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.teamai/skills/common/golang-troubleshooting/references/performance-debug.md

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+# Performance Troubleshooting
+
+## CPU Profiling
+
+Use pprof CPU profile to capture a 30s sample (see [pprof.md](./pprof.md) for commands), then inspect with `top`, `web`, or `list funcName`.
+
+**Common CPU hogs:**
+
+1. JSON marshal/unmarshal in hot path — preallocate buffers, use faster libraries
+2. Reflection in critical path
+3. Unnecessary allocations — use sync.Pool
+4. O(n^2) hidden in nested loops
+5. Too many syscalls — batch operations
+
+## Memory Profiling
+
+Use pprof heap profile (see [pprof.md](./pprof.md)). Compare heap snapshots over time with `go tool pprof -base heap1.prof heap2.prof` to find growth. Use escape analysis (see [diagnostic-tools.md](./diagnostic-tools.md)) to find unexpected heap allocations in hot paths.
+
+**Common memory leaks:**
+
+1. Unbounded cache without eviction
+2. Growing slices in loops (forgetting to reset)
+3. Global maps never cleared
+4. String concatenation in loops (use `strings.Builder`)
+5. Large structs passed by value
+
+## Lock Contention
+
+**Symptoms:** CPU high but throughput low, latency increases with load, multiple cores don't help.
+
+**Enable profiling in code:**
+
+```go
+runtime.SetMutexProfileFraction(1)
+runtime.SetBlockProfileRate(1)
+```
+
+Then use pprof mutex and block profiles (see [pprof.md](./pprof.md)).
+
+**Solutions:**
+
+1. Reduce critical section — hold lock for minimal time
+2. Sharding — multiple locks for different data
+3. `sync.Map` — for read-heavy workloads
+4. `atomic` — for simple counters
+5. `RWMutex` — when reads >> writes