Serialize exports to prevent OOM spikes from stacking

/api/export-excel now holds a per-process mutex: concurrent callers get an
instant 429 instead of stacking multiple ~1.3GB export spikes that exceed
Node's default ~2GB heap. Frontend handleExport treats 429 as 'another
export running' and auto-retries (3s backoff, up to 7 attempts). A 90s
timeout reclaims a stuck lock. Heap raise + orphan cleanup applied at deploy.

Co-Authored-By: Claude <noreply@anthropic.com>

src/app/api/export-excel/route.ts

@@ -41,7 +41,40 @@ const DATE_COLUMNS = new Set([
   "烘洗",
 ]);
 
+/*
+ * Serialize exports. A single export of the full dataset (~33k rows) peaks at
+ * ~1.3GB heap; letting two run at once would exceed Node's default ~2GB heap
+ * and OOM the server. All /api/export-excel requests are handled by the one
+ * Next server process (the listener on the port), so a module-level flag
+ * correctly serializes concurrent requests: the 2nd+ callers get an instant
+ * 429 and the frontend retries. Memory peak is capped at one export at a time.
+ */
+let exportLocked = false;
+let exportLockedAt = 0;
+const EXPORT_LOCK_TIMEOUT_MS = 90_000; // safety: reclaim a stuck lock after 90s
+
+function acquireExportLock(): boolean {
+  if (exportLocked && Date.now() - exportLockedAt > EXPORT_LOCK_TIMEOUT_MS) {
+    console.warn("Export lock reclaimed after timeout");
+    exportLocked = false;
+  }
+  if (exportLocked) return false;
+  exportLocked = true;
+  exportLockedAt = Date.now();
+  return true;
+}
+
+function releaseExportLock() {
+  exportLocked = false;
+}
+
 export async function GET() {
+  if (!acquireExportLock()) {
+    return NextResponse.json(
+      { error: "正在导出，请稍候" },
+      { status: 429, headers: { "Retry-After": "3" } }
+    );
+  }
   let pool: sql.ConnectionPool | undefined;
   try {
     pool = await sql.connect(dbConfig);
@@ -136,5 +169,6 @@ export async function GET() {
     if (pool) {
       await pool.close();
     }
+    releaseExportLock();
   }
 }

src/app/page.tsx

@@ -542,8 +542,15 @@ export default function Home() {
 
   const handleExport = useCallback(async () => {
     setExporting(true);
+    setError(null);
     try {
+      const MAX_ATTEMPTS = 7; // 429 = 另有人在导出，退避后自动重试
+      for (let attempt = 1; attempt <= MAX_ATTEMPTS; attempt++) {
         const res = await fetch("/api/export-excel");
+        if (res.status === 429) {
+          await new Promise((r) => setTimeout(r, 3000));
+          continue;
+        }
         if (!res.ok) {
           const json = await res.json().catch(() => null);
           setError(json?.error || "导出失败");
@@ -558,6 +565,9 @@ export default function Home() {
         a.click();
         document.body.removeChild(a);
         URL.revokeObjectURL(url);
+        return;
+      }
+      setError("导出繁忙，请稍后重试");
     } catch {
       setError("导出请求失败");
     } finally {