transfer a codespaces dev mysql instance to tmpfs.

memorize_mysql

#!/usr/bin/env ruby
# frozen_string_literal: true

require "fileutils"

module MemorizeMysql
  WD = "/var/lib"
  MYSQL = "/var/lib/mysql"

  def self.call
    if File.readlines("/etc/mtab").any? { |line| line.include?("/var/lib/mysql") }
      die "already in memory"
    end

    if Process.euid != 0
      exec("sudo #{$PROGRAM_NAME}")
    end

    Dir.chdir(WD)

    run "supervisorctl stop mysql"
    tarball = nil

    if !Dir.empty?(MYSQL)
      tarball = "mysql-#{Time.now.to_i}.tar.xz"
      puts "mysql dir is nonempty, archiving it to #{tarball}"
      run "tar cJf #{tarball} #{MYSQL}"
      run "rm -r #{MYSQL}/*"
    end

    tarball ||= Dir['/var/lib/mysql*.tar.xz'].max_by { |x| File.mtime(x) }

    if !tarball
      die "could not find tarball to reinflate"
    end

    run "mount -t tmpfs -o size=5G tmpfs #{MYSQL}"
    run "tar xf #{tarball}"
    FileUtils.chown_R "mysql", "mysql", MYSQL
    FileUtils.chmod 0700,  MYSQL
    run("supervisorctl start mysql")
  end

  def self.run(cmd)
    puts "-> #{cmd}"
    system(cmd, exception: true)
  end

  def self.die(msg)
    puts msg
    exit 1
  end
end

if __FILE__ == $PROGRAM_NAME
  MemorizeMysql.call
end

See https://github.com/brasic/moneta for a slightly more useful version of this