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