346 lines
24 KiB
HTML
346 lines
24 KiB
HTML
<!DOCTYPE HTML>
|
|
<html lang="en" class="sidebar-visible no-js light">
|
|
<head>
|
|
<!-- Book generated using mdBook -->
|
|
<meta charset="UTF-8">
|
|
<title>The Auth Chain Difference Algorithm - Synapse</title>
|
|
|
|
|
|
|
|
|
|
<!-- Custom HTML head -->
|
|
|
|
|
|
|
|
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
|
|
<meta name="description" content="">
|
|
<meta name="viewport" content="width=device-width, initial-scale=1">
|
|
<meta name="theme-color" content="#ffffff" />
|
|
|
|
|
|
<link rel="icon" href="favicon.svg">
|
|
|
|
|
|
<link rel="shortcut icon" href="favicon.png">
|
|
|
|
<link rel="stylesheet" href="css/variables.css">
|
|
<link rel="stylesheet" href="css/general.css">
|
|
<link rel="stylesheet" href="css/chrome.css">
|
|
|
|
<link rel="stylesheet" href="css/print.css" media="print">
|
|
|
|
|
|
<!-- Fonts -->
|
|
<link rel="stylesheet" href="FontAwesome/css/font-awesome.css">
|
|
|
|
<link rel="stylesheet" href="fonts/fonts.css">
|
|
|
|
|
|
<!-- Highlight.js Stylesheets -->
|
|
<link rel="stylesheet" href="highlight.css">
|
|
<link rel="stylesheet" href="tomorrow-night.css">
|
|
<link rel="stylesheet" href="ayu-highlight.css">
|
|
|
|
<!-- Custom theme stylesheets -->
|
|
|
|
<link rel="stylesheet" href="docs/website_files/table-of-contents.css">
|
|
|
|
<link rel="stylesheet" href="docs/website_files/remove-nav-buttons.css">
|
|
|
|
<link rel="stylesheet" href="docs/website_files/indent-section-headers.css">
|
|
|
|
|
|
|
|
</head>
|
|
<body>
|
|
<!-- Provide site root to javascript -->
|
|
<script type="text/javascript">
|
|
var path_to_root = "";
|
|
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
|
|
</script>
|
|
|
|
<!-- Work around some values being stored in localStorage wrapped in quotes -->
|
|
<script type="text/javascript">
|
|
try {
|
|
var theme = localStorage.getItem('mdbook-theme');
|
|
var sidebar = localStorage.getItem('mdbook-sidebar');
|
|
if (theme.startsWith('"') && theme.endsWith('"')) {
|
|
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
|
|
}
|
|
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
|
|
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
|
|
}
|
|
} catch (e) { }
|
|
</script>
|
|
|
|
<!-- Set the theme before any content is loaded, prevents flash -->
|
|
<script type="text/javascript">
|
|
var theme;
|
|
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
|
|
if (theme === null || theme === undefined) { theme = default_theme; }
|
|
var html = document.querySelector('html');
|
|
html.classList.remove('no-js')
|
|
html.classList.remove('light')
|
|
html.classList.add(theme);
|
|
html.classList.add('js');
|
|
</script>
|
|
|
|
<!-- Hide / unhide sidebar before it is displayed -->
|
|
<script type="text/javascript">
|
|
var html = document.querySelector('html');
|
|
var sidebar = 'hidden';
|
|
if (document.body.clientWidth >= 1080) {
|
|
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
|
|
sidebar = sidebar || 'visible';
|
|
}
|
|
html.classList.remove('sidebar-visible');
|
|
html.classList.add("sidebar-" + sidebar);
|
|
</script>
|
|
|
|
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
|
|
<div class="sidebar-scrollbox">
|
|
<ol class="chapter"><li class="chapter-item expanded affix "><li class="part-title">Introduction</li><li class="chapter-item expanded "><a href="welcome_and_overview.html">Welcome and Overview</a></li><li class="chapter-item expanded affix "><li class="part-title">Setup</li><li class="chapter-item expanded "><a href="setup/installation.html">Installation</a></li><li class="chapter-item expanded "><a href="postgres.html">Using Postgres</a></li><li class="chapter-item expanded "><a href="reverse_proxy.html">Configuring a Reverse Proxy</a></li><li class="chapter-item expanded "><a href="turn-howto.html">Configuring a Turn Server</a></li><li class="chapter-item expanded "><a href="delegate.html">Delegation</a></li><li class="chapter-item expanded affix "><li class="part-title">Upgrading</li><li class="chapter-item expanded "><a href="upgrading/index.html">Upgrading between Synapse Versions</a></li><li class="chapter-item expanded "><a href="MSC1711_certificates_FAQ.html">Upgrading from pre-Synapse 1.0</a></li><li class="chapter-item expanded affix "><li class="part-title">Usage</li><li class="chapter-item expanded "><a href="federate.html">Federation</a></li><li class="chapter-item expanded "><a href="usage/configuration/index.html">Configuration</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="usage/configuration/homeserver_sample_config.html">Homeserver Sample Config File</a></li><li class="chapter-item expanded "><a href="usage/configuration/logging_sample_config.html">Logging Sample Config File</a></li><li class="chapter-item expanded "><a href="structured_logging.html">Structured Logging</a></li><li class="chapter-item expanded "><a href="usage/configuration/user_authentication/index.html">User Authentication</a></li><li><ol class="section"><li class="chapter-item expanded "><div>Single-Sign On</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="openid.html">OpenID Connect</a></li><li class="chapter-item expanded "><div>SAML</div></li><li class="chapter-item expanded "><div>CAS</div></li><li class="chapter-item expanded "><a href="sso_mapping_providers.html">SSO Mapping Providers</a></li></ol></li><li class="chapter-item expanded "><a href="password_auth_providers.html">Password Auth Providers</a></li><li class="chapter-item expanded "><a href="jwt.html">JSON Web Tokens</a></li></ol></li><li class="chapter-item expanded "><a href="CAPTCHA_SETUP.html">Registration Captcha</a></li><li class="chapter-item expanded "><a href="application_services.html">Application Services</a></li><li class="chapter-item expanded "><a href="server_notices.html">Server Notices</a></li><li class="chapter-item expanded "><a href="consent_tracking.html">Consent Tracking</a></li><li class="chapter-item expanded "><a href="url_previews.html">URL Previews</a></li><li class="chapter-item expanded "><a href="user_directory.html">User Directory</a></li><li class="chapter-item expanded "><a href="message_retention_policies.html">Message Retention Policies</a></li><li class="chapter-item expanded "><div>Pluggable Modules</div></li><li><ol class="section"><li class="chapter-item expanded "><div>Third Party Rules</div></li><li class="chapter-item expanded "><a href="spam_checker.html">Spam Checker</a></li><li class="chapter-item expanded "><a href="presence_router_module.html">Presence Router</a></li><li class="chapter-item expanded "><div>Media Storage Providers</div></li></ol></li><li class="chapter-item expanded "><a href="workers.html">Workers</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="synctl_workers.html">Using synctl with Workers</a></li><li class="chapter-item expanded "><a href="systemd-with-workers/index.html">Systemd</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="usage/administration/index.html">Administration</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="usage/administration/admin_api/index.html">Admin API</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="admin_api/account_validity.html">Account Validity</a></li><li class="chapter-item expanded "><a href="admin_api/delete_group.html">Delete Group</a></li><li class="chapter-item expanded "><a href="admin_api/event_reports.html">Event Reports</a></li><li class="chapter-item expanded "><a href="admin_api/media_admin_api.html">Media</a></li><li class="chapter-item expanded "><a href="admin_api/purge_history_api.html">Purge History</a></li><li class="chapter-item expanded "><a href="admin_api/purge_room.html">Purge Rooms</a></li><li class="chapter-item expanded "><a href="admin_api/register_api.html">Register Users</a></li><li class="chapter-item expanded "><a href="admin_api/room_membership.html">Manipulate Room Membership</a></li><li class="chapter-item expanded "><a href="admin_api/rooms.html">Rooms</a></li><li class="chapter-item expanded "><a href="admin_api/server_notices.html">Server Notices</a></li><li class="chapter-item expanded "><a href="admin_api/shutdown_room.html">Shutdown Room</a></li><li class="chapter-item expanded "><a href="admin_api/statistics.html">Statistics</a></li><li class="chapter-item expanded "><a href="admin_api/user_admin_api.html">Users</a></li><li class="chapter-item expanded "><a href="admin_api/version_api.html">Server Version</a></li></ol></li><li class="chapter-item expanded "><a href="manhole.html">Manhole</a></li><li class="chapter-item expanded "><a href="metrics-howto.html">Monitoring</a></li><li class="chapter-item expanded "><div>Scripts</div></li></ol></li><li class="chapter-item expanded "><li class="part-title">Development</li><li class="chapter-item expanded "><a href="development/contributing_guide.html">Contributing Guide</a></li><li class="chapter-item expanded "><a href="code_style.html">Code Style</a></li><li class="chapter-item expanded "><a href="dev/git.html">Git Usage</a></li><li class="chapter-item expanded "><div>Testing</div></li><li class="chapter-item expanded "><a href="opentracing.html">OpenTracing</a></li><li class="chapter-item expanded "><div>Synapse Architecture</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="log_contexts.html">Log Contexts</a></li><li class="chapter-item expanded "><a href="replication.html">Replication</a></li><li class="chapter-item expanded "><a href="tcp_replication.html">TCP Replication</a></li></ol></li><li class="chapter-item expanded "><a href="development/internal_documentation/index.html">Internal Documentation</a></li><li><ol class="section"><li class="chapter-item expanded "><div>Single Sign-On</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="dev/saml.html">SAML</a></li><li class="chapter-item expanded "><a href="dev/cas.html">CAS</a></li></ol></li><li class="chapter-item expanded "><div>State Resolution</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="auth_chain_difference_algorithm.html" class="active">The Auth Chain Difference Algorithm</a></li></ol></li><li class="chapter-item expanded "><a href="media_repository.html">Media Repository</a></li><li class="chapter-item expanded "><a href="room_and_user_statistics.html">Room and User Statistics</a></li></ol></li><li class="chapter-item expanded "><div>Scripts</div></li><li class="chapter-item expanded affix "><li class="part-title">Other</li><li class="chapter-item expanded "><a href="deprecation_policy.html">Dependency Deprecation Policy</a></li></ol>
|
|
</div>
|
|
<div id="sidebar-resize-handle" class="sidebar-resize-handle"></div>
|
|
</nav>
|
|
|
|
<div id="page-wrapper" class="page-wrapper">
|
|
|
|
<div class="page">
|
|
|
|
<div id="menu-bar-hover-placeholder"></div>
|
|
<div id="menu-bar" class="menu-bar sticky bordered">
|
|
<div class="left-buttons">
|
|
<button id="sidebar-toggle" class="icon-button" type="button" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
|
|
<i class="fa fa-bars"></i>
|
|
</button>
|
|
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
|
|
<i class="fa fa-paint-brush"></i>
|
|
</button>
|
|
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
|
|
<li role="none"><button role="menuitem" class="theme" id="light">Light (default)</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
|
|
</ul>
|
|
|
|
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
|
|
<i class="fa fa-search"></i>
|
|
</button>
|
|
|
|
</div>
|
|
|
|
<h1 class="menu-title">Synapse</h1>
|
|
|
|
<div class="right-buttons">
|
|
|
|
<a href="print.html" title="Print this book" aria-label="Print this book">
|
|
<i id="print-button" class="fa fa-print"></i>
|
|
</a>
|
|
|
|
|
|
<a href="https://github.com/matrix-org/synapse" title="Git repository" aria-label="Git repository">
|
|
<i id="git-repository-button" class="fa fa-github"></i>
|
|
</a>
|
|
|
|
|
|
<a href="https://github.com/matrix-org/synapse/edit/develop/docs/auth_chain_difference_algorithm.md" title="Suggest an edit" aria-label="Suggest an edit">
|
|
<i id="git-edit-button" class="fa fa-edit"></i>
|
|
</a>
|
|
|
|
|
|
</div>
|
|
</div>
|
|
|
|
|
|
<div id="search-wrapper" class="hidden">
|
|
<form id="searchbar-outer" class="searchbar-outer">
|
|
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
|
|
</form>
|
|
<div id="searchresults-outer" class="searchresults-outer hidden">
|
|
<div id="searchresults-header" class="searchresults-header"></div>
|
|
<ul id="searchresults">
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
|
|
|
|
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
|
|
<script type="text/javascript">
|
|
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
|
|
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
|
|
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
|
|
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
