What is caching?

Question

I\'m constantly hearing about person y had performance issue x which they solved through caching.

Or, how doing x,y,z in your programs code can hurt your caching abil

Answer 1

Caching does not necessarily only apply to 'oft retrieved' values but to anything you can save time on by reducing the number of times you recompute it. A simple example that comes to mind is calculating the fibonacci sequence. The simplest recursive implementation looks like this (in psuedo-code):

function f(n)
    if n < 2 then
        return n;
    return f(n - 1) + f(n - 2)

This can be improved with caching to prevent recalculating already known values:

fib_cache = {}

function f(n)
    if n < 2 then
        return n;
    if fib_cache.contains(n) then
        return fib_cache[n]
    fib_cache[n] = f(n - 1) + f(n - 2)
    return fib_cache[n]