6 ms·

The real irony here is that airlines actually do something very much like overcommit & OOM killer when it comes to reservations, and for precisely the same reas

by cbsmith 13y ago

The real irony here is that airlines actually do something very much like overcommit & OOM killer when it comes to reservations, and for precisely the same reasons: they know that not all the reservations will be used at the same time, but sometimes they do end up double booked, so then someone has to be kicked off the flight.

tcoppi 13y ago
Precisely. The OOM killer has its uses, and while it's debatable if it is suited for this workload or that workload, it is easily tunable for specific use cases, and you can disable it altogether if you'd like the classic behavior.
lucaspiller 13y ago
> sometimes they do end up double booked Sometimes is pretty much all of the time. My SO works as cabin crew for one of the large airlines you will have heard of, and they typically always overcommit. It isn't just because they are greedy and want lots of money though (well I guess it kind of is). As you said, they know some people won't turn up, but also they may decide to change the class of the airline (economy and business -> economy, business and first) depending on how people book or what aircraft are available on the day.
- ubernostrum 13y ago
  but also they may decide to change the class of the airline (economy and business -> economy, business and first) depending on how people book or what aircraft are available on the day. United is infamous for this, prompting a sound piece of advice: if for some reason you're in first class on a flight scheduled for an A320, don't take a seat in row 3, since odds are high it'll be swapped to an A319 (which only has two rows in F) day of the flight. In theory there's a pecking order for who gets downgraded in that case (first, anyone who moved up to F on a status upgrade, then the paid F fares starting with whoever was latest to check in), but in practice the gate agent just bumps row 3 and calls it a day.
  - mherdeg 13y ago
    I feel like aircraft substitutions are more likely to happen for operational reasons (the A320 they wanted to commit is unavailable because of mx/wx, most likely, and instead of taking a delay, they pull an A319). Some carriers do seem to use last-minute equipment swaps for yield management, but I feel like for UA, doing this is not a good idea — they burn a lot of time re-assigning seats and refunding E+ fees, etc. after a 320->319 downgrade, so I think it's something they try to avoid because it's costly to deviate from the planned equipment. I think the parent poster was in part referring to operational upgrades (very common at British Airways — they will dramatically oversell the Y cabin and op-up people into J/F as needed), which don't necessarily require an equipment swap. Another option uniquely available to European carriers that you might not have seen in the U.S. is to adjust the number of J/Y seats in an aircraft: on most intra-Europe flights, the "business-class cabin" is the same seats as the coach cabin, but with a blocked middle seat and a movable divider so you know where Y starts. (Come to think of it, I guess BA will sometimes swap equipment to a flight with fewer classes of service — for example, the LHR-DME route can lose its lie-flat Club World seats overnight sometimes after unplanned equipment swaps — but I don't think BA does this for yield management, because it's costly to them to have to pay refunds to people they've inconvenienced.)
    - ubernostrum 13y ago
      I don't know why United does it, just that the A320/A319 swap is so common with them that on frequent-flyer forums it often gets a stickied thread with tips on what to do, warning signs, etc. Hence the advice about never taking a seat in row 3 (and for economy passengers, never booking into the last couple rows of the aircraft, since those seats don't exist on the 319).
