Three myths about database indexing

We end up explaining this on discovery calls often enough that it deserved writing down. A few things about database indexing that get repeated more often than they get checked.

Real-world numbers from actual visitors matter more than a score produced on a fast laptop. It rarely shows up as a line item, which is exactly why it slips.

“It only matters for big sites”

The right index turns seconds into milliseconds. That sounds obvious written down. It is still the thing most often skipped. The teams that stay on top of it are the ones who put it on a calendar rather than a wish list.

“We can deal with it after launch”

Sometimes true, usually expensive. Where this goes wrong is almost never a lack of knowledge.

“Our platform handles it”

Look at the query plan instead of guessing. None of that requires a large budget, only a decision and someone to own it. It rarely shows up as a line item, which is exactly why it slips.

In practice

Performance work is mostly subtraction, which makes it unpopular and effective. Three things worth confirming about database indexing before you move on:

• Someone can say what the current setup is without going to look
• Every index also slows writes, so be deliberate — and you know whether that is true here
• There is a way to tell whether the last change to this helped

The point is not perfection, it is knowing which of these you have consciously chosen to skip.