diff --git a/plan_exec.md b/plan_exec.md
index 8fafd39..5045ad9 100644
--- a/plan_exec.md
+++ b/plan_exec.md
@@ -70,4 +70,24 @@
   - `cmake --build --preset release -j` 通过
   - `bash -n scripts/phase3.sh` 通过
   - `python3 -m py_compile scripts/phase3_report.py` 通过
+- 提交：`4b7c511` (`phase3: add durability mode matrix and cost report`)
+
+## Phase 4（已完成）
+- 日期：2026-03-03
+- 范围：
+  - 扩展 `src/main.rs` 与 `rocksdb/main.cpp`：
+    - 新增 `--reuse-path`（允许复用已存在数据目录）
+    - 新增 `--skip-prefill`（重启后直接用既有数据集）
+  - 新增 `scripts/phase4_soak.sh`：
+    - baseline：`tier-m + W3 + P2 + 12 threads`
+    - 周期性 `kill -9` + restart 验证（默认每 30 分钟）
+    - 记录 `restart_ready_ms` 与退出状态到 `phase4_restart.csv`
+  - 新增 `scripts/phase4_report.py`：
+    - 汇总 restart 成功率
+    - 输出 restart ready 时间分位（p50/p95/p99/max）
+- 验证：
+  - `cargo check -q` 通过
+  - `cmake --build --preset release -j` 通过
+  - `bash -n scripts/phase4_soak.sh` 通过
+  - `python3 -m py_compile scripts/phase4_report.py` 通过
 - 提交：待本阶段 commit
diff --git a/rocksdb/main.cpp b/rocksdb/main.cpp
index 6209b47..0649669 100644
--- a/rocksdb/main.cpp
+++ b/rocksdb/main.cpp
@@ -83,6 +83,8 @@ struct Args {
     std::string durability = "relaxed";
     std::string result_file = "benchmark_results.csv";
     bool cleanup = true;
+    bool skip_prefill = false;
+    bool reuse_path = false;
 };
 
 enum class Distribution {
@@ -706,6 +708,8 @@ int main(int argc, char *argv[]) {
     app.add_flag("--random", args.random, "Shuffle insert keys (legacy insert)");
     app.add_flag("--no-shared-keyspace", disable_shared, "Use per-thread keyspace");
     app.add_flag("--no-cleanup", disable_cleanup, "Keep db directory after run");
+    app.add_flag("--skip-prefill", args.skip_prefill, "Skip prefill and use existing dataset");
+    app.add_flag("--reuse-path", args.reuse_path, "Allow opening existing db path");
 
     CLI11_PARSE(app, argc, argv);
 
@@ -719,7 +723,7 @@ int main(int argc, char *argv[]) {
         fmt::println(stderr, "path is empty");
         return 1;
     }
-    if (std::filesystem::exists(args.path)) {
+    if (std::filesystem::exists(args.path) && !args.reuse_path) {
         fmt::println(stderr, "path `{}` already exists", args.path);
         return 1;
     }
@@ -809,7 +813,7 @@ int main(int argc, char *argv[]) {
 
     std::string value(args.value_size, '0');
 
