Add support for importing an existing Postgres database

docs/importing-postgres.md

@@ -0,0 +1,24 @@
+# Importing an existing Postgres database from another installation (optional)
+
+Run this if you'd like to import your database from a previous installation of Matrix Synapse.
+(don't forget to import your `media_store` files as well - see [the restoring media store guide](restoring-media-store.md)).
+
+
+## Prerequisites
+
+For this to work, **the database name in Postgres must match** what this playbook uses.
+This playbook uses a Postgres database name of `homeserver` by default (controlled by the `matrix_postgres_db_name` variable).
+If your database name differs, be sure to change `matrix_postgres_db_name` to your desired name and to re-run the playbook before proceeding.
+
+The playbook supports importing Postgres dump files in **text** (e.g. `pg_dump > dump.sql`) or **gzipped** formats (e.g. `pg_dump | gzip -c > dump.sql.gz`).
+
+Before doing the actual import, **you need to upload your Postgres dump file to the server**.
+
+
+## Importing
+
+To import, run this command (make sure to replace `<server-path-to-postgres-dump.sql>` with a file path on your server):
+
+	ansible-playbook -i inventory/hosts setup.yml --extra-vars='server_path_postgres_dump=<server-path-to-postgres-dump.sql>' --tags=import-postgres
+
+**Note**: `<server-path-to-postgres-dump.sql>` must be a file path to a Postgres dump file on the server (not on your local machine!).

docs/installing.md

@@ -19,6 +19,8 @@ After installing, but before starting the services, you may want to do additiona
 
 - [Importing an existing SQLite database (from another installation)](importing-sqlite.md) (optional)
 
+- [Importing an existing Postgres database (from another installation)](importing-postgres.md) (optional)
+
 - [Restoring `media_store` data files from an existing installation](restoring-media-store.md) (optional)