How do you optimize PHP performance (OPcache, JIT)?

Question

Accepted Answer

PHP performance optimization spans **OPcache** (caching compiled code — the single biggest win), the **JIT** compiler (PHP 8), efficient code, caching data, and database optimization. Modern PHP 8.x is dramatically faster than older versions, and proper configuration matters.

## OPcache — the essential optimization

```text
Without OPcache: PHP RE-COMPILES every .php file to bytecode on EVERY request (slow!).
With OPcache: compiled bytecode is CACHED in memory → subsequent requests skip
  compilation entirely → often 2-3x faster. ALWAYS enable it in production.
```

```ini
; php.ini — enable and tune OPcache
opcache.enable=1
opcache.memory_consumption=256
opcache.max_accelerated_files=20000
opcache.validate_timestamps=0    ; production: don't check files for changes (fastest)
```

**OPcache** caches the compiled bytecode of your PHP files in memory so PHP doesn't recompile on every request — typically a 2-3x speedup, and it's the most important production optimization (often just enabling it).

## JIT (Just-In-Time compilation, PHP 8)

```ini
opcache.jit_buffer_size=128M
opcache.jit=tracing
```

```text
The JIT compiles hot code to native machine code at runtime.
✓ Big gains for CPU-INTENSIVE work (math, image processing, computation)
✗ Little benefit for typical I/O-bound web apps (DB/network are the bottleneck, not CPU)
→ Helps specific workloads; not a magic speedup for regular web requests.
```

The JIT helps CPU-bound workloads but offers little for typical I/O-bound web apps (where the database/network dominates) — so set realistic expectations.

## Application-level optimizations

```text
✓ The DATABASE is usually the real bottleneck — fix N+1 queries, add indexes, paginate
✓ Cache expensive results (Redis/Memcached); cache rendered output where possible
✓ Optimize Composer autoloading for production: composer dump-autoload -o
✓ Use efficient algorithms/data structures; avoid heavy work in loops
✓ Offload slow tasks to queues (don't block the request)
✓ Use a recent PHP version — each 8.x release brings real performance gains
```

## Measure first

```text
Use profilers (Xdebug, Blackfire, Tideways) to find the ACTUAL bottleneck.
For most web apps it's the database or external calls, NOT PHP code itself.
```

## Why it matters

PHP performance optimization is valuable senior-level knowledge, and understanding the key levers — especially the discipline of measuring first — is important for building fast, scalable applications.

The single most impactful optimization is **OPcache**: because PHP would otherwise recompile every file on every request, enabling OPcache (which caches compiled bytecode in memory) typically delivers a 2-3x speedup and is essential, non-negotiable production configuration that's often overlooked.

Understanding the **JIT** compiler (PHP 8) is important for setting realistic expectations — it helps CPU-intensive workloads but offers little for typical I/O-bound web apps, so it's not a universal speedup.

Beyond PHP-level tuning, recognizing that the **database is usually the real bottleneck** (so fixing N+1 queries, adding indexes, and pagination deliver the biggest real-world gains), along with data caching (Redis), optimized autoloading, and offloading slow work to queues, covers the practical optimization toolkit.

The overarching discipline — **profiling to find the actual bottleneck** (usually the database or external calls, not PHP code) rather than guessing — is what makes optimization effective.

Also worth knowing: modern PHP 8.x is dramatically faster than older versions, so simply staying current helps.

Understanding OPcache (the essential win), the JIT's realistic role, database-focused optimization, and measurement-driven tuning is important knowledge for keeping PHP applications fast under real load — a frequent, practically-significant concern for production systems.