emhoracek

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emhoracek

Using PostgreSQL Advisory Locks in Haskell

Recently two different administrative users of a Haskell app I maintain started a long-running background job at the same time. This resulted in some Bad Things happening which I would like to prevent in the future!

So I want a lock. This app runs on at least two servers at any given time, so it needs to be a distributed lock, and for Reasons (not relevant to this blogpost) I can't use our Redis cache. So the PostgreSQL database it is!

emhoracek

{-

After feeling like you've been falling for a few minutes, you look at the device's tiny screen. 
"Error: Device must be calibrated before first use. Frequency drift detected. Cannot maintain
destination lock." Below the message, the device shows a sequence of changes in frequency 
(your puzzle input). A value like +6 means the current frequency increases by 6; a value like 
-3 means the current frequency decreases by 3.

For example, if the device displays frequency changes of +1, -2, +3, +1, then starting from 
a frequency of zero, the following changes would occur:

emhoracek

On NOT Using PostgreSQL Advisory Locks in Haskell

Recently two different administrative users of a Haskell app I maintain started a long-running background job at the same time. This resulted in some Bad Things happening which I would like to prevent in the future!

So I want a lock. This app runs on at least two servers at any given time, so it needs to be a distributed lock, and for Reasons (not relevant to this blogpost) I can't use our Redis cache. So the PostgreSQL database it is!

emhoracek

<h2>The Basics</h2>
<div class="basics">
  <label>
    <span>Character name: </span>
    <input spellcheck="false" type="text" name="attr_character_name"/>
  </label>
  <label>
    <span>Pronouns: </span>
    <input spellcheck="false" type="text" name="attr_pronouns"/>

emhoracek

;;; Personal configuration -*- lexical-binding: t -*-

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