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?
