3 ms·

efficiency -> scalability, in the sense that serving the request faster will free the server to serve another request. My point is that for nearly all apps, ex

by nir 17y ago

efficiency -> scalability, in the sense that serving the request faster will free the server to serve another request. My point is that for nearly all apps, executing PHP is very small part of the total request handling time, so even a significant improvement will have little overall effect. I bet many people excited by HipHop could get a much bigger performance gain by adding some simple caching)

rythie 17y ago
Not really, that type of efficiency is not predictable. From Wikipedia: "scalability is a desirable property of a system, a network, or a process, which indicates its ability to either handle growing amounts of work in a graceful manner or to be readily enlarged. For example, it can refer to the capability of a system to increase total throughput under an increased load when resources (typically hardware) are added."
- nir 17y ago
  I realize we're nitpicking, but I don't really get it: Why isn't it predictable (in the sense that any execution time for an HTTP request ever is)? You run http_load for x seconds and see how many requests got served, then make change y and do it again. Obviously there are other variables but it's possible to get a fair idea.
  - rythie 17y ago
    Because as you described you have to try it to find out how much it will save you, by which point you could probably just roll it out already. Say you have 10 servers now and you expect business to grow by 10x in next year, so you put 6 months of dev. time into implementing caching. Then you get 10x the traffic in a month and you get V.C. investment as a result. You then have a problem, people are getting a bad experience and the development won't be done for another 5 months. Your CEO buys a rack full of servers, but you can't do anything with them because you don't have a scalable system. Alternatively you could find out after 6 months that you can't make that 10x performance jump after all. Twitter had this problem a while back, essentially their DB server got overloaded but it was already a 8 CPU, 64GB machine and despite having lots of money they couldn't quickly solve the problem, because you couldn't really get a bigger system. Facebook knows how to scale, they want to cut costs where they can to become (more) profitable.
- deleted 17y ago
  [deleted]
lallysingh 17y ago
It's more like scalability is the derivative of efficiency, for N_1 and N_2 user counts, scalability = (efficiency(N_2) - efficiency(N_1))/(N_2 - N_1)

by nir 17y ago

rythie 17y ago

Not really, that type of efficiency is not predictable. From Wikipedia: "scalability is a desirable property of a system, a network, or a process, which indicates its ability to either handle growing amounts of work in a graceful manner or to be readily enlarged. For example, it can refer to the capability of a system to increase total throughput under an increased load when resources (typically hardware) are added."

nir 17y ago
I realize we're nitpicking, but I don't really get it: Why isn't it predictable (in the sense that any execution time for an HTTP request ever is)? You run http_load for x seconds and see how many requests got served, then make change y and do it again. Obviously there are other variables but it's possible to get a fair idea.
- rythie 17y ago
  Because as you described you have to try it to find out how much it will save you, by which point you could probably just roll it out already. Say you have 10 servers now and you expect business to grow by 10x in next year, so you put 6 months of dev. time into implementing caching. Then you get 10x the traffic in a month and you get V.C. investment as a result. You then have a problem, people are getting a bad experience and the development won't be done for another 5 months. Your CEO buys a rack full of servers, but you can't do anything with them because you don't have a scalable system. Alternatively you could find out after 6 months that you can't make that 10x performance jump after all. Twitter had this problem a while back, essentially their DB server got overloaded but it was already a 8 CPU, 64GB machine and despite having lots of money they couldn't quickly solve the problem, because you couldn't really get a bigger system. Facebook knows how to scale, they want to cut costs where they can to become (more) profitable.
deleted 17y ago
[deleted]

lallysingh 17y ago

It's more like scalability is the derivative of efficiency, for N_1 and N_2 user counts, scalability = (efficiency(N_2) - efficiency(N_1))/(N_2 - N_1)