|
|
});
|
|
</script>
|
|
|
|
<div id="content" class="content">
|
|
<main>
|
|
<!-- Page table of contents -->
|
|
<div class="sidetoc">
|
|
<nav class="pagetoc"></nav>
|
|
</div>
|
|
|
|
<h1 id="auth-chain-difference-algorithm"><a class="header" href="#auth-chain-difference-algorithm">Auth Chain Difference Algorithm</a></h1>
|
|
<p>The auth chain difference algorithm is used by V2 state resolution, where a
|
|
naive implementation can be a significant source of CPU and DB usage.</p>
|
|
<h3 id="definitions"><a class="header" href="#definitions">Definitions</a></h3>
|
|
<p>A <em>state set</em> is a set of state events; e.g. the input of a state resolution
|
|
algorithm is a collection of state sets.</p>
|
|
<p>The <em>auth chain</em> of a set of events are all the events' auth events and <em>their</em>
|
|
auth events, recursively (i.e. the events reachable by walking the graph induced
|
|
by an event's auth events links).</p>
|
|
<p>The <em>auth chain difference</em> of a collection of state sets is the union minus the
|
|
intersection of the sets of auth chains corresponding to the state sets, i.e an
|
|
event is in the auth chain difference if it is reachable by walking the auth
|
|
event graph from at least one of the state sets but not from <em>all</em> of the state
|
|
sets.</p>
|
|
<h2 id="breadth-first-walk-algorithm"><a class="header" href="#breadth-first-walk-algorithm">Breadth First Walk Algorithm</a></h2>
|
|
<p>A way of calculating the auth chain difference without calculating the full auth
|
|
chains for each state set is to do a parallel breadth first walk (ordered by
|
|
depth) of each state set's auth chain. By tracking which events are reachable
|
|
from each state set we can finish early if every pending event is reachable from
|
|
every state set.</p>
|
|
<p>This can work well for state sets that have a small auth chain difference, but
|
|
can be very inefficient for larger differences. However, this algorithm is still
|
|
used if we don't have a chain cover index for the room (e.g. because we're in
|
|
the process of indexing it).</p>
|
|
<h2 id="chain-cover-index"><a class="header" href="#chain-cover-index">Chain Cover Index</a></h2>
|
|
<p>Synapse computes auth chain differences by pre-computing a "chain cover" index
|
|
for the auth chain in a room, allowing efficient reachability queries like "is
|
|
event A in the auth chain of event B". This is done by assigning every event a
|
|
<em>chain ID</em> and <em>sequence number</em> (e.g. <code>(5,3)</code>), and having a map of <em>links</em>
|
|
between chains (e.g. <code>(5,3) -> (2,4)</code>) such that A is reachable by B (i.e. <code>A</code>
|
|
is in the auth chain of <code>B</code>) if and only if either:</p>
|
|
<ol>
|
|
<li>A and B have the same chain ID and <code>A</code>'s sequence number is less than <code>B</code>'s
|
|
sequence number; or</li>
|
|
<li>there is a link <code>L</code> between <code>B</code>'s chain ID and <code>A</code>'s chain ID such that
|
|
<code>L.start_seq_no</code> <= <code>B.seq_no</code> and <code>A.seq_no</code> <= <code>L.end_seq_no</code>.</li>
|
|
</ol>
|
|
<p>There are actually two potential implementations, one where we store links from
|
|
each chain to every other reachable chain (the transitive closure of the links
|
|
graph), and one where we remove redundant links (the transitive reduction of the
|
|
links graph) e.g. if we have chains <code>C3 -> C2 -> C1</code> then the link <code>C3 -> C1</code>
|
|
would not be stored. Synapse uses the former implementations so that it doesn't
|
|
need to recurse to test reachability between chains.</p>
|
|
<h3 id="example"><a class="header" href="#example">Example</a></h3>
|
|
<p>An example auth graph would look like the following, where chains have been
|
|
formed based on type/state_key and are denoted by colour and are labelled with
|
|
<code>(chain ID, sequence number)</code>. Links are denoted by the arrows (links in grey
|
|
are those that would be remove in the second implementation described above).</p>
|
|
<p><img src="auth_chain_diff.dot.png" alt="Example" /></p>
|
|
<p>Note that we don't include all links between events and their auth events, as
|
|
most of those links would be redundant. For example, all events point to the
