How to debug and log PHP OPcache Issues

PHP OPcache can sometimes cause unexpected behavior in your applications. When debugging OPcache-related issues, you need systematic approaches to identify and resolve problems effectively.

Temporarily Disable OPcache

The first step in debugging OPcache issues is to temporarily disable it and see if the problem persists ?

<?php
    // Disable OPcache for this script
    ini_set('opcache.enable', 0);
    
    echo "OPcache disabled for debugging<br>";
    echo "OPcache enabled: " . (ini_get('opcache.enable') ? 'Yes' : 'No');
?>

OPcache disabled for debugging
OPcache enabled: No

This approach helps determine if OPcache is the root cause without disabling other extensions.

Enable Detailed Error Reporting

When OPcache is enabled, you need comprehensive error reporting to identify specific issues ?

<?php
    // Enable all error reporting
    ini_set('display_errors', 1);
    error_reporting(E_ALL);
    
    // Also log errors
    ini_set('log_errors', 1);
    ini_set('error_log', '/tmp/php_errors.log');
    
    echo "Error reporting enabled<br>";
    echo "Error level: " . error_reporting();
?>

Error reporting enabled
Error level: 32767

Check OPcache Status

Monitor OPcache statistics to understand its behavior and identify potential issues ?

<?php
    if (function_exists('opcache_get_status')) {
        $status = opcache_get_status();
        
        echo "OPcache enabled: " . ($status['opcache_enabled'] ? 'Yes' : 'No') . "<br>";
        echo "Cache full: " . ($status['cache_full'] ? 'Yes' : 'No') . "<br>";
        echo "Hit rate: " . round($status['opcache_statistics']['opcache_hit_rate'], 2) . "%<br>";
        echo "Used memory: " . round($status['memory_usage']['used_memory'] / 1024 / 1024, 2) . " MB<br>";
    } else {
        echo "OPcache not available<br>";
    }
?>

OPcache enabled: Yes
Cache full: No
Hit rate: 95.67%
Used memory: 45.23 MB

Common Debugging Techniques

Clear OPcache programmatically: Use opcache_reset() to clear the cache when testing changes.

Use Xdebug: For complex debugging scenarios, Xdebug provides remote debugging capabilities that work alongside OPcache.

Check file timestamps: Ensure opcache.validate_timestamps is enabled during development to detect file changes.

Conclusion

Start by disabling OPcache to isolate the issue, then use detailed error reporting and status monitoring. For complex cases, combine these techniques with tools like Xdebug for comprehensive debugging.