233 lines
23 KiB
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233 lines
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<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="setup/forward_proxy.html">Configuring a Forward/Outbound 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="upgrade.html">Upgrading between Synapse 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href="deprecation_policy.html">Dependency Deprecation Policy</a></li><li class="chapter-item expanded "><a href="other/running_synapse_on_single_board_computers.html">Running Synapse on a Single-Board Computer</a></li></ol>
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<h1 id="replication-architecture"><a class="header" href="#replication-architecture">Replication Architecture</a></h1>
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<h2 id="motivation"><a class="header" href="#motivation">Motivation</a></h2>
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<p>We'd like to be able to split some of the work that synapse does into
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multiple python processes. In theory multiple synapse processes could
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share a single postgresql database and we'd scale up by running more
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synapse processes. However much of synapse assumes that only one process
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is interacting with the database, both for assigning unique identifiers
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when inserting into tables, notifying components about new updates, and
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for invalidating its caches.</p>
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<p>So running multiple copies of the current code isn't an option. One way
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to run multiple processes would be to have a single writer process and
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multiple reader processes connected to the same database. In order to do
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this we'd need a way for the reader process to invalidate its in-memory
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caches when an update happens on the writer. One way to do this is for
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the writer to present an append-only log of updates which the readers
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can consume to invalidate their caches and to push updates to listening
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clients or pushers.</p>
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<p>Synapse already stores much of its data as an append-only log so that it
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can correctly respond to <code>/sync</code> requests so the amount of code changes
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needed to expose the append-only log to the readers should be fairly
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minimal.</p>
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<h2 id="architecture"><a class="header" href="#architecture">Architecture</a></h2>
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<h3 id="the-replication-protocol"><a class="header" href="#the-replication-protocol">The Replication Protocol</a></h3>
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<p>See <a href="tcp_replication.html">the TCP replication documentation</a>.</p>
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<h3 id="the-slaved-datastore"><a class="header" href="#the-slaved-datastore">The Slaved DataStore</a></h3>
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<p>There are read-only version of the synapse storage layer in
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<code>synapse/replication/slave/storage</code> that use the response of the
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replication API to invalidate their caches.</p>
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