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38 lines
1.5 KiB
Markdown
38 lines
1.5 KiB
Markdown
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# Replication Architecture
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## Motivation
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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.
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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.
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Synapse already stores much of its data as an append-only log so that it
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can correctly respond to `/sync` 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.
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## Architecture
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### The Replication Protocol
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See [tcp_replication.md](tcp_replication.md)
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### The Slaved DataStore
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There are read-only version of the synapse storage layer in
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`synapse/replication/slave/storage` that use the response of the
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replication API to invalidate their caches.
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