benchmark of shift vs pop with node.js

shift_vs_pop.js

'use strict'

const size = 130000

let arr1 = new Array(size)
let arr2 = new Array(size)

for (let i = 0; i < size; i++) {
	arr1[i] = i + ''
	arr2[i] = i + ''
}

console.time('pop')
for (let i = 0; i < size; i++) {
	let r = arr1.pop()
	if (r > size) console.log(1)
}
console.timeEnd('pop')

console.time('shift')
for (let i = 0; i < size; i++) {
	let r = arr2.shift()
	if (r > size) console.log(1)
}
console.timeEnd('shift')

Weirdly enough, on my machine, when size === 128990 performance are the same:

pop: 32.506ms
shift: 31.557ms

but when size === 128991, performance of shift() dramatically degrades:

pop: 36.992ms
shift: 10631.207ms

Tested this also on an amazon linux machine, got the same behaviour. Leading me to believe that it's part of some underlying optimization, rather than a direct effect of hardware.

Reversing the array seems to work:

'use strict'

const size = 128991

let arr1 = new Array(size)
let arr2 = new Array(size)
let arr3 = new Array(size)

for (let i = 0; i < size; i++) {
    arr1[i] = i + ''
    arr2[i] = i + ''
    arr3[i] = i + ''
}

console.time('pop')
for (let i = 0; i < size; i++) {
    let r = arr1.pop()
    if (r > size) console.log(1)
}
console.timeEnd('pop')

console.time('shift')
for (let i = 0; i < size; i++) {
    let r = arr2.shift()
    if (r > size) console.log(1)
}
console.timeEnd('shift')

console.time('reverse')
arr3.reverse()
for (let i = 0; i < size; i++) {
    let r = arr3.pop()
    if (r > size) console.log(1)
}
console.timeEnd('reverse')

results in:

pop: 35.088ms
shift: 10421.718ms
reverse: 37.479ms