MariaDB Exporter 0.21.0-2

mysqld_exporter gives Prometheus the NAS's MariaDB (WD's own, or the MariaDB app's) metrics - queries, connections, InnoDB's buffer pool, locks and table caches - with a Grafana dashboard. It's for the Prometheus and Grafana apps: once they're installed (in any order), Prometheus collects its metrics every 30 seconds, and its dashboard (MariaDB / MySQL) is in Grafana's NAS folder. It runs natively on the NAS (no Docker).

• For the NAS's MariaDB: WD's own, or the MariaDB app's (the same socket, /var/lib/mysql/mysql.sock). It logs in as mysqld_exporter@localhost, a login the app creates (as root, over the socket) with a password only it keeps, which can read MariaDB's status (PROCESS, REPLICATION CLIENT and performance_schema), not your data. If MariaDB isn't running when it starts, the login is set up as soon as it answers.
• It listens on the NAS itself only (127.0.0.1:9104) and runs as its own user (mysqld_exporter, ID 90). Its files are kept in Nas_Prog/_mysqld_exporter, across reinstalls and removal.
• Its page shows whether it reaches MariaDB, whether Prometheus collects its metrics, and links to its dashboard. Set up its login again makes a new password (e.g. after switching between WD's MariaDB and the MariaDB app's).
• Its scrape job is prometheus/mysql.yml and its dashboard dashboards/mariadb.json: the Prometheus and Grafana apps pick up every app's (see their READMEs), and drop them when the app is removed.
• The dashboard is mysqld_exporter's own dashboard (mysqld-mixin/dashboards/mysql-overview.json, Apache-2.0), unchanged apart from its title, a nas tag, and two settings MariaDB no longer has taken out of its memory panel (InnoDB's additional memory pool, TokuDB's cache). Its process states panels use the process list collector, which the app turns on.
• It's the official static program, checked against the SHA256 its release publishes (pinned in static/mysqld_exporter/build.sh). For the Intel and ARM models (the ARM ones' packages are checked under emulation when they're built, but haven't yet been tried on an ARM NAS) - on an ARM NAS it watches WD's own MariaDB, if it has one (the MariaDB app is for the Intel models only).