Goals: Add links that are reasonable and good explanations of how stuff works. No hype and no vendor content if possible. Practical first-hand accounts of models in prod eagerly sought.

This post is in response to the WeekendDevPuzzle of 2022-02-05, which has submissions from people who chose to share their perspectives on the puzzle. I'll be linking this post to this Twitter thread, to avoid polluting the original one.
We all have a mental model of how something works. For today's puzzle, the relevant mental model is: the same series of instructions should result in the same time of execution. The astute would be quick to add: in non-noisy environments only. And they'd be correct.
But then where's the flaw in this model? Let's start.
The puzzle seems simple enough: a program reads in an array of integers, and counts how many of them are less than a threshold (another parameter to the program). We've been informed that there are no noisy-neighbour issues, and we're measu
GOCMD=go | |
GOTEST=$(GOCMD) test | |
GOVET=$(GOCMD) vet | |
BINARY_NAME=example | |
VERSION?=0.0.0 | |
SERVICE_PORT?=3000 | |
DOCKER_REGISTRY?= #if set it should finished by / | |
EXPORT_RESULT?=false # for CI please set EXPORT_RESULT to true | |
GREEN := $(shell tput -Txterm setaf 2) |
Author: Chris Lattner
import java.util.Arrays; | |
class NonCapturing { | |
public static void main(String... args) { | |
run(new Runnable() { | |
@Override public void run() { | |
System.out.println("Hey!"); | |
} | |
}); | |
} |
<?xml version="1.0" encoding="utf-8"?> | |
<resources> | |
<!-- google's material design colours from | |
http://www.google.com/design/spec/style/color.html#color-ui-color-palette --> | |
<!--reds--> | |
<color name="md_red_50">#FFEBEE</color> | |
<color name="md_red_100">#FFCDD2</color> | |
<color name="md_red_200">#EF9A9A</color> |
import android.content.Context; | |
import android.graphics.Canvas; | |
import android.graphics.Color; | |
import android.graphics.Matrix; | |
import android.graphics.Paint; | |
import android.graphics.Path; | |
import android.graphics.RectF; | |
import android.util.AttributeSet; | |
import android.view.View; | |
import android.view.animation.AccelerateDecelerateInterpolator; |
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
Latency Comparison Numbers (~2012) | |
---------------------------------- | |
L1 cache reference 0.5 ns | |
Branch mispredict 5 ns | |
L2 cache reference 7 ns 14x L1 cache | |
Mutex lock/unlock 25 ns | |
Main memory reference 100 ns 20x L2 cache, 200x L1 cache | |
Compress 1K bytes with Zippy 3,000 ns 3 us | |
Send 1K bytes over 1 Gbps network 10,000 ns 10 us | |
Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD |