mirror of
https://github.com/element-hq/synapse.git
synced 2024-12-18 17:10:43 +03:00
329 lines
18 KiB
HTML
329 lines
18 KiB
HTML
|
<!doctype html>
|
|||
|
<html class="no-js" lang="en">
|
|||
|
<head><meta charset="utf-8"/>
|
|||
|
<meta name="viewport" content="width=device-width,initial-scale=1"/>
|
|||
|
<meta name="color-scheme" content="light dark"><meta name="generator" content="Docutils 0.19: https://docutils.sourceforge.io/" />
|
|||
|
<link rel="index" title="Index" href="../genindex.html" /><link rel="search" title="Search" href="../search.html" /><link rel="prev" title="Welcome to the Synapse Developer Documentation!" href="../index.html" />
|
|||
|
|
|||
|
<!-- Generated with Sphinx 6.2.1 and Furo 2023.07.26 -->
|
|||
|
<title>Federation Sender - Synapse development documentation</title>
|
|||
|
<link rel="stylesheet" type="text/css" href="../_static/pygments.css" />
|
|||
|
<link rel="stylesheet" type="text/css" href="../_static/styles/furo.css?digest=369552022d0b975c8e74270ce6eabe0fb7978f24" />
|
|||
|
<link rel="stylesheet" type="text/css" href="../_static/styles/furo-extensions.css?digest=30d1aed668e5c3a91c3e3bf6a60b675221979f0e" />
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
<style>
|
|||
|
body {
|
|||
|
--color-code-background: #f8f8f8;
|
|||
|
--color-code-foreground: black;
|
|||
|
|
|||
|
}
|
|||
|
@media not print {
|
|||
|
body[data-theme="dark"] {
|
|||
|
--color-code-background: #202020;
|
|||
|
--color-code-foreground: #d0d0d0;
|
|||
|
|
|||
|
}
|
|||
|
@media (prefers-color-scheme: dark) {
|
|||
|
body:not([data-theme="light"]) {
|
|||
|
--color-code-background: #202020;
|
|||
|
--color-code-foreground: #d0d0d0;
|
|||
|
|
|||
|
}
|
|||
|
}
|
|||
|
}
|
|||
|
</style></head>
|
|||
|
<body>
|
|||
|
|
|||
|
<script>
|
|||
|
document.body.dataset.theme = localStorage.getItem("theme") || "auto";
|
|||
|
</script>
|
|||
|
|
|||
|
|
|||
|
<svg xmlns="http://www.w3.org/2000/svg" style="display: none;">
|
|||
|
<symbol id="svg-toc" viewBox="0 0 24 24">
|
|||
|
<title>Contents</title>
|
|||
|
<svg stroke="currentColor" fill="currentColor" stroke-width="0" viewBox="0 0 1024 1024">
|
|||
|
<path d="M408 442h480c4.4 0 8-3.6 8-8v-56c0-4.4-3.6-8-8-8H408c-4.4 0-8 3.6-8 8v56c0 4.4 3.6 8 8 8zm-8 204c0 4.4 3.6 8 8 8h480c4.4 0 8-3.6 8-8v-56c0-4.4-3.6-8-8-8H408c-4.4 0-8 3.6-8 8v56zm504-486H120c-4.4 0-8 3.6-8 8v56c0 4.4 3.6 8 8 8h784c4.4 0 8-3.6 8-8v-56c0-4.4-3.6-8-8-8zm0 632H120c-4.4 0-8 3.6-8 8v56c0 4.4 3.6 8 8 8h784c4.4 0 8-3.6 8-8v-56c0-4.4-3.6-8-8-8zM115.4 518.9L271.7 642c5.8 4.6 14.4.5 14.4-6.9V388.9c0-7.4-8.5-11.5-14.4-6.9L115.4 505.1a8.74 8.74 0 0 0 0 13.8z"/>
|
|||
|
</svg>
|
|||
|
</symbol>
|
|||
|
<symbol id="svg-menu" viewBox="0 0 24 24">
|
|||
|
<title>Menu</title>
|
|||
|
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor"
|
|||
|
stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather-menu">
|
|||
|
<line x1="3" y1="12" x2="21" y2="12"></line>
|
|||
|
<line x1="3" y1="6" x2="21" y2="6"></line>
|
|||
|
<line x1="3" y1="18" x2="21" y2="18"></line>
|
|||
|
</svg>
|
|||
|
</symbol>
|
|||
|
<symbol id="svg-arrow-right" viewBox="0 0 24 24">
|
|||
|
<title>Expand</title>
|
|||
|
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor"
|
|||
|
stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather-chevron-right">
|
|||
|
<polyline points="9 18 15 12 9 6"></polyline>
|
|||
|
</svg>
|
|||
|
</symbol>
|
|||
|
<symbol id="svg-sun" viewBox="0 0 24 24">
|
|||
|
<title>Light mode</title>
|
|||
|
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor"
|
|||
|
stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" class="feather-sun">
|
|||
|
<circle cx="12" cy="12" r="5"></circle>
|
|||
|
<line x1="12" y1="1" x2="12" y2="3"></line>
|
|||
|
<line x1="12" y1="21" x2="12" y2="23"></line>
|
|||
|
<line x1="4.22" y1="4.22" x2="5.64" y2="5.64"></line>
|
|||
|
<line x1="18.36" y1="18.36" x2="19.78" y2="19.78"></line>
|
|||
|
<line x1="1" y1="12" x2="3" y2="12"></line>
|
|||
|
<line x1="21" y1="12" x2="23" y2="12"></line>
|
|||
|
<line x1="4.22" y1="19.78" x2="5.64" y2="18.36"></line>
|
|||
|
<line x1="18.36" y1="5.64" x2="19.78" y2="4.22"></line>
|
|||
|
</svg>
|
|||
|
</symbol>
|
|||
|
<symbol id="svg-moon" viewBox="0 0 24 24">
|
|||
|
<title>Dark mode</title>
|
|||
|
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor"
|
|||
|
stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" class="icon-tabler-moon">
|
|||
|
<path stroke="none" d="M0 0h24v24H0z" fill="none" />
|
|||
|
<path d="M12 3c.132 0 .263 0 .393 0a7.5 7.5 0 0 0 7.92 12.446a9 9 0 1 1 -8.313 -12.454z" />
|
|||
|
</svg>
|
|||
|
</symbol>
|
|||
|
<symbol id="svg-sun-half" viewBox="0 0 24 24">
|
|||
|
<title>Auto light/dark mode</title>
|
|||
|
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor"
|
|||
|
stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" class="icon-tabler-shadow">
|
|||
|
<path stroke="none" d="M0 0h24v24H0z" fill="none"/>
|
|||
|
<circle cx="12" cy="12" r="9" />
|
|||
|
<path d="M13 12h5" />
|
|||
|
<path d="M13 15h4" />
|
|||
|
<path d="M13 18h1" />
|
|||
|
<path d="M13 9h4" />
|
|||
|
<path d="M13 6h1" />
|
|||
|
</svg>
|
|||
|
</symbol>
|
|||
|
</svg>
|
|||
|
|
|||
|
<input type="checkbox" class="sidebar-toggle" name="__navigation" id="__navigation">
|
|||
|
<input type="checkbox" class="sidebar-toggle" name="__toc" id="__toc">
|
|||
|
<label class="overlay sidebar-overlay" for="__navigation">
|
|||
|
<div class="visually-hidden">Hide navigation sidebar</div>
|
|||
|
</label>
|
|||
|
<label class="overlay toc-overlay" for="__toc">
|
|||
|
<div class="visually-hidden">Hide table of contents sidebar</div>
|
|||
|
</label>
|
|||
|
|
|||
|
|
|||
|
|
|||
|
<div class="page">
|
|||
|
<header class="mobile-header">
|
|||
|
<div class="header-left">
|
|||
|
<label class="nav-overlay-icon" for="__navigation">
|
|||
|
<div class="visually-hidden">Toggle site navigation sidebar</div>
|
|||
|
<i class="icon"><svg><use href="#svg-menu"></use></svg></i>
|
|||
|
</label>
|
|||
|
</div>
|
|||
|
<div class="header-center">
|
|||
|
<a href="../index.html"><div class="brand">Synapse development documentation</div></a>
|
|||
|
</div>
|
|||
|
<div class="header-right">
|
|||
|
<div class="theme-toggle-container theme-toggle-header">
|
|||
|
<button class="theme-toggle">
|
|||
|
<div class="visually-hidden">Toggle Light / Dark / Auto color theme</div>
|
|||
|
<svg class="theme-icon-when-auto"><use href="#svg-sun-half"></use></svg>
|
|||
|
<svg class="theme-icon-when-dark"><use href="#svg-moon"></use></svg>
|
|||
|
<svg class="theme-icon-when-light"><use href="#svg-sun"></use></svg>
|
|||
|
</button>
|
|||
|
</div>
|
|||
|
<label class="toc-overlay-icon toc-header-icon no-toc" for="__toc">
|
|||
|
<div class="visually-hidden">Toggle table of contents sidebar</div>
|
|||
|
<i class="icon"><svg><use href="#svg-toc"></use></svg></i>
|
|||
|
</label>
|
|||
|
</div>
|
|||
|
</header>
|
|||
|
<aside class="sidebar-drawer">
|
|||
|
<div class="sidebar-container">
|
|||
|
|
|||
|
<div class="sidebar-sticky"><a class="sidebar-brand" href="../index.html">
|
|||
|
|
|||
|
|
|||
|
<span class="sidebar-brand-text">Synapse development documentation</span>
|
|||
|
|
|||
|
</a><form class="sidebar-search-container" method="get" action="../search.html" role="search">
|
|||
|
<input class="sidebar-search" placeholder="Search" name="q" aria-label="Search">
|
|||
|
<input type="hidden" name="check_keywords" value="yes">
|
|||
|
<input type="hidden" name="area" value="default">
|
|||
|
</form>
|
|||
|
<div id="searchbox"></div><div class="sidebar-scroll"><div class="sidebar-tree">
|
|||
|
<p class="caption" role="heading"><span class="caption-text">Contents:</span></p>
|
|||
|
<ul class="current">
|
|||
|
<li class="toctree-l1 current current-page"><a class="current reference internal" href="#">Federation Sender</a></li>
|
|||
|
</ul>
|
|||
|
|
|||
|
</div>
|
|||
|
</div>
|
|||
|
|
|||
|
</div>
|
|||
|
|
|||
|
</div>
|
|||
|
</aside>
|
|||
|
<div class="main">
|
|||
|
<div class="content">
|
|||
|
<div class="article-container">
|
|||
|
<a href="#" class="back-to-top muted-link">
|
|||
|
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
|
|||
|
<path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8v12z"></path>
|
|||
|
</svg>
|
|||
|
<span>Back to top</span>
|
|||
|
</a>
|
|||
|
<div class="content-icon-container">
|
|||
|
|
|||
|
<div class="theme-toggle-container theme-toggle-content">
|
|||
|
<button class="theme-toggle">
|
|||
|
<div class="visually-hidden">Toggle Light / Dark / Auto color theme</div>
|
|||
|
<svg class="theme-icon-when-auto"><use href="#svg-sun-half"></use></svg>
|
|||
|
<svg class="theme-icon-when-dark"><use href="#svg-moon"></use></svg>
|
|||
|
<svg class="theme-icon-when-light"><use href="#svg-sun"></use></svg>
|
|||
|
</button>
|
|||
|
</div>
|
|||
|
<label class="toc-overlay-icon toc-content-icon no-toc" for="__toc">
|
|||
|
<div class="visually-hidden">Toggle table of contents sidebar</div>
|
|||
|
<i class="icon"><svg><use href="#svg-toc"></use></svg></i>
|
|||
|
</label>
|
|||
|
</div>
|
|||
|
<article role="main">
|
|||
|
<section id="federation-sender">
|
|||
|
<h1>Federation Sender<a class="headerlink" href="#federation-sender" title="Permalink to this heading">#</a></h1>
|
|||
|
<p>The Federation Sender is responsible for sending Persistent Data Units (PDUs)
|
|||
|
and Ephemeral Data Units (EDUs) to other homeservers using
|
|||
|
the <code class="docutils literal notranslate"><span class="pre">/send</span></code> Federation API.</p>
|
|||
|
<h2 class="rubric" id="how-do-pdus-get-sent">How do PDUs get sent?</h2>
|
|||
|
<p>The Federation Sender is made aware of new PDUs due to <code class="docutils literal notranslate"><span class="pre">FederationSender.notify_new_events</span></code>.
|
|||
|
When the sender is notified about a newly-persisted PDU that originates from this homeserver
|
|||
|
and is not an out-of-band event, we pass the PDU to the <code class="docutils literal notranslate"><span class="pre">_PerDestinationQueue</span></code> for each
|
|||
|
remote homeserver that is in the room at that point in the DAG.</p>
|
|||
|
<h3 class="rubric" id="per-destination-queues">Per-Destination Queues</h3>
|
|||
|
<p>There is one <code class="docutils literal notranslate"><span class="pre">PerDestinationQueue</span></code> per ‘destination’ homeserver.
|
|||
|
The <code class="docutils literal notranslate"><span class="pre">PerDestinationQueue</span></code> maintains the following information about the destination:</p>
|
|||
|
<ul class="simple">
|
|||
|
<li><p>whether the destination is currently in <a class="reference internal" href="#catch-up-mode"><span class="xref myst">catch-up mode (see below)</span></a>;</p></li>
|
|||
|
<li><p>a queue of PDUs to be sent to the destination; and</p></li>
|
|||
|
<li><p>a queue of EDUs to be sent to the destination (not considered in this section).</p></li>
|
|||
|
</ul>
|
|||
|
<p>Upon a new PDU being enqueued, <code class="docutils literal notranslate"><span class="pre">attempt_new_transaction</span></code> is called to start a new
|
|||
|
transaction if there is not already one in progress.</p>
|
|||
|
<h3 class="rubric" id="transactions-and-the-transaction-transmission-loop">Transactions and the Transaction Transmission Loop</h3>
|
|||
|
<p>Each federation HTTP request to the <code class="docutils literal notranslate"><span class="pre">/send</span></code> endpoint is referred to as a ‘transaction’.
|
|||
|
The body of the HTTP request contains a list of PDUs and EDUs to send to the destination.</p>
|
|||
|
<p>The <em>Transaction Transmission Loop</em> (<code class="docutils literal notranslate"><span class="pre">_transaction_transmission_loop</span></code>) is responsible
|
|||
|
for emptying the queued PDUs (and EDUs) from a <code class="docutils literal notranslate"><span class="pre">PerDestinationQueue</span></code> by sending
|
|||
|
them to the destination.</p>
|
|||
|
<p>There can only be one transaction in flight for a given destination at any time.
|
|||
|
(Other than preventing us from overloading the destination, this also makes it easier to
|
|||
|
reason about because we process events sequentially for each destination.
|
|||
|
This is useful for <em>Catch-Up Mode</em>, described later.)</p>
|
|||
|
<p>The loop continues so long as there is anything to send. At each iteration of the loop, we:</p>
|
|||
|
<ul class="simple">
|
|||
|
<li><p>dequeue up to 50 PDUs (and up to 100 EDUs).</p></li>
|
|||
|
<li><p>make the <code class="docutils literal notranslate"><span class="pre">/send</span></code> request to the destination homeserver with the dequeued PDUs and EDUs.</p></li>
|
|||
|
<li><p>if successful, make note of the fact that we succeeded in transmitting PDUs up to
|
|||
|
the given <code class="docutils literal notranslate"><span class="pre">stream_ordering</span></code> of the latest PDU by</p></li>
|
|||
|
<li><p>if unsuccessful, back off from the remote homeserver for some time.
|
|||
|
If we have been unsuccessful for too long (when the backoff interval grows to exceed 1 hour),
|
|||
|
the in-memory queues are emptied and we enter <a class="reference internal" href="#catch-up-mode"><span class="xref myst"><em>Catch-Up Mode</em>, described below</span></a>.</p></li>
|
|||
|
</ul>
|
|||
|
<h3 class="rubric" id="catch-up-mode">Catch-Up Mode</h3>
|
|||
|
<p>When the <code class="docutils literal notranslate"><span class="pre">PerDestinationQueue</span></code> has the catch-up flag set, the <em>Catch-Up Transmission Loop</em>
|
|||
|
(<code class="docutils literal notranslate"><span class="pre">_catch_up_transmission_loop</span></code>) is used in lieu of the regular <code class="docutils literal notranslate"><span class="pre">_transaction_transmission_loop</span></code>.
|
|||
|
(Only once the catch-up mode has been exited can the regular tranaction transmission behaviour
|
|||
|
be resumed.)</p>
|
|||
|
<p><em>Catch-Up Mode</em>, entered upon Synapse startup or once a homeserver has fallen behind due to
|
|||
|
connection problems, is responsible for sending PDUs that have been missed by the destination
|
|||
|
homeserver. (PDUs can be missed because the <code class="docutils literal notranslate"><span class="pre">PerDestinationQueue</span></code> is volatile — i.e. resets
|
|||
|
on startup — and it does not hold PDUs forever if <code class="docutils literal notranslate"><span class="pre">/send</span></code> requests to the destination fail.)</p>
|
|||
|
<p>The catch-up mechanism makes use of the <code class="docutils literal notranslate"><span class="pre">last_successful_stream_ordering</span></code> column in the
|
|||
|
<code class="docutils literal notranslate"><span class="pre">destinations</span></code> table (which gives the <code class="docutils literal notranslate"><span class="pre">stream_ordering</span></code> of the most recent successfully
|
|||
|
sent PDU) and the <code class="docutils literal notranslate"><span class="pre">stream_ordering</span></code> column in the <code class="docutils literal notranslate"><span class="pre">destination_rooms</span></code> table (which gives,
|
|||
|
for each room, the <code class="docutils literal notranslate"><span class="pre">stream_ordering</span></code> of the most recent PDU that needs to be sent to this
|
|||
|
destination).</p>
|
|||
|
<p>Each iteration of the loop pulls out 50 <code class="docutils literal notranslate"><span class="pre">destination_rooms</span></code> entries with the oldest
|
|||
|
<code class="docutils literal notranslate"><span class="pre">stream_ordering</span></code>s that are greater than the <code class="docutils literal notranslate"><span class="pre">last_successful_stream_ordering</span></code>.
|
|||
|
In other words, from the set of latest PDUs in each room to be sent to the destination,
|
|||
|
the 50 oldest such PDUs are pulled out.</p>
|
|||
|
<p>These PDUs could, in principle, now be directly sent to the destination. However, as an
|
|||
|
optimisation intended to prevent overloading destination homeservers, we instead attempt
|
|||
|
to send the latest forward extremities so long as the destination homeserver is still
|
|||
|
eligible to receive those.
|
|||
|
This reduces load on the destination <strong>in aggregate</strong> because all Synapse homeservers
|
|||
|
will behave according to this principle and therefore avoid sending lots of different PDUs
|
|||
|
at different points in the DAG to a recovering homeserver.
|
|||
|
<em>This optimisation is not currently valid in rooms which are partial-state on this homeserver,
|
|||
|
since we are unable to determine whether the destination homeserver is eligible to receive
|
|||
|
the latest forward extremities unless this homeserver sent those PDUs — in this case, we
|
|||
|
just send the latest PDUs originating from this server and skip this optimisation.</em></p>
|
|||
|
<p>Whilst PDUs are sent through this mechanism, the position of <code class="docutils literal notranslate"><span class="pre">last_successful_stream_ordering</span></code>
|
|||
|
is advanced as normal.
|
|||
|
Once there are no longer any rooms containing outstanding PDUs to be sent to the destination
|
|||
|
<em>that are not already in the <code class="docutils literal notranslate"><span class="pre">PerDestinationQueue</span></code> because they arrived since Catch-Up Mode
|
|||
|
was enabled</em>, Catch-Up Mode is exited and we return to <code class="docutils literal notranslate"><span class="pre">_transaction_transmission_loop</span></code>.</p>
|
|||
|
<h4 class="rubric" id="a-note-on-failures-and-back-offs">A note on failures and back-offs</h4>
|
|||
|
<p>If a remote server is unreachable over federation, we back off from that server,
|
|||
|
with an exponentially-increasing retry interval.
|
|||
|
We automatically retry after the retry interval expires (roughly, the logic to do so
|
|||
|
being triggered every minute).</p>
|
|||
|
<p>If the backoff grows too large (> 1 hour), the in-memory queue is emptied (to prevent
|
|||
|
unbounded growth) and Catch-Up Mode is entered.</p>
|
|||
|
<p>It is worth noting that the back-off for a remote server is cleared once an inbound
|
|||
|
request from that remote server is received (see <code class="docutils literal notranslate"><span class="pre">notify_remote_server_up</span></code>).
|
|||
|
At this point, the transaction transmission loop is also started up, to proactively
|
|||
|
send missed PDUs and EDUs to the destination (i.e. you don’t need to wait for a new PDU
|
|||
|
or EDU, destined for that destination, to be created in order to send out missed PDUs and
|
|||
|
EDUs).</p>
|
|||
|
</section>
|
|||
|
|
|||
|
</article>
|
|||
|
</div>
|
|||
|
<footer>
|
|||
|
|
|||
|
<div class="related-pages">
|
|||
|
|
|||
|
<a class="prev-page" href="../index.html">
|
|||
|
<svg class="furo-related-icon"><use href="#svg-arrow-right"></use></svg>
|
|||
|
<div class="page-info">
|
|||
|
<div class="context">
|
|||
|
<span>Previous</span>
|
|||
|
</div>
|
|||
|
|
|||
|
<div class="title">Home</div>
|
|||
|
|
|||
|
</div>
|
|||
|
</a>
|
|||
|
</div>
|
|||
|
<div class="bottom-of-page">
|
|||
|
<div class="left-details">
|
|||
|
<div class="copyright">
|
|||
|
Copyright © 2023, The Matrix.org Foundation C.I.C.
|
|||
|
</div>
|
|||
|
Made with <a href="https://www.sphinx-doc.org/">Sphinx</a> and <a class="muted-link" href="https://pradyunsg.me">@pradyunsg</a>'s
|
|||
|
|
|||
|
<a href="https://github.com/pradyunsg/furo">Furo</a>
|
|||
|
|
|||
|
</div>
|
|||
|
<div class="right-details">
|
|||
|
|
|||
|
</div>
|
|||
|
</div>
|
|||
|
|
|||
|
</footer>
|
|||
|
</div>
|
|||
|
<aside class="toc-drawer no-toc">
|
|||
|
|
|||
|
|
|||
|
|
|||
|
</aside>
|
|||
|
</div>
|
|||
|
</div><script data-url_root="../" id="documentation_options" src="../_static/documentation_options.js"></script>
|
|||
|
<script src="../_static/doctools.js"></script>
|
|||
|
<script src="../_static/sphinx_highlight.js"></script>
|
|||
|
<script src="../_static/scripts/furo.js"></script>
|
|||
|
</body>
|
|||
|
</html>
|