5 ms·

While you’re not wrong, it’s not necessarily under Tesla’s control if they can do so (do they build and manage their own map data files?) and even if it was, ma

by p49k 9y ago

While you’re not wrong, it’s not necessarily under Tesla’s control if they can do so (do they build and manage their own map data files?) and even if it was, managing an update that supports delta patches is its own headache that comes with extra engineering and testing costs, so maybe in the end the extra cost would be comparable? We’re only talking about 200k clients here, unlike Google in which each byte of bandwidth reduction is multiplied by hundreds of millions of phones.

icebraining 9y ago
You don't need to build your own files to do a delta. You just take the old file and the new one, and you calculate a binary diff using cperciva's bsdiff or Google's courgette. Then on the car you take the old file and the diff to generate the new file.
- unwind 9y ago
  Off-topic, but thanks for reminding me about bsdiff [1], it's quite cool. Not something I have had a reason to use, but something I enjoy knowing about. Also, it's wonderful that the web page about it uses a Pentium at 200 MHz as the performance reference platform (at 45 KB/s). :) [1] http://www.daemonology.net/bsdiff/ http://www.daemonology.net/bsdiff/
- codeulike 9y ago
  But you have to carefully check which version is currently there before you apply the delta, to make sure it's applicable. Also make sure previous delta was fully applied and not stopped halfway through etc etc. It really is not as trivial as you make it sound, hence the extra engineering burden mentioned in comment above.
  - iainmerrick 9y ago
    OK, but if they're a good member of the tech community, they should put in that effort and/or charge their own customers appropriately. Not just punt on it and exploit somebody else's free service.
    - codeulike 9y ago
      But then they also need to download other large files regularly. So I think their policy is to tell people to do it over wifi, and most people can do that, because their car sits in a garage or near a house all night. Seems sensible, no? Why take the risk of messing about with deltas when most customers manage fine.
    - p49k 9y ago
      They are already much better members of the tech community than most car manufacturers. I have to make an appointment with my dealer and leave my car there for a few hours if I want a map update for my navigation system and I have to pay an unreasonable amount of money for it. I think what people are asking here is too much; it’s not an unrealistic expectation that someone to find wifi occasionally in order to receive free updates.
  - icebraining 9y ago
    You already have to check if the file was correctly downloaded over Wifi and not stopped halfway or tampered with. There's no new requirement here. You do have to compare if the old file is the correct, but not only is that extremely basic (I mean, it's comparing a filename), even if you manage to muck it up, the previously mentioned check will make sure the incorrectly generated file won't be applied, since the signature won't be valid.
    - codeulike 9y ago
      You're assuming each different version of this map database will have a different filename? I dont think you've thought this through. Everything in software engineering seems simple if you dont look at the details. You're saying it would be easy to do deltas. I'm saying its not as easy as you think, and secondly why should they bother when there's probably a thousand more important requirements on their to-do list right now. Thats whats real-world projects are like.
      - icebraining 9y ago
        You're assuming each different version of this map database will have a different filename? It'll have whatever Tesla wants it to have. Even if they receive the file as a binary blob, they can attach whatever metadata they want when transferring it to the car. A filename would just be what I'd use, but the specific format is irrelevant. Everything in software engineering seems simple if you dont look at the details. (...) And some actually are. But in any case, I never actually said it was simple. I rebutted specific reasons you gave. Is it complicated for other reasons? Sure, maybe, who knows.
- TorKlingberg 9y ago
  That may not work if the file is compressed, depending on how the compression works.
- p49k 9y ago
  An effective delta-based update strategy requires planning and implementation that anticipates such a system; otherwise you’re going to end up with diffs that are not significantly smaller than the original files.

by p49k 9y ago

icebraining 9y ago

You don't need to build your own files to do a delta. You just take the old file and the new one, and you calculate a binary diff using cperciva's bsdiff or Google's courgette. Then on the car you take the old file and the diff to generate the new file.

unwind 9y ago
Off-topic, but thanks for reminding me about bsdiff [1], it's quite cool. Not something I have had a reason to use, but something I enjoy knowing about. Also, it's wonderful that the web page about it uses a Pentium at 200 MHz as the performance reference platform (at 45 KB/s). :) [1] http://www.daemonology.net/bsdiff/ http://www.daemonology.net/bsdiff/
codeulike 9y ago
But you have to carefully check which version is currently there before you apply the delta, to make sure it's applicable. Also make sure previous delta was fully applied and not stopped halfway through etc etc. It really is not as trivial as you make it sound, hence the extra engineering burden mentioned in comment above.
- iainmerrick 9y ago
  OK, but if they're a good member of the tech community, they should put in that effort and/or charge their own customers appropriately. Not just punt on it and exploit somebody else's free service.
  - codeulike 9y ago
    But then they also need to download other large files regularly. So I think their policy is to tell people to do it over wifi, and most people can do that, because their car sits in a garage or near a house all night. Seems sensible, no? Why take the risk of messing about with deltas when most customers manage fine.
  - p49k 9y ago
    They are already much better members of the tech community than most car manufacturers. I have to make an appointment with my dealer and leave my car there for a few hours if I want a map update for my navigation system and I have to pay an unreasonable amount of money for it. I think what people are asking here is too much; it’s not an unrealistic expectation that someone to find wifi occasionally in order to receive free updates.
- icebraining 9y ago
  You already have to check if the file was correctly downloaded over Wifi and not stopped halfway or tampered with. There's no new requirement here. You do have to compare if the old file is the correct, but not only is that extremely basic (I mean, it's comparing a filename), even if you manage to muck it up, the previously mentioned check will make sure the incorrectly generated file won't be applied, since the signature won't be valid.
  - codeulike 9y ago
    You're assuming each different version of this map database will have a different filename? I dont think you've thought this through. Everything in software engineering seems simple if you dont look at the details. You're saying it would be easy to do deltas. I'm saying its not as easy as you think, and secondly why should they bother when there's probably a thousand more important requirements on their to-do list right now. Thats whats real-world projects are like.
    - icebraining 9y ago
      You're assuming each different version of this map database will have a different filename? It'll have whatever Tesla wants it to have. Even if they receive the file as a binary blob, they can attach whatever metadata they want when transferring it to the car. A filename would just be what I'd use, but the specific format is irrelevant. Everything in software engineering seems simple if you dont look at the details. (...) And some actually are. But in any case, I never actually said it was simple. I rebutted specific reasons you gave. Is it complicated for other reasons? Sure, maybe, who knows.
TorKlingberg 9y ago
That may not work if the file is compressed, depending on how the compression works.
p49k 9y ago
An effective delta-based update strategy requires planning and implementation that anticipates such a system; otherwise you’re going to end up with diffs that are not significantly smaller than the original files.