# Memory Leak Troubleshooting Guide

**Last Updated**: 2025-10-22
**Target**: Stable memory usage over 24 hours

---

## Diagnosis

### Step 1: Identify Memory Growth

```bash
# Monitor memory usage over time
kubectl top pods -n foxhunt -l app.kubernetes.io/component=trading-service --watch

# Check memory metrics from Prometheus
curl -s "http://prometheus:9090/api/v1/query?query=container_memory_usage_bytes{pod=~\"foxhunt-trading-service.*\"}" | jq
```

### Step 2: Profile Memory Usage

```bash
# Run with memory profiler (Rust: valgrind + massif)
kubectl exec -it foxhunt-trading-service-xxxxx -n foxhunt -- /bin/bash

# Inside container:
valgrind --tool=massif --massif-out-file=/tmp/massif.out ./trading_service

# Analyze massif output
ms_print /tmp/massif.out | head -100
```

---

## Common Causes

### Cause 1: Unbounded Cache

**Symptom**: Memory grows linearly with time

**Diagnosis**:
```rust
// Check for unbounded HashMap/Vec
let cache: HashMap<String, Data> = HashMap::new();  // No size limit!
```

**Resolution**:
```rust
// Use LRU cache with size limit
use lru::LruCache;
let mut cache: LruCache<String, Data> = LruCache::new(1000);
```

### Cause 2: Connection Leaks

**Symptom**: Memory grows with database connections

**Diagnosis**:
```bash
# Check active connections
kubectl exec -n foxhunt foxhunt-postgresql-0 -- \
    psql -U foxhunt -d foxhunt -c "SELECT count(*), state FROM pg_stat_activity GROUP BY state;"
```

**Resolution**:
```rust
// Ensure connections are returned to pool
async fn query_db(pool: &PgPool) -> Result<()> {
    let mut conn = pool.acquire().await?;
    let result = sqlx::query("SELECT * FROM orders").fetch_all(&mut conn).await?;
    drop(conn);  // Explicitly return to pool
    Ok(())
}
```

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**End of Memory Leak Troubleshooting Guide**