-    if (workload_spec.requires_prefill) {
+    if (workload_spec.requires_prefill && !args.skip_prefill) {
         std::vector<std::thread> fill_threads;
         fill_threads.reserve(args.threads);
         for (size_t tid = 0; tid < args.threads; ++tid) {
diff --git a/scripts/phase4_report.py b/scripts/phase4_report.py
new file mode 100755
index 0000000..4612743
--- /dev/null
+++ b/scripts/phase4_report.py
@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+
+import sys
+import pandas as pd
+
+
+def main() -> int:
+    if len(sys.argv) != 2:
+        print(f"Usage: {sys.argv[0]} <restart_csv>")
+        return 1
+
+    df = pd.read_csv(sys.argv[1])
+    needed = {"cycle", "restart_status", "restart_ready_ms", "worker_exit"}
+    missing = needed - set(df.columns)
+    if missing:
+        raise ValueError(f"Missing columns: {sorted(missing)}")
+
+    total = len(df)
+    restart_ok = int((df["restart_status"] == 0).sum())
+    worker_nonzero = int((df["worker_exit"] != 0).sum())
+
+    print(f"cycles={total}")
+    print(f"restart_success={restart_ok}/{total} ({(restart_ok / total * 100.0) if total else 0.0:.1f}%)")
+    print(f"worker_nonzero_exit={worker_nonzero}/{total}")
+
+    if total:
+        q = df["restart_ready_ms"].quantile([0.5, 0.95, 0.99]).to_dict()
+        print(
+            "restart_ready_ms: "
+            f"p50={q.get(0.5, 0):.1f}, "
+            f"p95={q.get(0.95, 0):.1f}, "
+            f"p99={q.get(0.99, 0):.1f}, "
+            f"max={df['restart_ready_ms'].max():.1f}"
+        )
+
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/scripts/phase4_soak.sh b/scripts/phase4_soak.sh
new file mode 100755
index 0000000..285cb2b
--- /dev/null
+++ b/scripts/phase4_soak.sh
@@ -0,0 +1,140 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+if [ "$#" -lt 2 ] || [ "$#" -gt 4 ]; then
+    printf "Usage: %s <engine:mace|rocksdb> <db_path_under_/nvme> [result_csv] [restart_csv]\n" "$0"
+    exit 1
+fi
+
+engine="$1"
+db_path="$2"
+
+script_dir="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
+root_dir="$(cd -- "${script_dir}/.." && pwd)"
+
+result_file="${3:-${script_dir}/phase4_results.csv}"
+restart_file="${4:-${script_dir}/phase4_restart.csv}"
+
+if [[ "${db_path}" != /nvme* ]]; then
+    printf "db_path must be under /nvme, got: %s\n" "${db_path}" >&2
+    exit 1
+fi
+
+if [[ "${engine}" != "mace" && "${engine}" != "rocksdb" ]]; then
+    printf "engine must be mace or rocksdb\n" >&2
+    exit 1
+fi
+
+mkdir -p "$(dirname -- "${db_path}")"
+mkdir -p "$(dirname -- "${result_file}")"
+mkdir -p "$(dirname -- "${restart_file}")"
+
+soak_hours="${SOAK_HOURS:-12}"
+crash_interval_secs="${CRASH_INTERVAL_SECS:-1800}"
+verify_measure_secs="${VERIFY_MEASURE_SECS:-30}"
+run_measure_secs="${RUN_MEASURE_SECS:-3600}"
+warmup_secs="${WARMUP_SECS:-30}"
+
+# baseline: tier-m + W3 + P2 + 12 threads
+workload_main="W3"
+workload_verify="W6"
+threads=12
+key_size=32
+value_size=1024
+prefill_keys=18302417
+read_path="${READ_PATH:-snapshot}"
+durability="${DURABILITY:-relaxed}"
+
+start_epoch="$(date +%s)"
+end_epoch="$((start_epoch + soak_hours * 3600))"
+
+run_cmd() {
+    local workload="$1"
+    local measure_secs="$2"
+    local skip_prefill="$3"
+
+    if [ "${engine}" = "mace" ]; then
+        local cleanup_flag
+        cleanup_flag="false"
+        "${root_dir}/target/release/kv_bench" \
+          --path "${db_path}" \
+          --workload "${workload}" \
+          --threads "${threads}" \
+          --key-size "${key_size}" \
+          --value-size "${value_size}" \
+          --prefill-keys "${prefill_keys}" \
+          --warmup-secs "${warmup_secs}" \
+          --measure-secs "${measure_secs}" \
+          --shared-keyspace true \
