performance-analysis（绩效分析）

Performance Profiling

When to Use

• Establishing performance baselines before optimization
• Diagnosing slow response times, high CPU, or memory issues
• Identifying bottlenecks in application, database, or infrastructure
• Planning capacity for expected load increases
• Validating performance improvements after optimization
• Creating performance budgets for new features

Core Methodology

The Golden Rule: Measure First

Never optimize based on assumptions. Follow this order:

1. Measure - Establish baseline metrics
2. Identify - Find the actual bottleneck
3. Hypothesize - Form a theory about the cause
4. Fix - Implement targeted optimization
5. Validate - Measure again to confirm improvement
6. Document - Record findings and decisions

Profiling Hierarchy

Profile at the right level to find the actual bottleneck:

Application Level
    |-- Request/Response timing
    |-- Function/Method profiling
    |-- Memory allocation tracking
    |
System Level
    |-- CPU utilization per process
    |-- Memory usage patterns
    |-- I/O wait times
    |-- Network latency
    |
Infrastructure Level
        |-- Database query performance
        |-- Cache hit rates
        |-- External service latency
        |-- Resource saturation

Profiling Patterns

CPU Profiling

Identify what code consumes CPU time:

1. Sampling profilers - Low overhead, statistical accuracy
2. Instrumentation profilers - Exact counts, higher overhead
3. Flame graphs - Visual representation of call stacks

Key metrics:

• Self time (time in function itself)
• Total time (self time + time in called functions)
• Call count and frequency

Memory Profiling

Track allocation patterns and detect leaks:

1. Heap snapshots - Point-in-time memory state
2. Allocation tracking - What allocates memory and when
3. Garbage collection analysis - GC frequency and duration

Key metrics:

• Heap size over time
• Object retention
• Allocation rate
• GC pause times

I/O Profiling

Measure disk and network operations:

1. Disk I/O - Read/write latency, throughput, IOPS
2. Network I/O - Latency, bandwidth, connection count
3. Database I/O - Query time, connection pool usage

Key metrics:

• Latency percentiles (p50, p95, p99)
• Throughput (ops/sec, MB/sec)
• Queue depth and wait times

Bottleneck Identification

The USE Method

For each resource, check:

• Utilization - Percentage of time resource is busy
• Saturation - Degree of queued work
• Errors - Error count for the resource

The RED Method

For services, measure:

• Rate - Requests per second
• Errors - Failed requests per second
• Duration - Distribution of request latencies

Common Bottleneck Patterns

Amdahl's Law

Optimization impact is limited by the fraction of time affected:

If 90% of time is in function A and 10% in function B:
- Optimizing A by 50% = 45% total improvement
- Optimizing B by 50% = 5% total improvement

Focus on the biggest contributors first.

Capacity Planning

Baseline Establishment

Measure current capacity under production load:

1. Peak load metrics - Maximum concurrent users, requests/sec
2. Resource headroom - How close to limits at peak
3. Scaling patterns - Linear, sub-linear, or super-linear

Load Testing Approach

1. Establish baseline - Current performance at normal load
2. Ramp testing - Gradually increase load to find limits
3. Stress testing - Push beyond limits to understand failure modes
4. Soak testing - Sustained load to find memory leaks, degradation

Capacity Metrics

Growth Planning

Required Capacity = (Current Load x Growth Factor) + Safety Margin

Example:
- Current: 1000 req/sec
- Expected growth: 50% per year
- Safety margin: 30%

Year 1 need = (1000 x 1.5) x 1.3 = 1950 req/sec

Optimization Patterns

Quick Wins

1. Enable caching - Application, CDN, database query cache
2. Add indexes - For slow queries identified in profiling
3. Compression - Gzip/Brotli for responses
4. Connection pooling - Reduce connection overhead
5. Batch operations - Reduce round-trips

Algorithmic Improvements

1. Reduce complexity - O(n^2) to O(n log n)
2. Lazy evaluation - Defer work until needed
3. Memoization - Cache computed results
4. Pagination - Limit data processed at once

Architectural Changes

1. Horizontal scaling - Add more instances
2. Async processing - Queue background work
3. Read replicas - Distribute read load
4. Caching layers - Redis, Memcached
5. CDN - Edge caching for static content

Best Practices

• Profile in production-like environments; development can have different characteristics
• Use percentiles (p95, p99) not averages for latency
• Monitor continuously, not just during incidents
• Set performance budgets and enforce them in CI
• Document baseline metrics before making changes
• Keep profiling overhead low in production
• Correlate metrics across layers (application, database, infrastructure)
• Understand the difference between latency and throughput

Anti-Patterns

• Optimizing without measurement
• Using averages for latency metrics
• Profiling only in development
• Ignoring tail latencies (p99, p999)
• Premature optimization of non-bottleneck code
• Over-engineering for hypothetical scale
• Caching without invalidation strategy

References

• Profiling Tools Reference - Tools by language and platform