ivandika3 commented on code in PR #1334:
URL: https://github.com/apache/ratis/pull/1334#discussion_r2780609919
##########
ratis-docs/src/site/markdown/configurations.md:
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@@ -227,6 +227,29 @@ if it fails to receive any RPC responses from this peer
within this specified ti
| **Default** | false
|
+| **Property** |
`raft.server.read.read-index.leadership-heartbeat-check.skip.enabled` |
+|:----------------|:----------------------------------------------------------------------|
+| **Description** | whether to skip the leadership check heartbeat for read
index. |
+| **Type** | boolean
|
+| **Default** | false
|
+
+Note that although enabling `leadership-heartbeat-check.skip.enabled` reduce
the RTT due to the leadership check heartbeat,
+it causes reads to not be linearizable in some cases.
+This is because without the leadership check heartbeats, the leader might not
be the latest leader
+and might serve stale reads.
+There might be a small period of time when there is a split brain and two Raft
peers that believe that
+they are leaders (old leader and new leader where old leader's term < new
leader's term).
+The old leader might not have detected that it has lost majority heartbeats
and stepped down or the old leader
+has not received any RPC with higher term which forces the old leader to steps
down.
+Without the leadership check heartbeat which should detect that the old leader
is no longer the latest leader and
+force the old leader to step down, the old leader ReadIndex might return an
index that is lower than
+the new leader's applied index.
+This means that the old leader might return stale data which is not
linearizable by definition.
+However, this situation should happen only abnormal situations when the Raft
group encounters a leader election
+due to network partition between the old leader and the other majority quorum
(which will elect a new leader).
+Therefore, this might be an acceptable tradeoff for applications that seek to
improve the linearizable read
+performance.
Review Comment:
Thanks, updated.
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