First bit of documentation for PostgreSQL added.

postgresql/README.md

@@ -3,8 +3,74 @@ gitea: none
 include_toc: true
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-# PostgreSQL database
+# Installing PostgreSQL and creating database and user
+
+Installing [PostgreSQL](https://www.postgresql.org/) on Debian is very easy:
+
+```
+apt install postgresql python3-psycopg
+
+sudo -u postgres bash
+
+createuser --pwprompt synapse
+createdb --encoding=UTF8 --locale=C --template=template0 --owner=synapse synapse
+
+```
+
+After this, PostgreSQL is installed, the database `synapse` exists and so does
+the database user `synapse`. Make sure you choose a strong password.
 
 
+# Configuring access
+
+After a clean installation, PostgreSQL will listen on localhost, both IPv4 and
+IPv6 (if available). In many cases, this is exactly what you want.
+
+## Network
+
+PostgreSQL will listen on localhost, this is configured in
+`/etc/postgresql/<version>/main/postgresql.conf`:
+
+```
+listen_addresses = 'localhost'
+```
+
+This line is usually commented out, but as it is the default, it's really
+there.
 
 
+## UNIX socket
+
+If you want PostgreSQL to listen only to a local UNIX socket (more efficient
+than network and -depending on the configuration of the rest of you system-
+easier to protect), make the aforementioned option explicitly empty and
+uncomment it:
+
+```
+listen_addresses =
+```
+
+Check these options to make sure the socket is placed in the right spot and
+given the correct permissions:
+
+```
+unix_socket_directories = '/var/run/postgresql'
+#unix_socket_group = ''
+#unix_socket_permissions = 0777
+```
+
+
+## Permissions
+
+Add permission for the user to connect to the database from localhost (if
+PostgreSQL listens on localhost), or the socket (if you use that). This is
+configured in `/etc/postgresql/<version>/main/pg_hba.conf`:
+
+```
+local    synapse     synapse     password                     # for use with UNIX sockets
+host     synapse     synapse     localhost       md5          # for use with localhost network
+```
+
+Make sure you add these lines under the one that gives access to the postgres
+superuser, the first line.
+