1 files changed, 83 insertions, 14 deletions
diff --git a/docs/postgres.md b/docs/postgres.md
index 29cf762858..70fe29cdcc 100644
--- a/docs/postgres.md
+++ b/docs/postgres.md
@@ -27,17 +27,21 @@ connect to a postgres database.
 
 ## Set up database
 
-Assuming your PostgreSQL database user is called `postgres`, create a
-user `synapse_user` with:
+Assuming your PostgreSQL database user is called `postgres`, first authenticate as the database user with:
 
     su - postgres
+    # Or, if your system uses sudo to get administrative rights
+    sudo -u postgres bash
+
+Then, create a user ``synapse_user`` with:
+
     createuser --pwprompt synapse_user
 
 Before you can authenticate with the `synapse_user`, you must create a
 database that it can access. To create a database, first connect to the
 database with your database user:
 
-    su - postgres
+    su - postgres # Or: sudo -u postgres bash
     psql
 
 and then run:
@@ -57,7 +61,50 @@ Note that the PostgreSQL database *must* have the correct encoding set
 
 You may need to enable password authentication so `synapse_user` can
 connect to the database. See
-<https://www.postgresql.org/docs/11/auth-pg-hba-conf.html>.
+<https://www.postgresql.org/docs/current/auth-pg-hba-conf.html>.
+
+If you get an error along the lines of `FATAL:  Ident authentication failed for
+user "synapse_user"`, you may need to use an authentication method other than
+`ident`:
+
+* If the `synapse_user` user has a password, add the password to the `database:`
+  section of `homeserver.yaml`. Then add the following to `pg_hba.conf`:
+
+  ```
+  host    synapse     synapse_user    ::1/128     md5  # or `scram-sha-256` instead of `md5` if you use that
+  ```
+
+* If the `synapse_user` user does not have a password, then a password doesn't
+  have to be added to `homeserver.yaml`. But the following does need to be added
+  to `pg_hba.conf`:
+
+  ```
+  host    synapse     synapse_user    ::1/128     trust
+  ```
+
+Note that line order matters in `pg_hba.conf`, so make sure that if you do add a
+new line, it is inserted before:
+
+```
+host    all         all             ::1/128     ident
+```
+
+### Fixing incorrect `COLLATE` or `CTYPE`
+
+Synapse will refuse to set up a new database if it has the wrong values of
+`COLLATE` and `CTYPE` set, and will log warnings on existing databases. Using
+different locales can cause issues if the locale library is updated from
+underneath the database, or if a different version of the locale is used on any
+replicas.
+
+The safest way to fix the issue is to take a dump and recreate the database with
+the correct `COLLATE` and `CTYPE` parameters (as shown above). It is also possible to change the
+parameters on a live database and run a `REINDEX` on the entire database,
+however extreme care must be taken to avoid database corruption.
+
+Note that the above may fail with an error about duplicate rows if corruption
+has already occurred, and such duplicate rows will need to be manually removed.
+
 
 ## Tuning Postgres
 
@@ -83,19 +130,41 @@ of free memory the database host has available.
 When you are ready to start using PostgreSQL, edit the `database`
 section in your config file to match the following lines:
 
-    database:
-        name: psycopg2
-        args:
-            user: <user>
-            password: <pass>
-            database: <db>
-            host: <host>
-            cp_min: 5
-            cp_max: 10
+```yaml
+database:
+  name: psycopg2
+  args:
+    user: <user>
+    password: <pass>
+    database: <db>
+    host: <host>
+    cp_min: 5
+    cp_max: 10
+```
 
 All key, values in `args` are passed to the `psycopg2.connect(..)`
 function, except keys beginning with `cp_`, which are consumed by the
-twisted adbapi connection pool.
+twisted adbapi connection pool. See the [libpq
+documentation](https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-PARAMKEYWORDS)
+for a list of options which can be passed.
+
+You should consider tuning the `args.keepalives_*` options if there is any danger of
+the connection between your homeserver and database dropping, otherwise Synapse
+may block for an extended period while it waits for a response from the
+database server. Example values might be:
+
+```yaml
+# seconds of inactivity after which TCP should send a keepalive message to the server
+keepalives_idle: 10
+
+# the number of seconds after which a TCP keepalive message that is not
+# acknowledged by the server should be retransmitted
+keepalives_interval: 10
+
+# the number of TCP keepalives that can be lost before the client's connection
+# to the server is considered dead
+keepalives_count: 3
+```
 
 ## Porting from SQLite