replication.html 24 KB

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