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40 lines
1.6 KiB
40 lines
1.6 KiB
Replication Architecture
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========================
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Motivation
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----------
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We'd like to be able to split some of the work that synapse does into multiple
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python processes. In theory multiple synapse processes could share a single
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postgresql database and we'd scale up by running more synapse processes.
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However much of synapse assumes that only one process is interacting with the
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database, both for assigning unique identifiers when inserting into tables,
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notifying components about new updates, and for invalidating its caches.
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So running multiple copies of the current code isn't an option. One way to
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run multiple processes would be to have a single writer process and multiple
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reader processes connected to the same database. In order to do this we'd need
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a way for the reader process to invalidate its in-memory caches when an update
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happens on the writer. One way to do this is for the writer to present an
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append-only log of updates which the readers can consume to invalidate their
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caches and to push updates to listening clients or pushers.
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Synapse already stores much of its data as an append-only log so that it can
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correctly respond to /sync requests so the amount of code changes needed to
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expose the append-only log to the readers should be fairly minimal.
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Architecture
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------------
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The Replication Protocol
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~~~~~~~~~~~~~~~~~~~~~~~~
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See ``tcp_replication.rst``
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The Slaved DataStore
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~~~~~~~~~~~~~~~~~~~~
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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 replication
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API to invalidate their caches.
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