Redis  

Redis Cache Patterns Explained: Cache-Aside vs Read-Through vs Write-Through vs Write-Behind

Why Cache Patterns Matter More Than Redis Commands

Most Redis-related issues in production systems have very little to do with Redis itself. They originate from choosing the wrong caching pattern for the application’s architecture.

Redis is fast. Redis is reliable. However, Redis will faithfully amplify poor design decisions.

A cache pattern defines:

  • Who controls the data flow

  • Who owns data consistency

  • Who absorbs the impact when failures occur

When these decisions are unclear, systems suffer from:

  • Stale data

  • Double writes

  • Cache storms

  • Silent data corruption

Choosing the right cache pattern is an architectural decision, not a Redis configuration detail.

Pattern 1: Cache-Aside (Lazy Loading)

Cache-aside is the default pattern that should be used unless there is a strong and well-justified reason to choose otherwise.

How cache-aside works:

  • The application checks Redis first

  • If data exists, it is returned immediately

  • If data does not exist:

    • Data is read from the database

    • The result is stored in Redis with a TTL

    • The data is returned to the caller

Redis is never the source of truth. The database always remains authoritative.

Why Cache-Aside Works Well in Production

Cache-aside is widely adopted because it provides:

  • A simple and intuitive mental model

  • Easy failure handling

  • Safe behavior during Redis outages

  • Loose coupling between cache and database

If Redis becomes unavailable, the application continues to function, temporarily falling back to the database. Only performance is affected, not correctness.

Cache-Aside Example in C#

public async Task<Product> GetProductAsync(int id)
{
    string key = $"product:{id}";
    var cached = await _cache.StringGetAsync(key);

    if (cached.HasValue)
    {
        return JsonSerializer.Deserialize<Product>(cached);
    }

    var product = await _repository.GetByIdAsync(id);
    if (product == null) return null;

    await _cache.StringSetAsync(
        key,
        JsonSerializer.Serialize(product),
        TimeSpan.FromMinutes(15)
    );

    return product;
}

Tradeoffs of Cache-Aside

Cache-aside comes with acceptable tradeoffs:

  • Initial cache miss penalty on first request

  • Potentially stale data until TTL expires

  • Explicit invalidation required on writes

For most web, enterprise, and SaaS applications, these tradeoffs are reasonable.

Pattern 2: Read-Through Cache

In a read-through cache, the application never accesses the database directly. Instead:

  • The application requests data from Redis

  • Redis loads the data from the database if it is missing

  • Redis returns the data to the application

Redis becomes an active participant in the data access path.

Why Read-Through Looks Attractive

Teams are drawn to read-through caching because it offers:

  • Cleaner application code

  • Centralized caching logic

  • Consistent data access behavior

Operational Risks of Read-Through

Redis does not natively support read-through caching. Implementing it requires:

  • Custom middleware

  • Sidecar services

  • Tight coupling between cache and database

This makes Redis availability business critical. If Redis fails, the application cannot read data even when the database is healthy.

For this reason, read-through caching is uncommon outside tightly controlled enterprise environments or managed platforms.

When Read-Through Is Appropriate

Read-through caching can work when:

  • The environment is tightly controlled

  • The system is read-heavy

  • Redis availability is guaranteed through strong operational practices

In most cases, cache-aside remains the safer choice.

Pattern 3: Write-Through Cache

With write-through caching:

  • Every write goes to Redis first

  • Redis synchronously writes data to the database

  • Reads always hit Redis

Benefits of Write-Through

Write-through ensures:

  • Fresh cache entries

  • No stale reads

  • Simple and predictable read paths

Performance and Reliability Costs

The main drawback of write-through caching is latency. Each write operation must wait for:

  • Redis

  • The database

If either component slows down, write throughput degrades significantly.

Real-world challenges include:

  • Increased write latency

  • Redis becoming a bottleneck

  • Complex rollback handling during partial failures

Write-through caching is best suited for systems where consistency is more important than raw performance and write volume is relatively low.

Pattern 4: Write-Behind (Write-Back) Cache

Write-behind caching is both powerful and risky.

  • Writes are stored in Redis first

  • Database updates occur asynchronously later

Why Teams Use Write-Behind

Write-behind provides:

  • Extremely fast write performance

  • High throughput

  • Suitability for analytics and telemetry workloads

The Risk of Data Loss

If Redis fails before data is persisted to the database, the data is permanently lost. There is no automatic recovery.

When Write-Behind Is Acceptable

Write-behind caching is suitable for:

  • Eventual consistency systems

  • Analytics pipelines

  • Logging systems

  • Metrics collection

  • Click tracking

It should never be used for:

  • Payments

  • Orders

  • User profile data

  • Financial or compliance records

Choosing the Right Cache Pattern

A practical architectural guide:

  • Cache-aside: best default for most applications

  • Read-through: use only with strong operational guarantees

  • Write-through: consistency first, performance second

  • Write-behind: performance first, data loss acceptable

A Production Rule Worth Remembering

Redis is not magic, and caching is never free.

Always decide upfront:

  • Who owns the source of truth

  • Who owns failure handling

  • Who absorbs latency costs

When these decisions are explicit, Redis becomes a powerful optimization layer rather than a source of production incidents.

Membership not found