|
|
create event, but each chain only needs the one link from it's base to the
|
|
create event.</p>
|
|
<h2 id="using-the-index"><a class="header" href="#using-the-index">Using the Index</a></h2>
|
|
<p>This index can be used to calculate the auth chain difference of the state sets
|
|
by looking at the chain ID and sequence numbers reachable from each state set:</p>
|
|
<ol>
|
|
<li>For every state set lookup the chain ID/sequence numbers of each state event</li>
|
|
<li>Use the index to find all chains and the maximum sequence number reachable
|
|
from each state set.</li>
|
|
<li>The auth chain difference is then all events in each chain that have sequence
|
|
numbers between the maximum sequence number reachable from <em>any</em> state set and
|
|
the minimum reachable by <em>all</em> state sets (if any).</li>
|
|
</ol>
|
|
<p>Note that steps 2 is effectively calculating the auth chain for each state set
|
|
(in terms of chain IDs and sequence numbers), and step 3 is calculating the
|
|
difference between the union and intersection of the auth chains.</p>
|
|
<h3 id="worked-example"><a class="header" href="#worked-example">Worked Example</a></h3>
|
|
<p>For example, given the above graph, we can calculate the difference between
|
|
state sets consisting of:</p>
|
|
<ol>
|
|
<li><code>S1</code>: Alice's invite <code>(4,1)</code> and Bob's second join <code>(2,2)</code>; and</li>
|
|
<li><code>S2</code>: Alice's second join <code>(4,3)</code> and Bob's first join <code>(2,1)</code>.</li>
|
|
</ol>
|
|
<p>Using the index we see that the following auth chains are reachable from each
|
|
state set:</p>
|
|
<ol>
|
|
<li><code>S1</code>: <code>(1,1)</code>, <code>(2,2)</code>, <code>(3,1)</code> & <code>(4,1)</code></li>
|
|
<li><code>S2</code>: <code>(1,1)</code>, <code>(2,1)</code>, <code>(3,2)</code> & <code>(4,3)</code></li>
|
|
</ol>
|
|
<p>And so, for each the ranges that are in the auth chain difference:</p>
|
|
<ol>
|
|
<li>Chain 1: None, (since everything can reach the create event).</li>
|
|
<li>Chain 2: The range <code>(1, 2]</code> (i.e. just <code>2</code>), as <code>1</code> is reachable by all state
|
|
sets and the maximum reachable is <code>2</code> (corresponding to Bob's second join).</li>
|
|
<li>Chain 3: Similarly the range <code>(1, 2]</code> (corresponding to the second power
|
|
level).</li>
|
|
<li>Chain 4: The range <code>(1, 3]</code> (corresponding to both of Alice's joins).</li>
|
|
</ol>
|
|
<p>So the final result is: Bob's second join <code>(2,2)</code>, the second power level
|
|
<code>(3,2)</code> and both of Alice's joins <code>(4,2)</code> & <code>(4,3)</code>.</p>
|
|
|
|
</main>
|
|
|
|
<nav class="nav-wrapper" aria-label="Page navigation">
|
|
<!-- Mobile navigation buttons -->
|
|
|
|
<a rel="prev" href="dev/cas.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
<i class="fa fa-angle-left"></i>
|
|
</a>
|
|
|
|
|
|
|
|
<a rel="next" href="media_repository.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|
<i class="fa fa-angle-right"></i>
|
|
</a>
|
|
|
|
|
|
<div style="clear: both"></div>
|
|
</nav>
|
|
</div>
|
|
</div>
|
|
|
|
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
|
|
|
<a rel="prev" href="dev/cas.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
<i class="fa fa-angle-left"></i>
|
|
</a>
|
|
|
|
|
|
|
|
<a rel="next" href="media_repository.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|
<i class="fa fa-angle-right"></i>
|
|
</a>
|
|
|
|
</nav>
|
|
|
|
</div>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<script type="text/javascript">
|
|
window.playground_copyable = true;
|
|
</script>
|
|
|
|
|
|
|
|
|
|
|
|
<script src="elasticlunr.min.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="mark.min.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="searcher.js" type="text/javascript" charset="utf-8"></script>
|
|
|
|
|
|
<script src="clipboard.min.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="highlight.js" type="text/javascript" charset="utf-8"></script>
|
|
<script src="book.js" type="text/javascript" charset="utf-8"></script>
|
|
|
|
<!-- Custom JS scripts -->
|
|
|
|
<script type="text/javascript" src="docs/website_files/table-of-contents.js"></script>
|
|
|
|
|
|
|
|
|
|
</body>
|
|
</html> |