[Python-Dev] Python startup time

[Steven D'Aprano]

On Wed, Jul 19, 2017 at 04:11:24PM -0700, Chris Barker wrote:
> As long as we are talking anecdotes:
> 
> If it could save a person’s life, could you find a way to save ten seconds
> off the boot time? If there were five million people using the Mac, and it
> took ten seconds extra to turn it on every day, that added up to three
> hundred million or so hours per year people would save, which was the
> equivalent of at least one hundred lifetimes saved per year.
> 
> Steve Jobs.

And about a fifth of the time they spent standing in lines waiting to 
buy the latest unnecessary iGadget... 

But seriously, that calculation is completely bogus. Not only is Steve 
Job's arithmetic *completely* wrong, but the whole premise is nonsense.

Do the maths yourself: ten seconds per day is 3650 seconds in a year, 
which is slightly over an hour (3600 seconds). Multiply by five million 
users, that's about five million hours, not 300 million. So Jobs 
exaggerates the time saved by a factor of sixty.

(Or maybe Jobs was warning that Macs crash sixty times a day...)

But the premise is wrong too. Those hypothetical people don't turn their 
Macs on in sequence, each person turning their computer on only after 
the previous person's Mac had finished booting. They effectively boot 
them up in parallel but offset, spread out over a 24 hour period, so 
about 3472 people booting up at the same time each minute of the day. 
Time savings for parallel processes don't add in the way Jobs adds them, 
if we treat this as 1440 parallel processes (one per minute of the day) 
we save 1440 hours a year.

But really, the only meaningful calculation is the each person saves 10 
seconds per day. We can't even meaningfully say they save one hour a 
year: it doesn't come nicely packaged up for you all at once, so you can 
actually do something useful with it, nor can you save those ten seconds 
from one day to the next. You only get one shot at using them. What can 
you do with ten seconds per day? By the time you decide what to do with 
the extra time, it's already gone.

There are good reasons for speeding up boot time, but this sort of 
calculation is not one of them. I think it is in particularly bad taste 
to exaggerate the significance of it by putting it in terms of saving 
lives. You want to save real lives? How about fixing the conditions in 
the sweatshops that make Apple phones? And installing suicide nets 
around the building doesn't count.



-- 
Steve