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The + Operator converting the given expression to a number +(new Date()) // 1593565210654 +true // 1 +false // 0 +"1e-8" // 100000000 +"1.6e-2" // 0.016 // overriding the valueOf() method of the random object const random = { 'valueOf': () => Math.floo...

Windows 11 右键单击系统托盘中的无线/网络图标。 选择 网络和 Internet 设置，然后在打开的页面中单击 VPN。 单击 添加 VPN 按钮。 从 VPN 提供商 下拉菜单选择 Windows (内置)。 在 连接名称 字段中输入任意内容。 在 服务器名称或地址 字段中输入你的 VPN 服务器 IP。 从 VPN 类型 下拉菜单选择 使用预共享密钥的 L2TP/IPsec。 在 预共享密钥 字段中输入你的 VPN IPsec PSK。 在 用户名 字段中输入你的 VPN 用户名...

Windows 错误 809 错误 809：无法建立计算机与 VPN 服务器之间的网络连接，因为远程服务器未响应。这可能是因为未将计算机与远程服务器之间的某种网络设备(如防火墙、NAT、路由器等)配置为允许 VPN 连接。请与管理员或服务提供商联系以确定哪种设备可能产生此问题。 注： 仅当你使用 IPsec/L2TP 模式连接到 VPN 时，才需要进行下面的注册表更改。对于 IKEv2 和 IPsec/XAuth 模式，不需要 进行此更改。 要解决此错误，在首次连接之前需要修改一次注册表，以解决 VP...

1. 进入手机设置页面 2. 添加一个VPN设置 3. 填写设置 4. 勾选一下刚添加的设置，点击上方连接，连接可能要花个几秒钟，连接成功后右上角会出现“VPN”标志

Functional Requirements what features must be included Non-Functional Requirements must be highly available and fast Example: Design a scalable, highly available, and fast messaging system Thought process we need to scale for writes and reads, ...

When writing a design document, we typically capture functional requirements in the form of use cases. Start from the end user, think about who they are and how are they going to use the system.

System uptime 99% availability => offline 3.65 days a year Request Success Ratio 99% availability => 1 failed request out of 100 Principles Behind High Availability Build redundancy to eliminate single points of failure regions, availability ...

Maintainability failure modes and mitigations if some component fails, what happens to the rest of the system? how the system handles network partitions? how we want the system to handle network partitions monitoring how do we monitor the health of...

Scale can be performed horizontally or vertically, it is important to compare the trade offs between them case by case. Horizontal scalling is not always the best choice. Elasticity the ability of a system to acquire resources as it needs them, and releas...

Performance is time required to process something (latency) rate at which something is processed (throughput) Response time = network delay + service time response time = client-side latency network delay = network latency service time = server-sid...

Requirements Clarification Users Who will use the system? How the system will be used? Scale How many read queries per second? How much data is queried per request? How many video views are processed per second? Can there be spikes in traffic...

High durability means low probability of data loss. Once data is successfully submitted to the system, it is not lost. How? By creating and maintaining multiple copies of data. Backups copy data from a non-volatile storage, such as disk, periodically 3 c...

Strong Consistency (changes are reflected to all users immeidately) vs Weak Consistency (changes take some time to reach all users because there're different versions of the data in the system) We need some terminologies in the middle: Consistency Models L...

Two primary asynchronous messaging models: Message queuing and Publish/subscribe. Competing Consumers Pattern multiple queue consumers fetching jobs from a queue, each job is processed once by one consumer Request/Response Messaging Pattern use a s...