| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/tower-0.4.13/src/balance/p2c/mod.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>mod.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../../normalize.css"><link rel="stylesheet" href="../../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../../ayu.css" disabled><link rel="stylesheet" href="../../../../dark.css" disabled><link rel="stylesheet" href="../../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../../storage.js"></script><script defer src="../../../../source-script.js"></script><script defer src="../../../../source-files.js"></script><script defer src="../../../../main.js"></script><noscript><link rel="stylesheet" href="../../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../../tower/index.html"><div class="logo-container"><img class="rust-logo" src="../../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../../tower/index.html"><img class="rust-logo" src="../../../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="doccomment">//! This module implements the "[Power of Two Random Choices]" load balancing algorithm. |
| //! |
| //! It is a simple but robust technique for spreading load across services with only inexact load |
| //! measurements. As its name implies, whenever a request comes in, it samples two ready services |
| //! at random, and issues the request to whichever service is less loaded. How loaded a service is |
| //! is determined by the return value of [`Load`](crate::load::Load). |
| //! |
| //! As described in the [Finagle Guide][finagle]: |
| //! |
| //! > The algorithm randomly picks two services from the set of ready endpoints and |
| //! > selects the least loaded of the two. By repeatedly using this strategy, we can |
| //! > expect a manageable upper bound on the maximum load of any server. |
| //! > |
| //! > The maximum load variance between any two servers is bound by `ln(ln(n))` where |
| //! > `n` is the number of servers in the cluster. |
| //! |
| //! The balance service and layer implementations rely on _service discovery_ to provide the |
| //! underlying set of services to balance requests across. This happens through the |
| //! [`Discover`](crate::discover::Discover) trait, which is essentially a [`Stream`] that indicates |
| //! when services become available or go away. If you have a fixed set of services, consider using |
| //! [`ServiceList`](crate::discover::ServiceList). |
| //! |
| //! Since the load balancer needs to perform _random_ choices, the constructors in this module |
| //! usually come in two forms: one that uses randomness provided by the operating system, and one |
| //! that lets you specify the random seed to use. Usually the former is what you'll want, though |
| //! the latter may come in handy for reproducability or to reduce reliance on the operating system. |
| //! |
| //! [Power of Two Random Choices]: http://www.eecs.harvard.edu/~michaelm/postscripts/handbook2001.pdf |
| //! [finagle]: https://twitter.github.io/finagle/guide/Clients.html#power-of-two-choices-p2c-least-loaded |
| //! [`Stream`]: https://docs.rs/futures/0.3/futures/stream/trait.Stream.html |
| |
| </span><span class="kw">mod </span>layer; |
| <span class="kw">mod </span>make; |
| <span class="kw">mod </span>service; |
| |
| <span class="attribute">#[cfg(test)] |
| </span><span class="kw">mod </span>test; |
| |
| <span class="kw">pub use </span>layer::MakeBalanceLayer; |
| <span class="kw">pub use </span>make::{MakeBalance, MakeFuture}; |
| <span class="kw">pub use </span>service::Balance; |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../../" data-current-crate="tower" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
