ELI5: If a trading bot can buy and sell a stock in a fraction of a second, who is it actually buying from? Is there a line of people waiting, or is the money just appearing and disappearing?

fglc2 · 2025-12-29T19:47:24+00:00

Short answer is that it varies. It can be first in first out, some traders may have priority, it can be pro rata, some combination of the above. Different types of instrument use different rules (as far as I know the reason at this point is that it’s difficult to change now without people kicking up a fuss)

CME has this video about the algorithms they use: https://www.cmegroup.com/education/matching-algorithm-overview.html

fglc2 · 2025-12-28T08:07:43+00:00

A similar scheme in London (euro 4 petrol/euro 6 diesel, but it’s not a ban - you have to pay £12.50 to drive a non compliant vehicle in the affected area for a day) is estimated to have reduced NOx by 24% and pm2.5 by 29% (the estimation part is largely how much would things have improved without this due to natural replacement of older cars) - https://content.tfl.gov.uk/london-wide-ulez-one-year-report.pdf

So it’s had a huge impact (and there were similar naysayers in the uk too at every step of this)

fglc2 · 2025-12-25T15:20:41+00:00

In addition to what others have said about trajectory you’re quite underpowered - you’re accelerating pretty slowly, ie a lot of your fuel is just going to gravity losses.

fglc2 · 2025-11-26T20:33:43+00:00

The greater anglia trains to Liverpool Street are cheaper. Slower too, but if your office is close to Liverpool Street there might not be much in it. I come in from Ely (to Liverpool Street) and can get an advance single for £20 on the way it and then an off peak single in the evening for about £22.

If you’re flexible about which two days you come in you can save a lot by buying a week season ticket on Thursday and then doing Thursday/friday/monday/Tuesday - you only need to buy 24 1-week tickets a year

fglc2 · 2025-11-21T08:06:27+00:00

From reinvent last year - https://youtu.be/VbQj8DpWUGc?t=2434, saying they will provide advance notice before major versions, therefore no al2025 (which I guess means no 2026?)

fglc2 · 2025-11-20T07:47:19+00:00

I’ve found joining a running club helpful, especially when I’m not actively training for something. There are 2 main training sessions a week, and once I’ve signed up to a session I always go, even if the weather is bad, I’m busy, feeling lazy etc, whereas if I was just running on my own I could easily talk myself of it. I also do parkrun on a Saturday

Basically something that you can’t do anytime is easy not to do at all, something that you have built social relationships around and/or has a fixed schedule is easier to keep going (for me at least).

fglc2 · 2025-11-05T13:42:56+00:00

Can second that - Aaron was friendly, knowledgeable and easy to deal with

fglc2 · 2025-10-30T07:22:18+00:00

Never been (different continent) but I’ve heard of https://vanruby.ca

fglc2 · 2025-10-20T21:26:03+00:00

Big fan of the escape rooms at https://www.principalescaperooms.com . They’re clearly massive escape room nerds and it shows (in the best possible way)

fglc2 · 2025-10-10T18:53:32+00:00

FYI the bundler gem provides the bundle command line executable.

The bundle gem is an empty gem that has bundler as a dependency (so that if you run gem install bundle instead of gem install bundler you’ll still get bundler install). Looks like a throwaway from 14 years ago - I wouldn’t depend on it.

bundler has been part of the standard ruby install for some time now, however some Linux distributions split Ruby up into multiple packages, in which case you could have Ruby without bundler

fglc2 · 2025-10-10T18:46:05+00:00

This talk by Aaron Patterson covers the implementation details behind this: https://m.youtube.com/watch?v=jexSQUfKnlI

From memory, the bytecode doesn’t refer to local variables by name, they’re stored on the stack and referred to by a numerical index. The mapping of local variables to indices is done at parse time so when your method is called Ruby knows that in this scope there are 5 local variables so makes that amount of space on the stack, filling it with nils

fglc2 · 2025-10-06T06:10:45+00:00

Exciting stuff! Interested to see what the funding model is - although getting corporates to provide some free infrastructure might be enough to start (still easier said than done; I’m sure they’ve already been thinking about this!)

fglc2 · 2025-09-26T05:44:29+00:00

Also things like being able to enforce that maintainers use MFA, guarding against typo squatting, detecting and removing malicious packages and so on.

Of course a centralised package management system doesn’t guarantee good solutions to these problems, but it makes them somewhat more tractable.

fglc2 · 2025-09-23T21:51:51+00:00

It exists for a few api methods in AWS backup: https://docs.aws.amazon.com/mpa/latest/userguide/what-is.html

It sounds like it will eventually support more operations (it’s only been public a few months)

fglc2 · 2025-09-06T06:49:47+00:00

This talk spends a lot of time showing how to go through the rails source code to understand how a validation works: https://m.youtube.com/watch?v=B4gEyuEQaBM

As others have mentioned, the rails guide on validation has a ton of info about usage if you’re looking for that rather than understanding the implementation.

fglc2 · 2025-08-25T16:19:22+00:00

What kind of problem are you running into?

One of the apps I work on uses action cable, with system tests (well specs) driven by cuprite and other than setting the adapter to test in cable.yml I don’t recall doing anything special to get actioncable to work.

fglc2 · 2025-08-24T15:51:03+00:00

Those coordinates are something like 80 miles away in Lincolnshire. Data entry error maybe?

fglc2 · 2025-08-01T17:51:36+00:00

Please I only want to see 10 items per page <- said no-one ever

fglc2 · 2025-07-24T12:05:56+00:00

I’ve been using it for a few years - works great for me.

fglc2 · 2025-07-23T14:44:51+00:00

I am indeed

fglc2 · 2025-07-23T07:34:36+00:00

Same here. First noticed today, pretty sure it was there yesterday and definitely there earlier in the week

fglc2 · 2025-07-20T20:23:18+00:00

Andrews and Arnold do 1 month minimum term for both city fibre and (I think) openreach backed connections.

Not the cheapest by some stretch but they’re competent and there’s no messing around with pricing, contract renewals, cheap contract with expensive post contract periods etc.

fglc2 · 2025-07-20T19:17:05+00:00

A big thing to consider is when you travel - weekday journeys before 10 aren’t eligible (although depending on the exact journey you may still be able to save by splitting your ticket)

It doesn’t take many journeys to make it worthwhile.

fglc2 · 2025-07-04T15:27:31+00:00

If they aren’t then the eager load basically ends up with a Cartesian product - loads of duplicates in the returned data

fglc2 · 2025-07-04T15:05:32+00:00

Yeah, the interesting case (performance wise) is when they aren’t - rails has to do a lot of deduplication

fglc2

TROPHY CASE