Database performance optimization - query optimization, execution plans, and caching strategies

Database Optimization

Database performance optimization is critical for building scalable applications. This section covers techniques to identify and resolve performance bottlenecks.

Why Optimize?

Performance Impact:
┌─────────────────────────────────────────────────────────┐
│ Slow queries → High latency → Poor user experience      │
│ Resource waste → Higher costs → Scalability issues      │
│ Lock contention → Throughput drop → System bottleneck   │
└─────────────────────────────────────────────────────────┘

Optimization benefits:
- Faster response times
- Lower infrastructure costs
- Better scalability
- Improved user experience

Optimization Workflow

┌─────────────────────────────────────────────────────────┐
│ 1. Identify Problem                                     │
│    - Monitor slow queries                               │
│    - Analyze resource usage                             │
│    - Profile application                                │
└──────────────────────┬──────────────────────────────────┘
                       │
┌──────────────────────▼──────────────────────────────────┐
│ 2. Analyze Root Cause                                   │
│    - Examine execution plans                            │
│    - Check index usage                                  │
│    - Review query patterns                              │
└──────────────────────┬──────────────────────────────────┘
                       │
┌──────────────────────▼──────────────────────────────────┐
│ 3. Implement Solution                                   │
│    - Add/modify indexes                                 │
│    - Rewrite queries                                    │
│    - Implement caching                                  │
└──────────────────────┬──────────────────────────────────┘
                       │
┌──────────────────────▼──────────────────────────────────┐
│ 4. Measure Results                                      │
│    - Compare before/after metrics                       │
│    - Validate improvements                              │
│    - Monitor for regressions                            │
└─────────────────────────────────────────────────────────┘

Common Performance Issues

Issue	Symptoms	Solution
Missing indexes	Full table scans, slow WHERE/JOIN	Add appropriate indexes
N+1 queries	Many small queries, high latency	Use JOINs or batch queries
Large result sets	High memory usage, slow transfers	Pagination, projections
Lock contention	Wait times, deadlocks	Optimize transactions, indexing
Outdated statistics	Poor query plans	Update statistics regularly

Monitoring Queries

PostgreSQL Slow Query Log

-- Enable slow query logging
ALTER SYSTEM SET log_min_duration_statement = '1000';  -- 1 second

-- View long-running queries
SELECT pid, now() - pg_stat_activity.query_start AS duration, query
FROM pg_stat_activity
WHERE state != 'idle'
  AND now() - pg_stat_activity.query_start > interval '5 seconds';

-- Top 10 slowest queries (requires pg_stat_statements extension)
SELECT query, calls, mean_exec_time, total_exec_time
FROM pg_stat_statements
ORDER BY mean_exec_time DESC
LIMIT 10;

MySQL Slow Query Log

-- Enable slow query log
SET GLOBAL slow_query_log = 'ON';
SET GLOBAL long_query_time = 1;  -- 1 second

-- View process list
SHOW PROCESSLIST;

-- Query performance schema
SELECT * FROM performance_schema.events_statements_summary_by_digest
ORDER BY SUM_TIMER_WAIT DESC
LIMIT 10;

Topics

Query Optimization - Writing efficient queries, avoiding common pitfalls
Execution Plans - Understanding and analyzing query execution plans
Caching - Database caching, application-level caching, cache invalidation

Database Optimization

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