databendlabs / openraft / 29141298191

87%

Build Type

push

github

Committed by drmingdrmer

Commit Message

fix: send snapshot to a follower behind a fully-purged log

# Summary

When the leader had purged its entire log (`purge_upto == last_log_id`)
and a follower's progress was freshly reset (`matching = None`),
`next_send` returned `Err(Inflight::None)` on every call -- never
probing, never reaching the snapshot branch -- so the follower could
never converge until a new entry was proposed. It now sends a snapshot
in that dead-end.

# Details

- Reorganize the decision logic into two explicit regimes, probing and
  pipeline, plus two named snapshot conditions, so each branch states its
  own precondition instead of leaving it implied by clamp arithmetic.
- The fix lives in the probing regime: when the clamped send range
  collapses to empty (`start == end`), the leader is fully purged and the
  probe can carry no entry, so send a snapshot instead of reporting
  "nothing to replicate". The pipeline path (`LogsSince`) is untouched, so
  a follower legitimately matched at the purge boundary still streams its
  tail rather than taking a needless snapshot.
- Add `test_next_send_fully_purged_unknown_follower` covering the
  fully-purged, unknown-matching dead-end.

- Fix: #1828

Coverage Stats

20 of 20 new or added lines in 1 file covered. (100.0%)

1 existing line in 1 file now uncovered.

17471 of 20062 relevant lines covered (87.09%)

158073.92 hits per line