How to find what is using my database disc space? DB using 4xtimes the space it should

Questions & Answers
#1

Received a warning that my database is running out of disc space (even so it should not).

Warning, XXX has less than 20% disk space available

Warning:less than 197.95 MB available disk space Disk
Source:Master (master) / db

The import file used to fill the database is about 90MB in size.
And that seems to inflate in the database to around 210MB

MariaDB [main]> SELECT table_schema AS "Database", 
    -> ROUND(SUM(data_length + index_length) / 1024 / 1024, 2) AS "Size (MB)" 
    -> FROM information_schema.TABLES 
    -> GROUP BY table_schema;
+--------------------+-----------+
| Database           | Size (MB) |
+--------------------+-----------+
| information_schema |      0.19 |
| main               |    210.14 |
+--------------------+-----------+
2 rows in set (0.04 sec)

The platform tool says it is 619MiB (<= why? who is using the extra 400 MiB?)

Checking database service db...

+----------------+-----------------+--------+
| Allocated disk | Estimated usage | % used |
+----------------+-----------------+--------+
| 1.0 GiB        | 619.4 MiB       | ~ 60%  |
+----------------+-----------------+--------+

And why does the tool say around 60% are used but the warning says over 80% are used.

How do I find out who is using the extra 600MB of database space and how do I stop that from happening?

Just in case it is of relevance. This is my database setting:
db:
type: mariadb:10.4
disk: 1024