[v25.3.x] raft: refresh election timer on recovery-path append_entries (pre-vote livelock) - #31255
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bharathv merged 1 commit intoAug 11, 2026
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A follower that is behind a live leader can get stuck in a perpetual pre-vote storm. `should_skip_vote` suppresses elections only while `_hbeat` (last leader contact) is within one election timeout, but in `do_append_entries` the `_hbeat` refresh lives on the successful batch-append path (a deferred update). The two early returns that fire when the follower is behind, log gap (prev_log_index > last_log_offset) and prev-log-term mismatch, call maybe_update_leader() and reply to the leader but never refresh `_hbeat`. So a follower in continuous contact with the current-term leader, but unable to append because it is still being recovered, lets its election timer expire, starts a (pre-)vote that deterministically fails the longest-log check (log_ok=false), rearms, and repeats. The storm burns CPU that further starves recovery, a self-reinforcing livelock that leaves partitions under-replicated and stalls acks=all produce with REQUEST_TIMED_OUT. Refresh `_hbeat` as soon as an append_entries from the current-term leader is accepted (right after maybe_update_leader), covering the recovery early-return paths as well as the success path. This matches the existing design intent noted in vote_request handling, where the comment states `_hbeat` is updated by the leader. Liveness is preserved: if the leader is actually gone, no append_entries arrive, `_hbeat` goes stale, and elections proceed as before. Fixes redpanda-data#30815 Signed-off-by: Steven Pall <mail@stevenpall.ca> (cherry picked from commit 81f445b)
bharathv
approved these changes
Aug 11, 2026
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Backport of PR #30817
Conflict details
Fixes: #31254,