A few years back I had some experience using this tool to migrate a MySQL database to a PostgreSQL. As far as I remember it was quite pleasant.
I had the some trouble with MySQL accepting invalid dates (like 0000-00-00) while Postgres rejects such dates. However, there was an option to convert such dates to NULL which saved the day.
Also you have to manually rewrite your views. Since we had a lot and also very complicated views I ended up materializing each MySQL view, manually porting it to Postgres and then comparing the result. That worked quite well.
In 2013 I was migrating a mysql database to postgres, for a tech demo as I'm a bit of a fan of postgres.
What followed was pgloader spitting out millions of errors, I assumed I had used the tool wrong or it was broken; but the more I looked at it the more I realised that we'd been suffering silent data corruption for years- and postgresql wouldn't validate the invalid data.
Oh, and the datetime thing, that was annoying. Fun things used to happen with mysql when you had a NOT NULL constraint but didn't specify a default.
I had the some trouble with MySQL accepting invalid dates (like 0000-00-00) while Postgres rejects such dates. However, there was an option to convert such dates to NULL which saved the day.
Also you have to manually rewrite your views. Since we had a lot and also very complicated views I ended up materializing each MySQL view, manually porting it to Postgres and then comparing the result. That worked quite well.