RFC: Drop support for very old versions of PostgreSQL

[RealOrangeOne]

Currently, pgautoupgrade has support for upgrading versions as far back as 9.6. PostgreSQL 9.6 hasn't had a release since late 2021, when it lost active support.

Dropping support for very old versions keeps the images smaller (currently compressed images are ~1.6x than standard postgres builds), and likely improves build time and maintenance. Therefore, I'd suggest dropping support for versions older than 12.

Keeping EoL versions likely makes sense, but perhaps only the oldest version? If users need to upgrade their 9.6 DB, it's not unreasonable for them to have to do it in 2 jumps rather than 1.

[andyundso]

maintenance for these old versions is actually not a big deal. compared to what you would expect, all of these old versions build perfectly without any code changes on recent Alpine and Debian versions. Although this could change at some point.

but otherwise I think your suggestion is reasonable. Likely the image will still have ~1.4x the size of the main Postgres image, since newer versions of Postgres tend to be larger in size.

[justinclift]

Personally, I'd probably keep the old versions around for a few more years. 😄