Memory Profiling for Sidecar

Quick Triage

Triage flow: Is RSS high? -> Check FD count -> Check vmmap -> Check heap profile

System-Level Profiling (No pprof Required)

Find the Process

pgrep -f sidecar
ps aux | grep sidecar

Basic Stats

# RSS, VSZ, CPU%, thread count
ps -o pid,rss,vsz,%cpu,nlwp -p <PID>

# Human-readable RSS
ps -o pid,rss -p <PID> | awk 'NR>1{printf "%d MB\n", $2/1024}'

# Watch over time
while true; do ps -o rss,%cpu -p <PID> | tail -1; sleep 5; done

System Memory

macOS (vmmap):

vmmap --summary <PID>

Key sections: VM_ALLOCATE (Go heap), MALLOC (C heap/SQLite), Physical footprint, Swapped.

Red flags:

• RESIDENT SIZE >500MB for idle sidecar
• REGION COUNT in thousands for VM_ALLOCATE = mmap leak
• SWAPPED SIZE growing = memory pressure

Linux:

cat /proc/<PID>/status | grep -E 'VmRSS|VmSize|Threads'
pmap -x <PID> | tail -5
ls /proc/<PID>/fd | wc -l

File Descriptor Analysis

# Count and breakdown
lsof -p <PID> | wc -l
lsof -p <PID> | awk '{print $5}' | sort | uniq -c | sort -rn

# Find leaked files
lsof -p <PID> | grep REG | awk '{print $9}' | sort | uniq -c | sort -rn | head -20

# Check session file leaks
lsof -p <PID> | grep -c '\.claude/projects'
lsof -p <PID> | grep -c '\.codex/sessions'

# Watch FD count
while true; do echo "$(date): $(lsof -p <PID> 2>/dev/null | wc -l) FDs"; sleep 30; done

Healthy baselines: Total FDs 50-150, REG files 10-30, PIPEs 10-30, DIRs 5-15.

Red flags: 1000+ total FDs, same file opened 4+ times, growing count over time.

Thread Count

# macOS
ps -M -p <PID> | wc -l
# Linux
ls /proc/<PID>/task | wc -l
# Expected: 20-60 threads. 100+ = goroutine leak likely

Go pprof (Runtime Profiling)

Enable pprof

SIDECAR_PPROF=1 sidecar        # Default port 6060
SIDECAR_PPROF=6061 sidecar     # Custom port

Heap Profile (Current Allocations)

curl http://localhost:6060/debug/pprof/heap > heap.prof
go tool pprof -top heap.prof
go tool pprof heap.prof   # Interactive: top20, list <func>, web

Allocs Profile (All Allocations Since Start)

curl http://localhost:6060/debug/pprof/allocs > allocs.prof
go tool pprof -top allocs.prof

Goroutine Profile

# Count
curl -s http://localhost:6060/debug/pprof/goroutine?debug=1 | head -1

# Full stacks
curl http://localhost:6060/debug/pprof/goroutine?debug=2 > goroutines.txt

# Find stuck goroutines
grep -A5 'runtime.chanrecv' goroutines.txt

Memory Stats

curl http://localhost:6060/debug/pprof/heap?debug=1 | head -30

Compare Snapshots (Best for Finding Leaks)

curl http://localhost:6060/debug/pprof/heap > heap1.prof
# Wait (1 hour or overnight)
curl http://localhost:6060/debug/pprof/heap > heap2.prof
go tool pprof -base heap1.prof heap2.prof
# Then: top20

Continuous Monitoring

./scripts/mem-monitor.sh         # Default: port 6060, 60s interval
./scripts/mem-monitor.sh 6061 30 # Custom port and interval

Output: CSV time,heap_alloc_bytes,heap_inuse_bytes,goroutines,rss_mb to mem-YYYYMMDD-HHMMSS.log.

CPU Profile

curl http://localhost:6060/debug/pprof/profile?seconds=30 > cpu.prof
go tool pprof -top cpu.prof
go tool pprof cpu.prof   # Interactive: top20, list <func>, web

Web UI

go tool pprof -http=:8080 http://localhost:6060/debug/pprof/heap

Requires Graphviz (brew install graphviz / apt install graphviz) for flame graphs.

What to Look For

Goroutine leaks: Count should stabilize at 20-50 after startup. Steady growth = leak. Search for runtime.chanrecv1, runtime.chansend1, time.Sleep.

Heap growth: HeapAlloc should stabilize after loading sessions. Consistent upward trend = leak.

Common pprof signatures: bufio.Scanner (buffer not returned), json.Unmarshal (large objects retained), append in loops (slice growing), channel operations (blocked senders/receivers).

Diagnosing Unresponsive Plugins

1. Check goroutines for blocked operations:
   bashCopy

   curl -s http://localhost:6060/debug/pprof/goroutine?debug=2 | grep -A10 'monitor\|td'
   

2. Check SQLite locks: lsof -p <PID> | grep '\.db'
3. Check stuck tea.Cmd goroutines:
   bashCopy

   curl -s http://localhost:6060/debug/pprof/goroutine?debug=2 | grep -B2 'fetchData\|FetchData'
   

4. Check for swap pressure: vmmap --summary <PID> | grep -E 'Physical|Swapped'

Common causes: SQLite locked by concurrent td CLI, memory pressure causing swap thrashing, goroutine blocked on unread channel, accumulating fetchData() goroutines.

Known Leak Patterns

File Descriptor Accumulation (Adapter/Watcher Layer)

Files: internal/adapter/claudecode/watcher.go etc. Uses fsnotify to watch directories.

Symptoms: RSS grows to 5-15GB overnight, lsof shows 1000+ session files open.

lsof -p <PID> | grep '\.claude/projects' | wc -l
lsof -p <PID> | grep '\.codex/sessions' | wc -l

OutputBuffer Substring Retention

OutputBuffer.Update() uses strings.Split() creating substrings sharing backing array. NOT a leak if Update() keeps being called. Only retains if polling stops.

Poll Chain Duplication

Entering interactive mode without incrementing generation counter creates parallel poll chains. Doubles CPU but no memory leak. Fix: increment shellPollGeneration or pollGeneration on entry.

Go MADV_FREE (macOS)

Go runtime uses MADV_FREE marking pages reusable without returning to OS. RSS appears high but memory is available. NOT a leak. Use vmmap --summary and compare "Physical footprint (peak)" vs current.

Investigation Workflow

1. ps -o pid,rss,%cpu -p <PID> -- establish baseline
2. lsof -p <PID> | wc -l -- if >200, focus on FD leak
3. lsof -p <PID> | grep REG | awk '{print $9}' | sort | uniq -c | sort -rn | head -20
4. vmmap --summary <PID> -- RESIDENT vs VIRTUAL, region count
5. If pprof available: heap snapshot comparison over time
6. If pprof unavailable: restart with SIDECAR_PPROF=1, reproduce the leak

Overnight Test Procedure

1. Start: SIDECAR_PPROF=1 sidecar
2. Baseline: curl .../heap > baseline.prof
3. Note goroutine count
4. Leave overnight (caffeinate -i on macOS)
5. Morning: capture new profiles
6. Compare: go tool pprof -base baseline.prof morning.prof
7. Check goroutines for stuck ones

Notes

• pprof adds ~1-2MB overhead, no TUI performance impact
• HTTP server runs in separate goroutine, localhost only
• On macOS, vmmap/lsof need no special permissions for own processes