+          --read-path "${read_path}" \
+          --durability "${durability}" \
+          --cleanup "${cleanup_flag}" \
+          --reuse-path \
+          $( [ "${skip_prefill}" = "1" ] && printf '%s' "--skip-prefill" ) \
+          --result-file "${result_file}"
+    else
+        "${root_dir}/rocksdb/build/release/rocksdb_bench" \
+          --path "${db_path}" \
+          --workload "${workload}" \
+          --threads "${threads}" \
+          --key-size "${key_size}" \
+          --value-size "${value_size}" \
+          --prefill-keys "${prefill_keys}" \
+          --warmup-secs "${warmup_secs}" \
+          --measure-secs "${measure_secs}" \
+          --read-path "${read_path}" \
+          --durability "${durability}" \
+          --no-cleanup \
+          --reuse-path \
+          $( [ "${skip_prefill}" = "1" ] && printf '%s' "--skip-prefill" ) \
+          --result-file "${result_file}"
+    fi
+}
+
+if [ ! -f "${restart_file}" ]; then
+    printf "cycle,start_epoch,kill_sent,worker_exit,restart_status,restart_ready_ms\n" > "${restart_file}"
+fi
+
+# seed dataset once (with prefill)
+printf "[phase4][%s] seed dataset at %s\n" "${engine}" "${db_path}"
+run_cmd "${workload_main}" 5 0
+
+cycle=0
+while [ "$(date +%s)" -lt "${end_epoch}" ]; do
+    cycle="$((cycle + 1))"
+    cycle_start="$(date +%s)"
+    printf "[phase4][%s] cycle=%s start=%s\n" "${engine}" "${cycle}" "${cycle_start}"
+
+    # long run in background; kill after interval
+    (run_cmd "${workload_main}" "${run_measure_secs}" 1) &
+    runner_pid=$!
+
+    sleep "${crash_interval_secs}"
+
+    kill_sent=0
+    if kill -0 "${runner_pid}" 2>/dev/null; then
+        kill -9 "${runner_pid}" || true
+        kill_sent=1
+    fi
+
+    set +e
+    wait "${runner_pid}"
+    worker_exit=$?
+    set -e
+
+    restart_start_ms="$(date +%s%3N)"
+    restart_status=0
+    set +e
+    run_cmd "${workload_verify}" "${verify_measure_secs}" 1
+    restart_status=$?
+    set -e
+    restart_end_ms="$(date +%s%3N)"
+    restart_ready_ms="$((restart_end_ms - restart_start_ms))"
+
+    printf "%s,%s,%s,%s,%s,%s\n" \
+      "${cycle}" "${cycle_start}" "${kill_sent}" "${worker_exit}" "${restart_status}" "${restart_ready_ms}" >> "${restart_file}"
+done
+
+python3 "${script_dir}/phase4_report.py" "${restart_file}"
+printf "Phase 4 soak finished. Results: %s | Restart log: %s\n" "${result_file}" "${restart_file}"
diff --git a/src/main.rs b/src/main.rs
index 674f542..0cdd9b2 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -86,6 +86,12 @@ struct Args {
 
     #[arg(long, default_value_t = true)]
     cleanup: bool,
+
+    #[arg(long, default_value_t = false)]
+    skip_prefill: bool,
+
+    #[arg(long, default_value_t = false)]
+    reuse_path: bool,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
@@ -619,7 +625,7 @@ fn main() {
         eprintln!("path is empty");
         exit(1);
     }
-    if path.exists() {
+    if path.exists() && !args.reuse_path {
         eprintln!("path {:?} already exists", args.path);
         exit(1);
     }
@@ -700,10 +706,16 @@ fn main() {
 
     let db = Mace::new(opt.validate().unwrap()).unwrap();
     db.disable_gc();
-    let bkt = db.new_bucket("default").unwrap();
+    let bkt = if args.reuse_path {
+        db.get_bucket("default")
+            .or_else(|_| db.new_bucket("default"))
+            .unwrap()
+    } else {
+        db.new_bucket("default").unwrap()
+    };
     let value = Arc::new(vec![b'0'; args.value_size]);
 
-    if workload.requires_prefill {
+    if workload.requires_prefill && !args.skip_prefill {
         let mut fill_handles = Vec::with_capacity(args.threads);
         for tid in 0..args.threads {
             let bucket = bkt.clone();