Redis Shared Database Analyzer

Analyzer ID	Category	Severity	Time To Fix
redis-shared-database	✅ Reliability	High	5 minutes

What This Checks

• Detects when Redis cache shares the same database number with queue connections (running cache:clear deletes pending jobs)
• Detects when Redis cache shares the same database number with session storage (running cache:clear logs out all users)
• Detects when Redis cache shares the same database number with Laravel Horizon (running cache:clear clears Horizon metrics and pending jobs)
• Builds connection identifiers from host:port:database to detect collisions even across named connections
• Resolves connections defined by a url (e.g. tls://user:pass@host:6380?database=1) to their real host, port, and database — matching Laravel's own connector, where url takes precedence over the discrete host/port/database keys
• Supports Redis cluster configurations by comparing cluster connection names
• Does not treat key prefixes as isolation: cache:clear calls Redis FLUSHDB, which deletes every key in the database regardless of prefix (broadcasting is not checked — Redis pub/sub is not persisted as keys and is unaffected by FLUSHDB)

Why It Matters

• Accidental data loss: Running php artisan cache:clear is a routine maintenance operation, but when cache shares a database with queues or sessions it silently deletes all queued jobs and user sessions
• Cache eviction side effects: If an eviction policy like allkeys-lru is active, Redis may evict queue jobs or session data to make room for cache entries
• Debugging difficulty: When cache, queue, and session keys are mixed in the same database, diagnosing issues with redis-cli KEYS * becomes a guessing game
• Deployment failures: Automated deployment scripts that clear cache between releases can cause production outages by destroying active sessions and pending background jobs
• Horizon data loss: Clearing the shared database removes Horizon's job metrics, failed job tracking, and supervision state

How to Fix

Isolate the cache so it resolves to a different physical Redis database than queues, sessions, and Horizon. Key prefixes do not count — cache:clear calls FLUSHDB, which wipes the entire database regardless of prefix.

Quick Fix (2 minutes)

On a self-hosted Redis that supports multiple databases (Forge, Docker), give the cache its own database number:

# .env
REDIS_CACHE_DB=1

This does not work on managed single-database Redis (Laravel Valkey, Upstash, ElastiCache cluster mode), where SELECT 1 collapses to database 0 — and that is exactly the environment that produces this finding, since the default Laravel skeleton isolates cache purely by REDIS_CACHE_DB. The one-line escape hatch that works anywhere is to take the cache off Redis entirely:

# .env
CACHE_STORE=database

For a Redis-backed cache on managed/single-database Redis, use the Proper Fix below.

Proper Fix (5 minutes)

Give the cache its own Redis instance so it is isolated regardless of multi-database support. This is the only option that works on managed single-database Redis, and cache:clear then only flushes the dedicated cache instance.

1: Point the cache at a separate instance via environment

# .env
REDIS_URL=tls://default:password@redis-data.example:6379        # queues, sessions, Horizon
REDIS_CACHE_URL=tls://default:password@redis-cache.example:6379 # cache only

2: Configure the connections

// config/database.php
'redis' => [
    'client' => env('REDIS_CLIENT', 'phpredis'),

    // Persistent data: queues, sessions, Horizon
    'default' => [
        'url' => env('REDIS_URL'),
        'host' => env('REDIS_HOST', '127.0.0.1'),
        'port' => env('REDIS_PORT', 6379),
        'database' => env('REDIS_DB', 0),
    ],

    // Dedicated cache instance on a different server
    'cache' => [
        'url' => env('REDIS_CACHE_URL'),
        'host' => env('REDIS_CACHE_HOST', '127.0.0.1'),
        'port' => env('REDIS_CACHE_PORT', 6379),
        'database' => env('REDIS_CACHE_DB', 0),
    ],
],

// config/cache.php
'stores' => [
    'redis' => [
        'driver' => 'redis',
        'connection' => 'cache',  // dedicated cache instance
    ],
],

When url is set it takes precedence over the discrete host/port/database keys, matching Laravel's connector — so the cache connection is compared by the real server in the URL.

3: Multi-database alternative (self-hosted only)

When the Redis server supports multiple databases, a dedicated cache instance is not required — give each service its own database number instead:

# .env
REDIS_DB=0
REDIS_CACHE_DB=1
REDIS_QUEUE_DB=2
REDIS_SESSION_DB=3
REDIS_HORIZON_DB=4

// config/database.php
'redis' => [
    'client' => env('REDIS_CLIENT', 'phpredis'),

    'default' => [
        'host' => env('REDIS_HOST', '127.0.0.1'),
        'port' => env('REDIS_PORT', 6379),
        'database' => env('REDIS_DB', 0),
    ],

    'cache' => [
        'host' => env('REDIS_HOST', '127.0.0.1'),
        'port' => env('REDIS_PORT', 6379),
        'database' => env('REDIS_CACHE_DB', 1),
    ],

    'queue' => [
        'host' => env('REDIS_HOST', '127.0.0.1'),
        'port' => env('REDIS_PORT', 6379),
        'database' => env('REDIS_QUEUE_DB', 2),
    ],

    'session' => [
        'host' => env('REDIS_HOST', '127.0.0.1'),
        'port' => env('REDIS_PORT', 6379),
        'database' => env('REDIS_SESSION_DB', 3),
    ],

    'horizon' => [
        'host' => env('REDIS_HOST', '127.0.0.1'),
        'port' => env('REDIS_PORT', 6379),
        'database' => env('REDIS_HORIZON_DB', 4),
    ],
],

Then point each service at its connection (config/cache.php → cache, config/queue.php → queue, config/session.php → session, config/horizon.php 'use' => 'horizon').

4: Verify Isolation

# Cache and persistent data should report from different servers/databases
redis-cli -u "$REDIS_CACHE_URL" DBSIZE
redis-cli -u "$REDIS_URL" DBSIZE

# Clearing cache must leave queues and sessions untouched
php artisan cache:clear

References

• Laravel Redis Configuration
• Laravel Cache Configuration
• Laravel Queue Configuration
• Laravel Session Configuration
• Laravel Horizon Configuration
• Redis SELECT Command

Related Analyzers

• Redis Eviction Policy Analyzer - Validates Redis eviction policy is appropriate for your workload
• Cache Prefix Configuration Analyzer - Ensures shared cache backends use unique prefixes
• Cache Status Analyzer - Validates cache connectivity and functionality
• Queue Timeout Configuration Analyzer - Ensures queue timeout and retry_after values are properly configured