Use C collation for Postgres to appease Synapse

CHANGELOG.md

@@ -1,3 +1,20 @@
+# 2020-01-21
+
+## Postgres collation changes (action required!)
+
+By default, we've been using a UTF-8 collation for Postgres. This is known to cause Synapse some troubles (see the [relevant issue](https://github.com/matrix-org/synapse/issues/6722)) on systems that use [glibc](https://www.gnu.org/software/libc/). We run Postgres in an [Alpine Linux](https://alpinelinux.org/) container (which uses [musl](https://www.musl-libc.org/), and not glibc), so our users are likely not affected by the index corruption problem observed by others.
+
+Still, we might become affected in the future. In any case, it's imminent that Synapse will complain about databases which do not use a C collation.
+
+To avoid future problems, we recommend that you run the following command:
+
+```
+ansible-playbook -i inventory/hosts setup.yml --tags=upgrade-postgres --extra-vars='{"postgres_force_upgrade": true}'
+```
+
+It forces a [Postgres database upgrade](docs/maintenance-postgres.md#upgrading-postgresql), which would recreate your Postgres database using the proper (`C`) collation. If you are low on disk space, or run into trouble, refer to the Postgres database upgrade documentation page.
+
+
 # 2020-01-14
 
 ## Added support for Appservice Webhooks

roles/matrix-postgres/tasks/upgrade_postgres.yml

@@ -20,6 +20,11 @@
     postgres_start_wait_time: 15
   when: "postgres_start_wait_time|default('') == ''"
 
+- name: Set postgres_force_upgrade, if not provided
+  set_fact:
+    postgres_force_upgrade: false
+  when: "postgres_force_upgrade|default('') == ''"
+
 - name: Fail, if trying to upgrade external Postgres database
   fail:
     msg: "Your configuration indicates that you're not using Postgres from this role. There is nothing to upgrade."
@@ -45,7 +50,7 @@
 - name: Abort, if already at latest Postgres version
   fail:
     msg: "You are already running the latest Postgres version supported ({{ matrix_postgres_docker_image_latest }}). Nothing to do"
-  when: "matrix_postgres_detected_version_corresponding_docker_image == matrix_postgres_docker_image_latest"
+  when: "matrix_postgres_detected_version_corresponding_docker_image == matrix_postgres_docker_image_latest and not postgres_force_upgrade"
 
 - debug:
     msg: "Upgrading database from {{ matrix_postgres_detected_version_corresponding_docker_image }} to {{ matrix_postgres_docker_image_latest }}"

roles/matrix-postgres/templates/env-postgres-server.j2

@@ -1,4 +1,7 @@
 #jinja2: lstrip_blocks: "True"
 POSTGRES_USER={{ matrix_postgres_connection_username }}
 POSTGRES_PASSWORD={{ matrix_postgres_connection_password }}
-POSTGRES_DB={{ matrix_postgres_db_name }}
+POSTGRES_DB={{ matrix_postgres_db_name }}
+# Synapse refuses to run if collation is not C.
+# See https://github.com/matrix-org/synapse/issues/6722
+POSTGRES_INITDB_ARGS=--lc-collate C --lc-ctype C --encoding UTF8