[GitHub] [kafka] mumrah commented on a change in pull request #10097: MINOR: Add FetchSnapshot API doc in KafkaRaftClient

[GitBox <gi...@apache.org>]

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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