8 files changed, 73 insertions, 31 deletions
diff --git a/.changeset/fifty-icons-smash.md b/.changeset/fifty-icons-smash.md
new file mode 100644
index 000000000..29dcc6354
--- /dev/null
+++ b/.changeset/fifty-icons-smash.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix perf regression in SSR
diff --git a/packages/astro/src/runtime/server/render/common.ts b/packages/astro/src/runtime/server/render/common.ts
index e64a18189..421546a46 100644
--- a/packages/astro/src/runtime/server/render/common.ts
+++ b/packages/astro/src/runtime/server/render/common.ts
@@ -45,35 +45,22 @@ export function stringifyChunk(result: SSRResult, chunk: string | RenderInstruct
 }
 
 export class HTMLParts {
-	public parts: Array<HTMLBytes | string>;
+	public parts: string;
 	constructor() {
-		this.parts = [];
+		this.parts = ''
 	}
 	append(part: string | HTMLBytes | RenderInstruction, result: SSRResult) {
 		if (ArrayBuffer.isView(part)) {
-			this.parts.push(part);
+			this.parts += decoder.decode(part);
 		} else {
-			this.parts.push(stringifyChunk(result, part));
+			this.parts += stringifyChunk(result, part);
 		}
 	}
 	toString() {
-		let html = '';
-		for (const part of this.parts) {
-			if (ArrayBuffer.isView(part)) {
-				html += decoder.decode(part);
-			} else {
-				html += part;
-			}
-		}
-		return html;
+		return this.parts;
 	}
 	toArrayBuffer() {
-		this.parts.forEach((part, i) => {
-			if (!ArrayBuffer.isView(part)) {
-				this.parts[i] = encoder.encode(String(part));
-			}
-		});
-		return concatUint8Arrays(this.parts as Uint8Array[]);
+		return encoder.encode(this.parts);
 	}
 }
 
@@ -86,15 +73,3 @@ export function chunkToByteArray(
 	}
 	return encoder.encode(stringifyChunk(result, chunk));
 }
-
-export function concatUint8Arrays(arrays: Array<Uint8Array>) {
-	let len = 0;
-	arrays.forEach((arr) => (len += arr.length));
-	let merged = new Uint8Array(len);
-	let offset = 0;
-	arrays.forEach((arr) => {
-		merged.set(arr, offset);
-		offset += arr.length;
-	});
-	return merged;
-}
diff --git a/packages/astro/test/benchmark/simple/astro.config.mjs b/packages/astro/test/benchmark/simple/astro.config.mjs
new file mode 100644
index 000000000..da503f3ba
--- /dev/null
+++ b/packages/astro/test/benchmark/simple/astro.config.mjs
@@ -0,0 +1,7 @@
+import { defineConfig } from 'astro/config';
+import nodejs from '@astrojs/node';
+
+export default defineConfig({
+	output: 'server',
+	adapter: nodejs()
+});
diff --git a/packages/astro/test/benchmark/simple/package.json b/packages/astro/test/benchmark/simple/package.json
new file mode 100644
index 000000000..d54f76f90
--- /dev/null
+++ b/packages/astro/test/benchmark/simple/package.json
@@ -0,0 +1,11 @@
+{
+  "name": "@benchmark/simple",
+  "scripts": {
+    "start": "node server.mjs",
+    "build": "astro build"
+  },
+  "dependencies": {
+    "astro": "workspace:*",
+    "@astrojs/node": "workspace:*"
+  }
+}
diff --git a/packages/astro/test/benchmark/simple/server.mjs b/packages/astro/test/benchmark/simple/server.mjs
new file mode 100644
index 000000000..e5844d60c
--- /dev/null
+++ b/packages/astro/test/benchmark/simple/server.mjs
@@ -0,0 +1,19 @@
+import http from 'http';
+import { handler } from './dist/server/entry.mjs';
+
+const listener = (req, res) => {
+	handler(req, res, err => {
+		if(err) {
+			res.writeHead(500);
+			res.end(err.toString());
+		} else {
+			res.writeHead(404);
+			res.end('Not found');
+		}
+	});
+};
+
+const server = http.createServer(listener);
+server.listen(3002);
+// eslint-disable-next-line no-console
+console.log(`Listening at http://localhost:3002`);
diff --git a/packages/astro/test/benchmark/simple/src/components/Layout.astro b/packages/astro/test/benchmark/simple/src/components/Layout.astro
new file mode 100644
index 000000000..c8a65f26e
--- /dev/null
+++ b/packages/astro/test/benchmark/simple/src/components/Layout.astro
@@ -0,0 +1,8 @@
+<html>
+	<head>
+		<title>{ Astro.props.title }</title>
+	</head>
+	<body>
+		<slot />
+	</body>
+</html>
diff --git a/packages/astro/test/benchmark/simple/src/pages/index.astro b/packages/astro/test/benchmark/simple/src/pages/index.astro
new file mode 100644
index 000000000..ee287144f
--- /dev/null
+++ b/packages/astro/test/benchmark/simple/src/pages/index.astro
@@ -0,0 +1,9 @@
+---
+import Layout from '../components/Layout.astro';
+const name = 'world';
+---
+
+<Layout title={`Index page`}>
+	<h1>index page</h1>
+	<h2>Hello { name }</h2>
+</Layout>
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 9d1fdfcd8..0e906a047 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -1055,6 +1055,14 @@ importers:
       astro: link:../../..
       vue: 3.2.40
 
+  packages/astro/test/benchmark/simple:
+    specifiers:
+      '@astrojs/node': workspace:*
+      astro: workspace:*
+    dependencies:
+      '@astrojs/node': link:../../../../integrations/node
+      astro: link:../../..
+
   packages/astro/test/fixtures/0-css:
     specifiers:
       '@astrojs/react': workspace:*