every
  partition returned records the session ended up in hash order and the
same partition led every fetch.

PR:

This change removes the epoch rotation from the fetch path and makes the
session reorder deterministic from  the fetch order. The fetch order is
preserved through `ShareFetchUtils`, `ShareFetch` and `KafkaApis` with
`LinkedHashMap`s. `ShareSessionContext` reorders the session in one pass
before pruning the response:  partitions without records keep their
position at the front, and partitions with records are appended in fetch
order rotated by one, so the partition read first is read last next
time. `PartitionRotateStrategy`  is reduced to that rotation and the
unused `sessionEpoch` parameter of `fetchMessages` is dropped.

`ShareConsumerFairnessTest` adds cases for the epoch parity change, for
the first position rotating when all partitions return records with
explicit and implicit acknowledgement, and for an idle partition being
read first once it has records.

`SharePartitionManagerTest` verifies the session order across subsequent
fetches.

Reviewers: Abhinav Dixit <adixit@confluent.io>, Andrew Schofield
 <aschofield@confluent.io>

2026-10-26 11:38:34 +00:00

..

src

KAFKA-21344: Handle partition rotation for share fetches (#23951)

2026-10-26 11:38:34 +00:00