nextjs - 💡(How to fix) Fix Memory leak (ArrayBuffer/WriteWrap retention) in Next.js 16.1.6 stable — fixed in canary but not released [1 comments, 2 participants]

Link to the code that reproduces this issue

Reproduction was done on our private production app, but the issue matches existing reports in #85914, #89033, #90433.

To Reproduce

1. Create a Next.js app with output: 'standalone', deploy on ARM64 (AWS ECS Fargate with Graviton)
2. Send traffic to any API routes or pages that go through the Next.js response pipeline
3. Monitor process.memoryUsage().arrayBuffers via a health endpoint

Current vs. Expected behavior

Current (16.1.6 stable): ArrayBuffers grow linearly at ~5 MB/s and are never reclaimed, even with --expose-gc and manual global.gc(). OOM kill within 10 minutes.

Expected: Memory should stabilize and be reclaimed by GC after requests complete.

Evidence

Memory timeline on 16.1.6 (stable) — leaks

Memory timeline on 16.2.0-canary.79 — fixed

Heap dump analysis (captured at 1008 MB ArrayBuffers)

977 MB retained across 183 JSArrayBufferData objects. Retainer chains:

JSArrayBufferData (32 MB)
  ← ArrayBuffer
    ← Buffer
      ← Array[4]
        ← WriteWrap._chunks     ← pinned to GC roots (Global handles)

20 of 31 large ArrayBuffers (>30MB) retained by WriteWrap._chunks (Node.js native HTTP write wrappers). 5 of 31 retained by circular Generator chains (async stream iteration).

Root cause

Three bugs in Next.js 16.1.6 interact to cause unbounded ArrayBuffer growth:

1. clone-response.js: Only cloned1 is registered with FinalizationRegistry, not cloned2. Since cloned2 is stored in caches, its underlying tee buffer (backed by ArrayBuffers) is never auto-cancelled. Fixed in #88577.

2. cache-handlers/default.js: Empty ReadableStream bodies get size = 0 in the LRU cache. Zero-size entries never trigger eviction (totalSize never exceeds maxSize), causing unbounded Map growth. Fixed in #89040.

3. Response pipeline retention: sendResponse → pipeToNodeResponse creates WriteWrap objects via res.write(chunk) that are pinned to GC roots. Without the FinalizationRegistry fix, the source ReadableStreams (tee branches) are never cancelled, keeping the write buffers alive indefinitely. Partially addressed in #90771.

Fix confirmation

All three fixes are present in [email protected]. We confirmed the leak is completely resolved on canary — ArrayBuffers return to baseline (32 MB) after load stops.

However, none of these fixes are in any 16.x stable release (latest is 16.1.6). PR #89040 was backported to 15.5.11, but the 16.x branch has not received it.

Request

Please release a 16.x stable version that includes PRs #88577, #89040, and #90771. This is a critical production issue causing OOM kills for anyone using output: 'standalone' with server-side fetch on Next.js 16.

Provide environment information

Platform: linux (AWS ECS Fargate, ARM64 Graviton)
Node: v22.22.0
Next.js: 16.1.6 (leaks) → 16.2.0-canary.79 (fixed)
output: standalone
compress: false (offloaded to ALB)

Which area(s) are affected?

Performance, Runtime

Which stage(s) are affected?

Other (Deployed, production)