To make apt works the way I want, I add this file into /etc/apt/apt.conf.d/. Uses 99 prefix to override other apt.conf with lower prefix.

99local:

Acquire {
        Queue-Mode      "host";
        Retries         "990";
        http {
/*                Proxy           "http://127.0.0.1:3129"; */
                Timeout         "67";
                Pipeline-Depth  "5";
        };
};

APT {
        Default-Release "testing";

/*        Cache-Limit             "33554432"; */
        Periodic {
                Update-Package-Lists            "1";
                AutocleanInterval               "1";
                Download-Upgradeable-Packages   "0";
        };
        
        Archives {
                MinAge          "0";
                MaxAge          "0";
                MaxSize         "0";
        };
};

DPkg::Post-Invoke      { "if [ -x /usr/sbin/update-dlocatedb ]; then update-dlocatedb; fi"; };