High memory usage: 5.9GB external ArrayBuffers within 26 seconds of startup

Summary

Claude Code v2.1.73 (also reproduced on v2.1.74) exhibits high memory usage immediately after startup. A manual /heapdump taken 26 seconds into a fresh session shows ~6.5 GB heap used, with 5.9 GB in external ArrayBuffers.

Environment

• Platform: Windows 11 Home (win32) 10.0.26200
• Node: v24.3.0
• Claude Code: 2.1.73 (current session), 2.1.74 installed
• Shell: bash (Git Bash)
• Project: UE5 C++ project (~4.4 GB on disk, .gitignore excludes binaries/intermediate)
• Memory files: 225 MB of session transcripts (143 .jsonl files), 36 KB of memory .md files

Diagnostics (from /heapdump)

{
  "uptimeSeconds": 26.29,
  "memoryUsage": {
    "heapUsed": 6495827413,
    "heapTotal": 51532800,
    "external": 6459777423,
    "arrayBuffers": 5929917893,
    "rss": 2012729344
  },
  "memoryGrowthRate": {
    "bytesPerSecond": 76559969,
    "mbPerHour": 262847
  }
}

Heap Snapshot Analysis

The V8 heap itself is healthy (~62 MB across all object types):

• Code: 21.3 MB
• Objects: 19.6 MB
• Native: 9.7 MB
• Closures: 5.6 MB
• Strings: 3.6 MB

The problem is entirely in external/native memory (5.9 GB ArrayBuffers) which V8's heap snapshot does not break down further.

Identified allocations (small, expected)

• 16 MB ArrayBuffer → WebAssembly.Memory (tree-sitter WASM)
• ~10 MB across 6 Blob objects (tree-sitter language grammars)
• Two WASM modules: tree-sitter + yoga-layout (yoga-wasm-base64-esm.js)

Unaccounted

• ~5.87 GB of external ArrayBuffers with no V8-visible owner
• Growth rate of 73 MB/sec suggests continuous allocation without release

Reproduction

1. Open Claude Code in a project with ~100+ prior session transcripts
2. Run /heapdump immediately after startup
3. Observe external memory far exceeding V8 heap

Hypothesis

The external ArrayBuffer growth pattern (73 MB/sec, linear) suggests streaming buffers (possibly API response chunks or file read buffers) are being allocated but not freed. The native memory is invisible to V8 GC, pointing to a leak in:

• Streaming API response handling (fetch/undici body buffers)
• File read operations during startup (context loading, CLAUDE.md, rules, memory)
• Session transcript processing (143 .jsonl files totaling 225 MB)

Attached

Heap snapshot and diagnostics JSON were saved locally. Happy to provide if needed.

🤖 Generated with Claude Code