原文链接：https://www.raydbg.com/2019/Homebrew-Update-Slow/
近期使用Homebrew去下载安装软件的时候总是卡在update阶段，时间非常久，难以忍受。记录一下解决方法，
症状
使用Homebrew安装软件的时候一直卡在Update阶段。同时发现从github.com下载文件也极度缓慢（几十 KB/s）。
问题定位
使用brew update --verbose观察update过程：
brew update --verbose
Checking if we need to fetch /usr/local/Homebrew...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/caskroom/homebrew-fonts...
Fetching /usr/local/Homebrew...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core...
Fetching /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
Fetching /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core...
remote: Enumerating objects: 337, done.
remote: Counting objects: 100% (337/337), done.
remote: Compressing objects: 100% (88/88), done.
remote: Total 298 (delta 221), reused 287 (delta 210), pack-reused 0
Receiving objects: 100% (298/298), 50.91 KiB | 39.00 KiB/s, done.
Resolving deltas: 100% (221/221), completed with 39 local objects.
From https://github.com/Homebrew/homebrew-core
65a45a9..583b7f1 master -> origin/master
remote: Enumerating objects: 179429, done.
remote: Counting objects: 100% (179429/179429), done.
remote: Compressing objects: 100% (56607/56607), done.
Receiving objects: 4% (7628/177189), 1.48 MiB | 8.00 KiB/s
发现update卡在从github仓库获取文件的过程。这个结果与手动从github下载文件慢的症状相互印证。
解决
由于问题主要是在国内网络环境github下载慢，因此尝试：
- 更换使用国内的homebrew镜像源；
- 使用代理访问github.com。
更换Homebrew源
使用以下命令更换国内阿里云上的homebrew镜像：
# 替换brew.git:
cd "$(brew --repo)"
git remote set-url origin https://mirrors.aliyun.com/homebrew/brew.git
# 替换homebrew-core.git:
cd "$(brew --repo)/Library/Taps/homebrew/homebrew-core"
git remote set-url origin https://mirrors.aliyun.com/homebrew/homebrew-core.git
# 替换homebrew-bottles:
echo 'export HOMEBREW_BOTTLE_DOMAIN=https://mirrors.aliyun.com/homebrew/homebrew-bottles' >> ~/.zshrc
source ~/.zshrc
替换后，问题依旧，继续查看日志：
brew update --verbose
Checking if we need to fetch /usr/local/Homebrew...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/caskroom/homebrew-fonts...
Fetching /usr/local/Homebrew...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core...
Fetching /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core...
From https://mirrors.aliyun.com/homebrew/homebrew-core
+ 583b7f1...8435590 master -> origin/master (forced update)
Fetching /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
Fetching /usr/local/Homebrew/Library/Taps/caskroom/homebrew-fonts...
remote: Enumerating objects: 179429, done.
remote: Counting objects: 100% (179429/179429), done.
remote: Compressing objects: 100% (56607/56607), done.
Receiving objects: 6% (11170/177189), 2.16 MiB | 30.00 KiB/s
可以看到由于homebrew-cask的仓库依然指向了Github，这个过程还是慢。阿里云的镜像站没有提供homebrew-cask，进一步搜索找到USTC镜像站，该站提供了homebrew-cask的源。使用上述同样的命令更换源：
# 替换homebrew-cask.git:
cd "$(brew --repo)"/Library/Taps/homebrew/homebrew-cask
git remote set-url origin https://mirrors.ustc.edu.cn/homebrew-cask.git
测试发现问题解决。
Note: Homebrew Bottles源的更换方法详见这里。
官方源地址：
https://github.com/Homebrew/brew.git
https://github.com/Homebrew/homebrew-core.git
https://github.com/Homebrew/homebrew-cask
使用代理
家里的路由器已经配置好了SS代理，只要简单把github.com加入到黑名单强制走proxy就可以了。然而代理速度一般，效果不及上述方法。同时为了保证在其他网络环境下的效率，保留方法一所做的修改。