      - mherdeg 13y ago
        There's also a counterintuitive "always choose row 3" option, where you make yourself more likely to be downgraded but also more likely to be offered a travel voucher under United's fairly generous distance-based compensation policy (internal documentation "GG OVS DOWNGRADE").
- sliverstorm 13y ago
  It isn't just because they are greedy and want lots of money Certainly not in the current airline environment. Even with a perfectly loaded plane, they only make a little money, and you can't plan for a perfectly loaded plane with any kind of confidence without double-booking.
- cbsmith 13y ago
  > My SO works as cabin crew for one of the large airlines you will have heard of, and they typically always overcommit. I phrased what I said poorly. They always allow overcommit, but they try to work it out so that on average they efficiently make use of their seats without constantly having to give people giveaways and bad customer experiences.
bruceboughton 13y ago
Except they do this before the flight, not once you've taken off. Though Ryanair could well be heading down this route [1] [1] http://www.independent.ie/irish-news/three-ryanair-mayday-calls-go-out-on-same-day-26886838.html http://www.independent.ie/irish-news/three-ryanair-mayday-ca...
- Kliment 13y ago
  Very clever, that, once you think about it. "The on-time airline" running late, stuck in holding pattern, claim you're out of fuel, get landing priority, no more delay. About as classy as the other Ryanair tactics.
  - bruceboughton 13y ago
    I would agree except that it seems to go deeper than that. Pilots are ranked by how little spare fuel they take. If they dare to take too much spare fuel they have to write a memo to management explaining why.
  - taloft 13y ago
    Actually, they were low on fuel, because the company was forcing captains to carry only the company-approved minimum under threat of discipline.
    - gnaffle 13y ago
      It's not company-approved, it's regulator-approved, which is designed to be sufficient. Airlines have no reason to go above that, except for planning reasons (eg you might want to add some extra fuel to have the option to fly faster on some legs to make up for delays). So I wouldn't expect Ryanair to carry less fuel than other airlines. The only exception that airlines will sometimes do is to juggle around destination and alternate airports so that they can save some fuel on that (you have to have enough fuel to reach an alternate airport, and then 45 minutes in addition to that).
      - 13y ago
mhb 13y ago
Also, Samoa Air charges by the pound. Maybe there could be some kind of auction system for "heavier" processes to "pay" more to keep running. http://business.time.com/2013/04/08/air-travel-by-the-pound-and-other-odd-airline-pricing-schemes/ http://business.time.com/2013/04/08/air-travel-by-the-pound-...
mikeash 13y ago
That's more analogous to the strategy of pausing processes which require memory when there isn't any available, and then resuming them once memory becomes available. The airline still lets you complete your trip when they bump you from a flight, you just have to wait until capacity becomes available for you. The problem with translating that approach to OSes is that you can easily deadlock the entire system.
- cbsmith 13y ago
  It depends on circumstance. For a lot of people, having their flight canceled and having to switch to another is all but catastrophic. You basically have to restart and build a new travel plan, and much of what you set out to accomplish gets lost. So... a lot like killing a process.
BrainInAJar 13y ago
Yes, but that's more like fork or malloc failing in the first place than letting you run and then randomly killing something when the system gets overcomitted

