🟢 Basic Level
1. What is PHP performance optimization?
👉 Improving execution speed, reducing memory usage, and minimizing server load.
2. What is caching in PHP?
👉 Storing frequently used data to avoid repeated computation or database queries.
3. Types of caching in PHP?
- Output caching
- File caching
- Opcode caching (OPcache)
- Memory caching (Redis, Memcached)
4. What is OPcache?
👉 A bytecode cache that stores compiled PHP scripts in memory to avoid recompilation.
5. Difference between require, include, require_once?
👉 require_once prevents multiple inclusions → improves performance & avoids errors.
6. What is the use of isset() vs empty()?
isset()→ checks variable exists (faster)empty()→ checks if value is empty
🟡 Intermediate Level
7. How can you reduce database load in PHP?
- Use caching (Redis/Memcached)
- Optimize queries (JOIN instead of loops)
- Use indexing
- Limit results
8. Why is count() inside loops bad?
👉 It recalculates each iteration → increases execution time.
9. How does OPcache improve performance?
👉 Stores compiled bytecode → avoids parsing & compilation on every request.
10. What are persistent database connections?
👉 Connections reused across requests → reduces connection overhead.
11. Difference between echo and print?
echois fasterprintreturns value (slightly slower)
12. What is lazy loading?
👉 Loading data only when needed instead of loading everything at once.
13. How to optimize large PHP applications?
- Modular code
- Use caching layers
- Queue background jobs
- Optimize DB queries
🔴 Advanced Level
14. How does PHP handle memory management?
👉 Uses reference counting + garbage collection for unused objects.
15. What is the role of a CDN in PHP performance?
👉 Serves static files faster from global servers → reduces server load.
16. What is opcode caching vs data caching?
- Opcode caching → compiled PHP code
- Data caching → application data (Redis, Memcached)
17. How do you profile a PHP application?
Tools:
- Xdebug
- Blackfire
- New Relic
18. What is N+1 query problem?
👉 Running queries inside loops → causes multiple DB hits.
19. How can you optimize API response time?
- Cache responses
- Use pagination
- Compress output (Gzip)
- Reduce payload size
20. What are PHP-FPM and its benefits?
👉 FastCGI Process Manager
- Handles multiple requests efficiently
- Better resource management
21. What is output buffering?
👉 Stores output in memory before sending → improves performance & control.
22. How do you handle high traffic in PHP apps?
- Load balancing
- Horizontal scaling
- Caching (Redis/CDN)
- Queue systems (RabbitMQ)
23. What is autoloading and its performance impact?
👉 Loads classes automatically → reduces unnecessary file includes.
24. Explain session performance optimization.
- Store sessions in Redis
- Avoid large session data
- Use session_write_close()
25. How to optimize file handling in PHP?
- Read files in chunks
- Avoid loading large files into memory
🧠 Scenario-Based Questions (Important)
26. Website is slow. What will you check first?
👉 Server load, DB queries, caching, network latency
27. DB queries are slow. What will you do?
👉 Add indexes, optimize queries, reduce joins, caching
28. High traffic crash issue. Solution?
👉 Load balancer + caching + queue system
29. API response taking 5 seconds. Fix?
👉 Profile code → optimize DB → cache → reduce payload
30. Memory limit exceeded error?
👉 Optimize loops, unset variables, increase memory if needed
🔥 Pro Interview Tips
- Always mention Redis + OPcache + Indexing
- Use words like:
- “Scalability”
- “Bottleneck”
- “Profiling”
- “Optimization strategy”
🎯 Bonus Rapid Fire
- Fastest output method? →
echo - Best cache? → Redis
- Improve PHP speed instantly? → Enable OPcache
- Reduce DB calls? → Use caching
