From 8996e82d84dad9e1f0cd574f786c11960f842adf Mon Sep 17 00:00:00 2001
From: bang <3656828039@qq.com>
Date: Tue, 12 May 2026 00:55:03 +0800
Subject: [PATCH] =?UTF-8?q?fix(storage):=20Delete=20=E5=86=99=E5=85=A5=20W?=
 =?UTF-8?q?AL=20tombstone=20=E7=A1=AE=E4=BF=9D=E5=B4=A9=E6=BA=83=E6=81=A2?=
 =?UTF-8?q?=E5=A4=8D=E6=97=B6=E8=83=BD=E9=87=8D=E6=94=BE=E5=88=A0=E9=99=A4?=
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Delete 之前未写 WAL,崩溃恢复时会丢失已删除的 key。
修复: 在删除前先写 WAL(nil value = tombstone),
恢复时遇到 nil value 则执行 delete 而非 insert,保持与 Put 一致的错误处理流程。
---
 storage/zstorage/memtable.go | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/storage/zstorage/memtable.go b/storage/zstorage/memtable.go
index 290a16a..61a8838 100644
--- a/storage/zstorage/memtable.go
+++ b/storage/zstorage/memtable.go
@@ -227,6 +227,12 @@ func (m *MemTable) Delete(key []byte) error {
 		return errors.New("NO DATA IN MEMTABLE")
 	}
 
+	// 先写 WAL tombstone（value 为 nil 表示删除标记），确保崩溃恢复时能重放删除
+	if err := m.wal.Write(istorage.LogEntry{Key: key, Value: nil}); err != nil {
+		fmt.Println("Error writing delete to WAL:", err)
+		return err
+	}
+
 	if !m.active.delete(key) {
 		fmt.Println("the key does not exist")
 		return errors.New("KEY NOT FOUND")
@@ -281,8 +287,11 @@ func (m *MemTable) recoverFromWAL() {
 	fmt.Printf("[INFO] Recovering %d entries from WAL...\n", len(entries))
 
 	for _, entry := range entries {
-		// 直接插入 active 表，不写入 WAL（避免重复写入）
-		m.active.insert(entry.Key, entry.Value)
+		if entry.Value == nil {
+			m.active.delete(entry.Key)
+		} else {
+			m.active.insert(entry.Key, entry.Value)
+		}
 	}
 
 	fmt.Printf("[INFO] WAL recovery completed, memtable size: %d\n", m.active.size)