Sample databases?

I am doing some testing and development on Postgres.

Is there, by chance, a good source of data which can be used as a test
database? I have been using a music database, but it is proprietary, and
makes me uncomfortable to post public tests.

What do you guys use?

Perhaps we can create a substantial test database? (Millions of records,
many tables, and a number of relations.) So when we see a problem, we
can all see it right away. I like "real world" data, because it is often
more organic than randomized test data, and brings out more issues. Take
index selection during a select, for instance.

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