majiayu000 Performance Debug
Diagnose CPU, memory, disk, and network performance bottlenecks.
Instructions
- Get system overview:
top,htop, orvmstat - Identify the bottleneck type (CPU, memory, disk, network)
- Drill down with specific tools
- Identify the root cause process/resource
- Recommend solutions
Quick overview
# System summary
uptime
free -h
df -h
top -bn1 | head -20
# All-in-one view
htop # or top
CPU analysis
# High-level CPU usage
mpstat 1 5
top -bn1 -o %CPU | head -15
# Per-process CPU
pidstat 1 5
ps aux --sort=-%cpu | head -10
# Find CPU-intensive process
top -bn1 | grep -A10 "PID USER"
Memory analysis
# Memory overview
free -h
vmstat 1 5
# Per-process memory
ps aux --sort=-%mem | head -10
pidstat -r 1 5
# Memory details
cat /proc/meminfo
smem -tk # if available
# Find memory leaks (growth over time)
watch -n 5 'ps aux --sort=-%mem | head -10'
Disk analysis
# Disk space
df -h
du -sh /* 2>/dev/null | sort -hr | head -10
# Disk I/O
iostat -x 1 5
iotop -b -n 5 # requires root
# Find large files
find / -type f -size +100M 2>/dev/null
# Find disk-heavy processes
pidstat -d 1 5
Network analysis
# Connections and bandwidth
ss -tuln
ss -tunap | grep ESTAB
nethogs # per-process bandwidth
# Network statistics
netstat -i
ip -s link
# Check for connection issues
ping -c 4 8.8.8.8
mtr --report google.com
Common bottlenecks
| Symptom | Indicator | Solution |
|---|---|---|
| Load > cores | CPU-bound | Identify hot process, scale horizontally |
| High %wa in top | I/O wait | Check disk, move to SSD, optimize queries |
| Low free + high swap | Memory | Find leak, increase RAM, tune OOM |
| High %si/%hi | Interrupts | NIC issue, driver problem |
Rules
- MUST check all four resources (CPU, memory, disk, network)
- MUST identify specific processes causing issues
- MUST provide actionable recommendations
- Never kill processes without user approval
- Always check if symptoms correlate with specific times (cron, traffic)