WAL Proposer 完整状态机
全局状态：wp->state（WalProposerState）
WPS_COLLECTING_TERMS → WPS_CAMPAIGN → WPS_ELECTED 收集握手/term 投票中 已当选，开始流复制
每个 Safekeeper 状态：sk->state（SafekeeperState）
┌──────────────────────────────────────────┐ │ 任何状态出错 → ShutdownConnection │ │ ↓ SS_OFFLINE │ │ ReconnectSafekeepers (每1s) │ │ ↓ ResetConnection │ └──────────────────────────────────────────┘ SS_OFFLINE ──ResetConnection──→ SS_CONNECTING_WRITE │ │ │ conn_connect_poll() │ │ │ ┌──────────────┼──────────────┐ │ ↓ ↓ ↓ │ POLLING_WRITING POLLING_READING POLLING_OK │ SS_CONNECTING_ SS_CONNECTING_ │ │ WRITE READ │ │ │ │ │ │ └── poll() ────┘ │ │ ↓ │ SendStartWALPush() │ │ │ ↓ │ SS_WAIT_EXEC_RESULT │ │ │ conn_get_query_result() │ │ │ ↓ COPYBOTH成功 │ SendProposerGreeting() │ │ [消息: ProposerGreeting 'g'] │ ↓ │ SS_HANDSHAKE_RECV │ │ │ AsyncReadMessage() → greetResponse │ │ │ ↓ │ SS_WAIT_VOTING (idle, 等待quorum) │ │ │ TermsCollected() → WPS_CAMPAIGN │ SendVoteRequest() │ │ [消息: VoteRequest 'v'] │ ↓ │ SS_WAIT_VERDICT │ │ │ AsyncReadMessage() → voteResponse │ │ │ VotesCollected() → WPS_ELECTED │ HandleElectedProposer() │ │ │ ↓ │ SS_WAIT_ELECTED (idle) │ │ │ SendProposerElected() [消息: ProposerElected 'e'] │ │ │ ↓ │ SS_SEND_ELECTED_FLUSH │ │ │ AsyncFlush() → OK │ │ │ StartStreaming() │ │ │ ↓ │ SS_ACTIVE ←── 流复制/心跳阶段 │ │ │ ┌───────────┼───────────┐ │ ↓ ↓ ↓ │ SS_ACTIVE_ SS_ACTIVE_ SS_ACTIVE_ │ SEND READ_WAL FLUSH │ │ │ │ └──── 循环 ──────────────┘ │ └── 超时/断连后回到 SS_OFFLINE，重新开始
消息流与处理函数对照表
| 阶段 | sk→wp 消息 | wp→sk 消息 | 入口函数 | sk->state 变化 |
|---|
| 连接 | - | - | ResetConnection | OFFLINE → CONNECTING_WRITE |
| TCP握手 | - | - | HandleConnectionEvent | CONNECTING_* → (polling) |
| START_WAL_PUSH | - | SQL query | SendStartWALPush | CONNECTING_* → WAIT_EXEC_RESULT |
| 执行结果 | CopyBoth响应 | - | RecvStartWALPushResult | WAIT_EXEC_RESULT → HANDSHAKE_RECV |
| 握手 | - | 'g'Greeting | SendProposerGreeting | HANDSHAKE_RECV |
| 握手响应 | 'g'Greeting | - | RecvAcceptorGreeting | HANDSHAKE_RECV → WAIT_VOTING |
| 投票开始 | - | 'v'VoteRequest | SendVoteRequest | WAIT_VOTING → WAIT_VERDICT |
| 投票响应 | 'v'VoteResponse | - | RecvVoteResponse | WAIT_VERDICT → WAIT_ELECTED |
| 宣布当选 | - | 'e'ProposerElected | SendProposerElected | WAIT_ELECTED → SEND_ELECTED_FLUSH |
| Flush | - | - | AsyncFlush→StartStreaming | SEND_ELECTED_FLUSH →SS_ACTIVE |
| WAL/心跳 | 'a'AppendResponse | 'a'AppendRequest | HandleActiveState | SS_ACTIVE 循环 |
| 断连 | - | - | ShutdownConnection | 任意 →SS_OFFLINE |
SS_ACTIVE 子状态循环
SS_ACTIVE_SEND ──SendAppendRequests()──→ SS_ACTIVE_READ_WAL ↑ │ │ wal_read() 读WAL │ │ │ conn_async_write() │ │ │ ┌───────────┼───────────┐ │ ↓ ↓ ↓ │ WRITE_SUCCESS TRY_FLUSH WRITE_FAIL │ │ │ │ │ SS_ACTIVE_SEND SS_ACTIVE ShutdownConnection │ │ _FLUSH ↓ │ │ │ SS_OFFLINE │ │ AsyncFlush() │ │ │ │ └────┬────┘ │ │ └──── 同时可接收 AppendResponse ──┘ RecvAppendResponses() → HandleSafekeeperResponse() → GetAcknowledgedByQuorumWALPosition() → commitLsn 推进 → BroadcastAppendRequest()
Global 状态转换（wp->state）
WPS_COLLECTING_TERMS │ 每收到一个 Greeting → 检查 TermsCollected() │ 条件: n_connected >= quorum (≥2) │ → 设置 propTerm, voteRequest ↓ WPS_CAMPAIGN │ 每收到一个 VoteResponse → 检查 VotesCollected() │ 条件: quorum 个 safekeeper 在 SS_WAIT_ELECTED │ → HandleElectedProposer() ↓ WPS_ELECTED │ 给所有 SS_WAIT_ELECTED 发 ProposerElected │ → StartStreaming → 进入 WAL 流复制 / 心跳阶段
