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Why some DVLA digital services don't work at night

(dafyddvaughan.uk)
124 points edent | 5 comments | 12 Jan 25 20:20 UTC | HN request time: 0s | source
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abigail95 ◴[16 Jan 25 15:43 UTC] No.42726784[source]▶
Something is missing here, why do batch jobs take 13 hours? If this thing was started on an old mainframe why isn't the downtime just 5 minutes at 3:39 AM?

Exactly how much data is getting processed?

Edit: Why does rebuilding take a decade or more? This is not a complex system. It doesn't need to solve any novel engineering challenges to operate efficiently. Article does not give much insight into why this particular task couldn't be fixed in 3 months.

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ajnin ◴[16 Jan 25 16:09 UTC] No.42727182[source]▶
The batch jobs don't take 13 hours. They're just scheduled to run some time at night where the old offices used to be closed and the jobs could be ran with some expectations regarding data stability over the period. There are probably many jobs scheduled to run at 1AM then 2AM, etc, all depending on the previous to be finished so there is some large delay to ensure that a job does not start before the previous one is finished.

As to your "not a complex system" remark, when a system is built for 60 years, piling up new rules to implement new legislation and needs over time, you tend to end up with a tangled mess of services all interdependent that are very difficult to replace piece-wise with a new shiny architecturally pure one. This is closer to a distributed monolith than a microservices architecture. In my experience you can't rebuild such a thing "in 3 months". People who believe that are those that don't realize the complexity and the extraordinary amount of specifics, special cases, that are baked into the system, and any attempt to just rebuild from scratch in a few months hits that wall and ends up taking years.

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1. Reubend ◴[16 Jan 25 21:22 UTC] No.42731073[source]▶
> In my experience you can't rebuild such a thing "in 3 months". People who believe that are those that don't realize the complexity and the extraordinary amount of specifics, special cases, that are baked into the system, and any attempt to just rebuild from scratch in a few months hits that wall and ends up taking years.

Rebuilding a legacy system doesn't require you to support every single edge case that the older system did. It's okay to start off with some minor limitations and gradually add functionality to account for those edge cases.

Furthermore, you've got a huge advantage when remaking something: you can see all the edge cases from the start, and make an ideal design for that, rather than bolting on things as you go (which is done in the case of many of these legacy systems, where functionality was added over time with dirty code in lieu of refactoring).

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2. jarofgreen ◴[16 Jan 25 22:57 UTC] No.42731976[source]▶
> Rebuilding a legacy system doesn't require you to support every single edge case that the older system did.

Depends on context.

This isn't some social media fun site where you can live with some rough edges; in this context "edge case" may be someone with an health condition who is still entitled to a drivers license; or it could be someone who normally could get one but due to a health condition really shouldn't be allowed one!

3. Analemma_ ◴[16 Jan 25 23:47 UTC] No.42732433[source]▶
This generally isn’t true in the case of government systems. For the most part they are performing tasks that are required by law, and it is not acceptable to stop some of them, even temporarily. If you’re lucky you can run the old and new systems side-by-side while the 100% feature migration occurs, but that isn’t always feasible.
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4. pixl97 ◴[17 Jan 25 00:42 UTC] No.42732778[source]▶
Ya it's funny looking at all these 'business' programmers that if the application doesn't work can just loose the customer/money to another competitor. In regulated stuff you have to serve everyone. Much worse if your systems don't work there are potential consequences where people die and or there are riots in the street.
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5. robertlagrant ◴[17 Jan 25 11:27 UTC] No.42736423{3}[source]▶
It's the opposite. Most government systems have paper-based alternatives, which they will happily tell you to use instead if their system breaks. This exact article's title should've given you a clue here. Imagine if Netflix turned off at night. That would be totally unacceptable for a business, because you're their boss, but it's fine for government.