Tom Lane schrieb am 06.02.2021 um 18:09:
>> I have noticed that when I look at pg_available_extensions many
>> extensions are listed with multiple versions even though only the
>> latest one is actually used.
>
> Yes, that view is supposed to list the versions that are available
> to be installed. Typically, installation scripts for several back
> versions exist on disk. This is an artifact of the way that we
> approach providing extension upgrade capability, but it can be handy
> if you want to test SQL code against back versions.
>
> As an example, contrib/adminpack installs
>
> adminpack--1.0.sql
> adminpack--1.0--1.1.sql
> adminpack--1.1--2.0.sql
> adminpack--2.0--2.1.sql
>
> Ordinarily, when you "create extension adminpack", it runs all four
> of those scripts in sequence and you end up with the 2.1 SQL objects.
> But if you ask to install some earlier version, it just stops after
> the appropriate script. So pg_available_extensions shows 1.0, 1.1,
> 2.0, and 2.1 as available versions. (Of course, the main reason
> for having the delta scripts is to support "alter extension upgrade".)
So if it is expected to see multiple versions through that view,
then why do the multiple versions go away when I dump & reload
the database?