if appendLog failed after rpc return, use a different error code (ves…

…oft-inc#626)

Co-authored-by: Doodle <13706157+critical27@users.noreply.github.com>

Co-authored-by: lionel.liu@vesoft.com <52276794+liuyu85cn@users.noreply.github.com>
Co-authored-by: Doodle <13706157+critical27@users.noreply.github.com>

src/interface/common.thrift

@@ -485,6 +485,7 @@ enum ErrorCode {
  E_RAFT_LOG_GAP = -3501,
  E_RAFT_LOG_STALE = -3502,
  E_RAFT_TERM_OUT_OF_DATE = -3503,
+ E_RAFT_UNKNOWN_APPEND_LOG = -3504,
  // Raft state errors
  E_RAFT_WAITING_SNAPSHOT = -3511,
  E_RAFT_SENDING_SNAPSHOT = -3512,

src/kvstore/raftex/RaftPart.cpp

@@ -880,7 +880,12 @@ void RaftPart::processAppendLogResponses(const AppendLogResponses& resps,
  leader_ = HostAddr("", 0);
  lastLogId_ = wal_->lastLogId();
  lastLogTerm_ = wal_->lastLogTerm();
- res = nebula::cpp2::ErrorCode::E_RAFT_TERM_OUT_OF_DATE;
+ // It is nature to return E_RAFT_TERM_OUT_OF_DATE or LEADER_CHANGE
+ // here, but this will make caller believe this append failed
+ // however, this log is replicated to followers(written in WAL)
+ // and those followers may become leader (use that WAL)
+ // which means this log may actully commit succeeded.
+ res = nebula::cpp2::ErrorCode::E_RAFT_UNKNOWN_APPEND_LOG;
  }
  }
  if (!checkAppendLogResult(res)) {