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Replication Architecture

Motivation

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.

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.

Synapse already stores much of its data as an append-only log so that it +can correctly respond to /sync requests so the amount of code changes +needed to expose the append-only log to the readers should be fairly +minimal.

Synapse

Replication Architecture

Motivation

Architecture

The Replication Protocol

The TCP Replication Module