Matthew Pounsett <matt@conundrum.com> writes:
> [...] Is there any rule of thumb for making sure one has enough space
> available for the upgrade?
No, because it depends greatly on which version you are upgrading from
and which version you are upgrading to etc.
Perhaps you could carve out a slice of data, e.g. 1 GB and load it into
a test database and try to upgrade that. That would probably give you an
idea.
Also, you mentioned that your database contains historical test data¹,
then I would guess that one of the indexes is related to timestamps? But
maybe you could live with a smaller BRIN index for the timestamps:
https://www.postgresql.org/docs/11/brin-intro.html - that could
potentially save some space, and may not have been something on the
radar when the database was first developed.
Best regards,
Jacob
¹) I think I know which kind of data based on your progress reports on
a DNS related list I'm subscribed to.