fe9lix

ANNOUNCEMENT

I have moved this over to the Tech Interview Cheat Sheet Repo and has been expanded and even has code challenges you can run and practice against!

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Turning PostgreSQL into a queue serving 10,000 jobs per second

RDBMS-based job queues have been criticized recently for being unable to handle heavy loads. And they deserve it, to some extent, because the queries used to safely lock a job have been pretty hairy. SELECT FOR UPDATE followed by an UPDATE works fine at first, but then you add more workers, and each is trying to SELECT FOR UPDATE the same row (and maybe throwing NOWAIT in there, then catching the errors and retrying), and things slow down.

On top of that, they have to actually update the row to mark it as locked, so the rest of your workers are sitting there waiting while one of them propagates its lock to disk (and the disks of however many servers you're replicating to). QueueClassic got some mileage out of the novel idea of randomly picking a row near the front of the queue to lock, but I can't still seem to get more than an an extra few hundred jobs per second out of it under heavy load.

So, many developers have started going straight t

Falsehoods programmers believe about prices

You can store a price in a floating point variable.
All currencies are subdivided in 1/100th units (like US dollar/cents, euro/eurocents etc.).
All currencies are subdivided in decimal units (like dinar/fils)
All currencies currently in circulation are subdivided in decimal units. (to exclude shillings, pennies) (counter-example: MGA)
All currencies are subdivided. (counter-examples: KRW, COP, JPY... Or subdivisions can be deprecated.)
Prices can't have more precision than the smaller sub-unit of the currency. (e.g. gas prices)
For any currency you can have a price of 1. (ZWL)
Every country has its own currency. (EUR is the best example, but also Franc CFA, etc.)

How to connect an iOS device to your computer via a SOCKS proxy

Say you're running a virtual machine on your work computer. Say this machine, for whatever reason, can only connect to the internet over NAT - as in, it does not get it's own IP address. Say this VM is running a webserver, and you need a device outside of your computer to connect to it.

If only there was a way to get your work computer to 'share' it's network, so that you could get at that VM… Here's how you do it!

For all instructions, I assume your work computer is a mac

Get your computer's IP address:

	// Just before switching jobs:
	// Add one of these.
	// Preferably into the same commit where you do a large merge.
	//
	// This started as a tweet with a joke of "C++ pro-tip: #define private public",
	// and then it quickly escalated into more and more evil suggestions.
	// I've tried to capture interesting suggestions here.
	//
	// Contributors: @r2d2rigo, @joeldevahl, @msinilo, @_Humus_,
	// @YuriyODonnell, @rygorous, @cmuratori, @mike_acton, @grumpygiant,