From b273390ce76c7df06ff94124495fde89e283689a Mon Sep 17 00:00:00 2001
From: bang <3656828039@qq.com>
Date: Mon, 1 Jun 2026 19:31:40 +0800
Subject: [PATCH] =?UTF-8?q?perf(raft):=20WAL=20=E6=89=B9=E9=87=8F=20fsync?=
 =?UTF-8?q?=20(group=20commit),=20=E6=91=8A=E9=94=80=E6=95=B4=E6=89=B9=20N?=
 =?UTF-8?q?=20=E6=AC=A1=20fsync=20=E4=B8=BA=201=20=E6=AC=A1?=
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RaftWAL.AppendLog 此前每条 entry 一次 file.Sync(), follower 端
AppendEntries 处理一整批 N 条时循环调用 → N 次 fsync; rebuild/
SavePersist 同样逐条 fsync。

拆出 writeEntry(只写不 sync), AppendLog = writeEntry + Sync 不变;
新增 AppendLogs(entries): 全部写完只 fsync 一次。rpc.go follower
批量循环及 TruncateLogs/RebuildLogFile/SavePersist 改用 AppendLogs。

durability 契约不变: 整批写入仍在 persistStateLocked/回复成功前落盘。
空批次为 no-op。leader 单条路径 (raft.go AppendEntry) 不变。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 Raft/raft_wal.go | 41 ++++++++++++++++++++++++++++-------------
 Raft/rpc.go      |  6 ++----
 2 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/Raft/raft_wal.go b/Raft/raft_wal.go
index a7257b7..dee5163 100644
--- a/Raft/raft_wal.go
+++ b/Raft/raft_wal.go
@@ -130,7 +130,8 @@ func (w *RaftWAL) LoadState() (int64, int64, error) {
 	return term, votedFor, nil
 }
 
-func (w *RaftWAL) AppendLog(entry LogEntry) error {
+// writeEntry 写入单条日志的字节，但不 fsync。供 AppendLog 与 AppendLogs 复用。
+func (w *RaftWAL) writeEntry(entry LogEntry) error {
 	if err := binary.Write(w.file, binary.BigEndian, int64(entry.Index)); err != nil {
 		return err
 	}
@@ -143,7 +144,27 @@ func (w *RaftWAL) AppendLog(entry LogEntry) error {
 	if _, err := w.file.Write(entry.Command); err != nil {
 		return err
 	}
+	return nil
+}
+
+func (w *RaftWAL) AppendLog(entry LogEntry) error {
+	if err := w.writeEntry(entry); err != nil {
+		return err
+	}
+	return w.file.Sync()
+}
 
+// AppendLogs 批量追加日志：全部写完后只 fsync 一次（group commit），
+// 将整批 N 条的 N 次 fsync 摊销为 1 次。空批次为 no-op。
+func (w *RaftWAL) AppendLogs(entries []LogEntry) error {
+	if len(entries) == 0 {
+		return nil
+	}
+	for _, entry := range entries {
+		if err := w.writeEntry(entry); err != nil {
+			return err
+		}
+	}
 	return w.file.Sync()
 }
 
@@ -372,10 +393,8 @@ func (w *RaftWAL) TruncateLogs(lastIncludedIndex int64) error {
 	}
 	w.file = f
 
-	for _, log := range remainingLogs {
-		if err := w.AppendLog(log); err != nil {
-			return err
-		}
+	if err := w.AppendLogs(remainingLogs); err != nil {
+		return err
 	}
 
 	return nil
@@ -391,10 +410,8 @@ func (w *RaftWAL) RebuildLogFile(entries []LogEntry) error {
 	}
 	w.file = f
 
-	for _, entry := range entries {
-		if err := w.AppendLog(entry); err != nil {
-			return fmt.Errorf("failed to append log entry: %w", err)
-		}
+	if err := w.AppendLogs(entries); err != nil {
+		return fmt.Errorf("failed to append log entries: %w", err)
 	}
 	return nil
 }
@@ -416,10 +433,8 @@ func (w *RaftWAL) SavePersist(data PersistData) error {
 	w.file = f
 
 	// 3. 写入所有日志条目
-	for _, entry := range data.Log {
-		if err := w.AppendLog(entry); err != nil {
-			return fmt.Errorf("failed to append log entry: %w", err)
-		}
+	if err := w.AppendLogs(data.Log); err != nil {
+		return fmt.Errorf("failed to append log entries: %w", err)
 	}
 
 	return nil
diff --git a/Raft/rpc.go b/Raft/rpc.go
index 838040b..75700dc 100644
--- a/Raft/rpc.go
+++ b/Raft/rpc.go
@@ -174,10 +174,8 @@ func (r *RaftRPC) AppendEntries(args *AppendEntriesArgs, reply *AppendEntriesRep
 				slog.Error("failed to rebuild log", "error", err)
 			}
 		} else {
-			for _, entry := range newEntries {
-				if err := r.raft.wal.AppendLog(entry); err != nil {
-					slog.Error("failed to append log", "error", err)
-				}
+			if err := r.raft.wal.AppendLogs(newEntries); err != nil {
+				slog.Error("failed to append logs", "error", err)
 			}
 		}
 		r.raft.persistStateLocked()