Why “Let’s Just Add a Cache” Is a Red Flag

When a system is slow, one of the first suggestions that comes up is: “let’s add a cache.”

Sometimes that really helps. But often - it’s a warning sign.

Because a cache is a bandage. Not a cure.

What a Cache Doesn’t Solve

A cache speeds up access to data that was already here before. It doesn’t solve:

• Slow logic
• Unnecessary dependencies
• Uncontrolled load
• Or a problematic flow in the system

It just hides them - for a while.

When a Cache Is the Right Tool

There are situations where a cache is the right tool:

• Data that’s read a lot and doesn’t change often
• An expensive computation whose result is stable
• A clear, well-understood read load

In these cases, a cache saves real work. It improves performance without changing behavior.

But these aren’t the problematic cases.

When a Cache Is a Red Flag

The red flag appears when a cache is proposed as a general response:

• “It’s slow? Let’s add a cache”
• “There’s load? Let’s put a cache in front”
• “Not clear why it’s stuck? A cache will help”

Here, the cache no longer solves a problem - it blurs it.

Hidden Dependency on Behavior

The big danger is that a cache creates a hidden dependency on behavior.

After adding a cache:

• The system “works” as long as it’s warm
• The real behavior only shows up on a cache miss
• And incidents happen precisely at unusual moments

Suddenly:

• A small restart feels like a disaster
• A configuration change breaks performance
• And a momentary load spike triggers unpredictable behavior

Not because the system is bad - but because it learned to lean on the cache.

The Hit to Stability

An uncontrolled cache also hurts stability.

Because a cache:

• Adds state
• Adds timing
• And adds the complexity of eviction, consistency, and validity

And when it’s unclear:

• Who depends on the cache
• What happens when it empties out
• And how the system behaves without it

Performance might improve, but the ability to understand and predict behavior - suffers.

The Analogy: A Painkiller

A painkiller can bring relief - but it doesn’t cure the problem.

If every pain is solved only with a painkiller, you stop asking why it hurts.

A cache works exactly the same way.

Summary

A cache is an important tool, but it has to arrive after understanding, not instead of it.

A mature system doesn’t ask “where should we add a cache?” but rather “what’s actually slowing us down - and does a cache address the cause, or just cover it up?”

Because a bandage can bring relief for a moment. But only a cure brings a system back to real health.