by cbsmith 13y ago

tcoppi 13y ago

Precisely. The OOM killer has its uses, and while it's debatable if it is suited for this workload or that workload, it is easily tunable for specific use cases, and you can disable it altogether if you'd like the classic behavior.

lucaspiller 13y ago

> sometimes they do end up double booked Sometimes is pretty much all of the time. My SO works as cabin crew for one of the large airlines you will have heard of, and they typically always overcommit. It isn't just because they are greedy and want lots of money though (well I guess it kind of is). As you said, they know some people won't turn up, but also they may decide to change the class of the airline (economy and business -> economy, business and first) depending on how people book or what aircraft are available on the day.

ubernostrum 13y ago
but also they may decide to change the class of the airline (economy and business -> economy, business and first) depending on how people book or what aircraft are available on the day. United is infamous for this, prompting a sound piece of advice: if for some reason you're in first class on a flight scheduled for an A320, don't take a seat in row 3, since odds are high it'll be swapped to an A319 (which only has two rows in F) day of the flight. In theory there's a pecking order for who gets downgraded in that case (first, anyone who moved up to F on a status upgrade, then the paid F fares starting with whoever was latest to check in), but in practice the gate agent just bumps row 3 and calls it a day.
- mherdeg 13y ago
  I feel like aircraft substitutions are more likely to happen for operational reasons (the A320 they wanted to commit is unavailable because of mx/wx, most likely, and instead of taking a delay, they pull an A319). Some carriers do seem to use last-minute equipment swaps for yield management, but I feel like for UA, doing this is not a good idea — they burn a lot of time re-assigning seats and refunding E+ fees, etc. after a 320->319 downgrade, so I think it's something they try to avoid because it's costly to deviate from the planned equipment. I think the parent poster was in part referring to operational upgrades (very common at British Airways — they will dramatically oversell the Y cabin and op-up people into J/F as needed), which don't necessarily require an equipment swap. Another option uniquely available to European carriers that you might not have seen in the U.S. is to adjust the number of J/Y seats in an aircraft: on most intra-Europe flights, the "business-class cabin" is the same seats as the coach cabin, but with a blocked middle seat and a movable divider so you know where Y starts. (Come to think of it, I guess BA will sometimes swap equipment to a flight with fewer classes of service — for example, the LHR-DME route can lose its lie-flat Club World seats overnight sometimes after unplanned equipment swaps — but I don't think BA does this for yield management, because it's costly to them to have to pay refunds to people they've inconvenienced.)
  - ubernostrum 13y ago
    I don't know why United does it, just that the A320/A319 swap is so common with them that on frequent-flyer forums it often gets a stickied thread with tips on what to do, warning signs, etc. Hence the advice about never taking a seat in row 3 (and for economy passengers, never booking into the last couple rows of the aircraft, since those seats don't exist on the 319).
    - mherdeg 13y ago
      There's also a counterintuitive "always choose row 3" option, where you make yourself more likely to be downgraded but also more likely to be offered a travel voucher under United's fairly generous distance-based compensation policy (internal documentation "GG OVS DOWNGRADE").
sliverstorm 13y ago
It isn't just because they are greedy and want lots of money Certainly not in the current airline environment. Even with a perfectly loaded plane, they only make a little money, and you can't plan for a perfectly loaded plane with any kind of confidence without double-booking.
cbsmith 13y ago
> My SO works as cabin crew for one of the large airlines you will have heard of, and they typically always overcommit. I phrased what I said poorly. They always allow overcommit, but they try to work it out so that on average they efficiently make use of their seats without constantly having to give people giveaways and bad customer experiences.

bruceboughton 13y ago

Except they do this before the flight, not once you've taken off. Though Ryanair could well be heading down this route [1] [1] http://www.independent.ie/irish-news/three-ryanair-mayday-calls-go-out-on-same-day-26886838.html http://www.independent.ie/irish-news/three-ryanair-mayday-ca...

Kliment 13y ago
Very clever, that, once you think about it. "The on-time airline" running late, stuck in holding pattern, claim you're out of fuel, get landing priority, no more delay. About as classy as the other Ryanair tactics.
- bruceboughton 13y ago
  I would agree except that it seems to go deeper than that. Pilots are ranked by how little spare fuel they take. If they dare to take too much spare fuel they have to write a memo to management explaining why.
- taloft 13y ago
  Actually, they were low on fuel, because the company was forcing captains to carry only the company-approved minimum under threat of discipline.
  - gnaffle 13y ago
    It's not company-approved, it's regulator-approved, which is designed to be sufficient. Airlines have no reason to go above that, except for planning reasons (eg you might want to add some extra fuel to have the option to fly faster on some legs to make up for delays). So I wouldn't expect Ryanair to carry less fuel than other airlines. The only exception that airlines will sometimes do is to juggle around destination and alternate airports so that they can save some fuel on that (you have to have enough fuel to reach an alternate airport, and then 45 minutes in addition to that).
    - 13y ago

mhb 13y ago

Also, Samoa Air charges by the pound. Maybe there could be some kind of auction system for "heavier" processes to "pay" more to keep running. http://business.time.com/2013/04/08/air-travel-by-the-pound-and-other-odd-airline-pricing-schemes/ http://business.time.com/2013/04/08/air-travel-by-the-pound-...

mikeash 13y ago

That's more analogous to the strategy of pausing processes which require memory when there isn't any available, and then resuming them once memory becomes available. The airline still lets you complete your trip when they bump you from a flight, you just have to wait until capacity becomes available for you. The problem with translating that approach to OSes is that you can easily deadlock the entire system.

cbsmith 13y ago
It depends on circumstance. For a lot of people, having their flight canceled and having to switch to another is all but catastrophic. You basically have to restart and build a new travel plan, and much of what you set out to accomplish gets lost. So... a lot like killing a process.

BrainInAJar 13y ago

Yes, but that's more like fork or malloc failing in the first place than letting you run and then randomly killing something when the system gets overcomitted