This always seems intuitive to me. You see a single queue feeding multiple processors fairly often such as in banks and security queues at airports. They seem "fairer" to me as you are not disadvantaged by picking the "wrong" queue through a bad prediction. In a classic supermarket queuing scenario, you could pick the shortest queue but find that the person in front is incredibly slow, so the three people who came to checkout after you at other checkouts progress through the process faster. This is first come, first served.
A single line to 3 cashiers is ~3x faster than a separate line for each cashier
151–160 of 172 posts
Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier
#152Earlier quoted context omitted.
Not trying to be condescending but doesn't it surprise anyone here that this is _not_ obvious? At least on this site, there are still people doubting or debating this. So I am wondering why don't stores do this already. And I believe it is because of perceptions. They understand that time will be saved, however, they realize that most people will be scared by a long line. One long line that moves fast will still appe…
It's another instance of "people are stupid". Yes, for any educated person it's obvious that one line is faster, that's the first thing about queueing theory, but most people don't know the first thing about queueing theory. Other instances of "people are stupid" leading to poor design: * Some cars come with a CVT (continuously variable transmission) rather than having to shift gears. The audible pitch of the engine…
It's not at all obvious to me that one line is always faster (but then I only have a master's degree :-)). It might be faster in some situations, maybe slower in others.
In particular, the one-line system might significantly increase the average distance between (first-in-line) customer and nearest free cashier. Also, when there's a lot of cashiers, the customer might take more time to notice where is the nearest free cashier. I saw that happening the last time I checked-in for a flight.
In contrast, at immigration there is a long, single line but also short lines (1 to 2 persons) in front of each "cashier". These work as "caches" that minimize the delay I mentioned above.
Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier
#153FYI: This is an example of the branch of mathematics called queueing theory. http://en.wikipedia.org/wiki/Queueing_theory It's a fascinating study requiring a good knowledge of probability to use beyond the simplified models. It turns out from the math that throughput using a single queue is better than using multiple queues.
Not trying to be condescending but doesn't it surprise anyone here that this is _not_ obvious? At least on this site, there are still people doubting or debating this. So I am wondering why don't stores do this already. And I believe it is because of perceptions. They understand that time will be saved, however, they realize that most people will be scared by a long line. One long line that moves fast will still appe…
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Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier
#154How many times have you been standing in a queue with the money in your hand, wishing you could just drop the money and get out, who cares about change, you just want to get the hell out of here.
This is my proposal for a "no change given" line.
You walk up, you plop down at least the amount of money that the items are worth, they quickly scan the Good for business as they would collect many extra $$ from impatient shoppers, and good for shoppers who are impatient. All-round good.
Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier
#155people like me that have been in telecom for 30+ year are amazed that this garnered 146 comments. Erlang-C, no not the language Erlang, before that...
Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier
#156Earlier quoted context omitted.
Except that the "primary" queue doesn't feed into the shortest register queue, it feeds into the register queue that the person at the front of the primary queue anticipates will empty the fastest. That's the premise that underlies the whole article: people get in the line they predict will move the fastest, and everyone uses different variables and judgment to make that prediction. Those variables and those predicti…
>everyone uses different variables and judgment to make that prediction. Those variables and those predictions don't show up when your model is based on distributions. Sorry but that's simply not true. everyone uses different variables and judgment to make a phone call, yet phone calls follow an exponential distribution! everyone uses different variables and judgment to hit the internet, yet network traffic follows a…
"Phone calls follow an exponential distribution"
I'm confused as to the meaning there. What is it about phone calls that follow an exponential distribution? Their duration? Their quantity per capita per time of day?
Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier
#157Back in 1989 as one of our projects in a data structures course, we solved this problem and reached the same conclusions. We did it using Pascal!
There are other factors which aren't typically considered. The latency of someone walking from the head of the single queue to the cashier each time matters, especially if the person at the front isn't alert or is confused by trying to figure out which till to go to. People are smart enough to pick short queues to join and there is no latency. Also psychology, nobody wants to join a long queue even if it moves fast, they go to another store.
Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier
#158Earlier quoted context omitted.
It's another instance of "people are stupid". Yes, for any educated person it's obvious that one line is faster, that's the first thing about queueing theory, but most people don't know the first thing about queueing theory. Other instances of "people are stupid" leading to poor design: * Some cars come with a CVT (continuously variable transmission) rather than having to shift gears. The audible pitch of the engine…
It's not at all obvious to me that one line is always faster (but then I only have a master's degree :-)). It might be faster in some situations, maybe slower in others. In particular, the one-line system might significantly increase the average distance between (first-in-line) customer and nearest free cashier. Also, when there's a lot of cashiers, the customer might take more time to notice where is the nearest fre…
As others have mentioned, one line feeding small cache lines is probably closer to reality, for the reasons that you mention -- buffering so that the cashier is always occupied.
The main goal is to prevent a single "price check" from jamming an entire line of people -- keep the queues at each station as small as possible so that most customers can route around the blockage.
Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier
#159When I went out for fast food as a kid with my grandfather (an engineer), he would send me and my brother and sister to each stand in one line. He would then come over to join whomever got to the front first. That was my first lesson in queueing theory ...
Re: A single line to 3 cashiers is ~3x faster than a separate line for each cashier
#160Most of the grocery stores in my area have installed self-checkout systems that are especially great if you just have a handful of items that all have UPCs (no produce or bagged bulk), don't have any items requiring an age check and possess at least the intelligence of a fifth grader. I mention this not just because it's relevant to the idea of waiting in line at a store, but because in every store where I've seen th…
In stores in Sweden with self-scanning there are scales in the vegetable department that will print out an appropriate UPC for you to scan (with your hand-held scanner). People who don't self-scan are also recommended to use these to let the cashier avoid weighing all goods. You still have to contact a cashier for age-restricted merchandise such as beer and tobacco, though.
To self-scan you need to register with the store, and in the beginning you're manually checked a couple of times. They track how many errors you have and on what kind of merchandise, and determine how trust-worthy you are and how often you should be manually checked.
I can't remember if this was already implemented or just a suggestion from somewhere, but the self-scanning devices could track your location in the store, both to analyze customer behaviour but also to monitor any suspicious activity. If you spend 15 minutes in the electronics department without scanning anything, maybe that warrants a manual check.
As a side note, I wonder how much time self-scanning and self-checkout really saves in the end, for the consumer, and how much of it is just letting us do more unpaid labour under the impression of efficiency.