mumrah commented on a change in pull request #10097:
URL: https://github.com/apache/kafka/pull/10097#discussion_r574630121
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File path: raft/src/main/java/org/apache/kafka/raft/KafkaRaftClient.java
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@@ -126,9 +126,16 @@
* gracefully resign from the current epoch. This causes remaining voters
to immediately
* begin a new election.
*
- * 4) {@link FetchRequestData}: This is the same as the usual Fetch API in
Kafka, but we piggyback
- * some additional metadata on responses (i.e. current leader and epoch).
Unlike partition replication,
- * we also piggyback truncation detection on this API rather than through a
separate truncation state.
+ * 4) {@link FetchRequestData}: This is the same as the usual Fetch API in
Kafka, but we add snapshot
+ * check before responding, and we also piggyback some additional metadata
on responses (i.e. current
+ * leader and epoch). Unlike partition replication, we also piggyback
truncation detection on this API
+ * rather than through a separate truncation state.
+ *
+ * 5) {@link FetchSnapshotRequestData}: Sent by the follower to the epoch
leader to fetch snapshot when
+ * FetchResponse include a snapshot id, this happens when the follower's
log end offset is less than
+ * the leader's log start offset. This is similar to the Fetch API since
the snapshot is also stored
+ * as FileRecords, but we use {@link UnalignedRecords} in
FetchSnapshotResponse because the records is
+ * not necessarily offset-aligned.
Review comment:
```suggestion
* 5) {@link FetchSnapshotRequestData}: Sent by the follower to the epoch
leader in order to fetch a snapshot.
* This happens when a FetchResponse includes a snapshot ID due to the
follower's log end offset being less
* than the leader's log start offset. This API is similar to the Fetch
API since the snapshot is stored
* as FileRecords, but we use {@link UnalignedRecords} in
FetchSnapshotResponse because the records
* are not necessarily offset-aligned.
```
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