language agnostic - What is eager loading?

Question

What is eager loading? I code in PHP/JS but a more generalised answer will be just fine.

I saw a lot of questions regarding Java & Ruby, but i don't know any of these languages, and I find it hard to read code. I don't know whats supposed to do in the first place

Answer 1

There are three levels:

1. Eager loading: you do everything when asked. Classic example is when you multiply two matrices. You do all the calculations. That's eager loading;
2. Lazy loading: you only do a calculation when required. In the previous example, you don't do any calculations until you access an element of the result matrix; and
3. Over-eager loading: this is where you try and anticipate what the user will ask for and preload it.

I hope that makes sense in the context you're seeing it.

Let me give you a "Webby" example.

Imagine a page with rollover images like for menu items or navigation. There are three ways the image loading could work on this page:

1. Load every single image required before you render the page (eager);
2. Load only the displayed images on page load and load the others if/when they are required (lazy); and
3. Load only the displayed images on page load. After the page has loaded preload the other images in the background in case you need them (over-eager).

Make sense?