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intermediate Phase 68 · Cache System

Redis in Magento 2 — Cache Backend and Session Storage

Configuring Redis in Magento 2: cache backend, session storage, full page cache, and Redis performance optimization

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Redis Cache Backend

env.php Configuration

// app/etc/env.php
return [
    'cache' => [
        'frontend' => [
            'default' => [
                'backend' => 'Magento\Framework\Cache\Backend\Redis',
                'backend_options' => [
                    'server' => '127.0.0.1',
                    'port' => '6379',
                    'database' => '0',
                    'compress_data' => '1'
                ]
            ],
            'page_cache' => [
                'backend' => 'Magento\Framework\Cache\Backend\Redis',
                'backend_options' => [
                    'server' => '127.0.0.1',
                    'port' => '6379',
                    'database' => '1',
                    'compress_data' => '0'
                ]
            ]
        ]
    ]
];

Redis Databases

Database Purpose
0 Default cache
1 Full page cache
2 Session storage
3-15 Custom use

Setup Command

php bin/magento setup:config:set \
    --cache-backend=redis \
    --cache-backend-redis-server=127.0.0.1 \
    --cache-backend-redis-port=6379 \
    --cache-backend-redis-db=0

Redis Session Storage

Session Configuration

// app/etc/env.php
return [
    'session' => [
        'save' => 'redis',
        'redis' => [
            'host' => '127.0.0.1',
            'port' => '6379',
            'database' => '2',
            'password' => '',
            'timeout' => '2.5',
            'persistent_identifier' => '',
            'log_level' => '3',
            'max_concurrency' => '20',
            'breaker' => [
                'timeout' => '15',
                'sleep' => '1'
            ]
        ]
    ]
];

Setup Command

php bin/magento setup:config:set \
    --session-save=redis \
    --session-save-redis-host=127.0.0.1 \
    --session-save-redis-port=6379 \
    --session-save-redis-db=2

Session Performance

// Redis session vs file session
// File: ~5-10ms per read/write
// Redis: ~0.5-1ms per read/write

// For 100 concurrent users:
// File: 500-1000ms total
// Redis: 50-100ms total

Redis Full Page Cache

FPC Configuration

// app/etc/env.php
return [
    'cache' => [
        'frontend' => [
            'page_cache' => [
                'backend' => 'Magento\Framework\Cache\Backend\Redis',
                'backend_options' => [
                    'server' => '127.0.0.1',
                    'port' => '6379',
                    'database' => '1',
                    'compress_data' => '0',
                    'compression_lib' => ''
                ]
            ]
        ]
    ]
];

FPC with Redis

// Enable FPC
php bin/magento config:set catalog/frontend/flat_catalog 1

// Check FPC hit rate
php bin/magento cache:status | grep fpc

Redis Memory Management

# Check Redis memory usage
redis-cli info memory

# Set memory limit
redis-cli config set maxmemory 2gb

# Set eviction policy
redis-cli config set maxmemory-policy allkeys-lru

Redis Performance Optimization

Redis Configuration

# /etc/redis/redis.conf
maxmemory 4gb
maxmemory-policy allkeys-lru
save 900 1
save 300 10
save 60 10000
appendonly yes
appendfsync everysec

Monitoring

# Check Redis status
redis-cli info

# Monitor commands
redis-cli monitor

# Check slow log
redis-cli slowlog get 10

# Check connected clients
redis-cli client list

Connection Pooling

// env.php - persistent connections
'cache' => [
    'frontend' => [
        'default' => [
            'backend_options' => [
                'server' => '127.0.0.1',
                'port' => '6379',
                'database' => '0',
                'compress_data' => '1',
                'compression_lib' => 'gzip'
            ]
        ]
    ]
]

Performance Metrics

Metric File Backend Redis Backend
Read time 5-10ms 0.5-1ms
Write time 5-10ms 0.5-1ms
Memory Disk-based RAM-based
Concurrency File locks Lock-free
Scalability Limited Horizontal

Practice Problems

0 / 1 solved
Redis Migration

Migrate a Magento store from file-based cache to Redis. Plan the migration steps.

Quiz

1. What Redis database is used for default cache?

Question 1 options

2. What is the recommended eviction policy for Redis with Magento?

Question 2 options

3. How much faster is Redis vs file-based cache?

Question 3 options

4. What env.php key configures Redis sessions?

Question 4 options

Flashcards

Question

What Redis database is used for sessions?

Click to reveal answer

Answer

Database 2

Question

How to enable Redis cache backend?

Click to reveal answer

Answer

Set cache.frontend.default.backend to Magento\Framework\Cache\Backend\Redis

Question

What is the recommended Redis eviction policy?

Click to reveal answer

Answer

allkeys-lru for Magento cache

Question

How to check Redis memory usage?

Click to reveal answer

Answer

redis-cli info memory

Question

What Redis feature benefits sessions most?

Click to reveal answer

Answer

In-memory storage with sub-millisecond latency

Revision Notes

Key Takeaways

  • 1. Redis databases: 0=default cache, 1=FPC, 2=sessions
  • 2. Configure in env.php under cache.frontend and session keys
  • 3. Redis provides 5-10x faster cache operations than file backend
  • 4. Set maxmemory and allkeys-lru eviction policy
  • 5. Monitor with redis-cli info, monitor, and slowlog commands
  • 6. Use compress_data for default cache but not FPC

Interview Tips

  • • Explain Redis database assignment for Magento
  • • Describe the performance benefits of Redis over file cache
  • • Discuss Redis memory management and eviction
  • • Know the env.php configuration structure

Cheat Sheet

Redis Cheat Sheet

Databases:

  • 0: default cache
  • 1: FPC
  • 2: sessions

env.php:

'cache' => ['frontend' => ['default' => [
    'backend' => '...Redis',
    'backend_options' => ['server' => '127.0.0.1', 'port' => '6379', 'database' => '0']
]]]

Setup:
php bin/magento setup:config:set --cache-backend=redis

Monitor:
redis-cli info
redis-cli monitor
redis-cli slowlog get 10

Performance: 0.5-1ms vs 5-10ms (file)