Bug#839182: postgresql-9.4-postgis-2.2 and postgresql-9.4-postgis-2.1 cannot be installed simultaneously

[Greg Burek]

On Fri, 30 Sep 2016 08:00:52 +0200 Markus Wanner <markus at bluegap.ch> wrote:
> Control: tags -1 +confirmed
>
> Hello Greg,
>
> On 09/29/2016 11:59 PM, Greg Burek wrote:
> > Is each version of postgis-scripts incompatible with other versions of
> > postgis?
>
> Yes.
>
> Longer answer: the base issue here is that PostGIS is a single
> extension, so PostgreSQL wants exactly *one* file from a scripts package
> that defines what to do for `CREATE EXTENSION postgis`. These scripts
> packages all ship that one file, therefore they are not possible
> co-installable and must conflict.

Ah ok I understand now.

>
> > Is postgis-2.3-scripts not backwards compatible with postgis-2.2?
>
> If the extension is already created for a given database, PostgreSQL
> doesn't need the -scripts package(s) at all. You could (in theory)
> remove them.

This is great, as we frequently work with base backups that require older
postgis binaries, but want all new extensions to use the latest available
versions. Having the latest scripts package satisfy dependencies for all
previous versions gives us the ability to do this.

>
> In practice, we made the extension package depend on its exact -scripts
> counterpart, which makes the postgresql-X.Y-postgis-M.N packages
> non-co-installable as well. We need to fix that.

This sounds right.

Ideally, all postgis packages should require `postgis-scripts` dummy
package, which then depends on the latest available, in this case
`postgis-2.3-scripts`.

This would allow `postgis-2.1`, `postgis-2.2` and `postgis-2.3` to be
installed to work with older databases that require those specific versions
of postgis, while `postgis-2.3-scripts` is then available for new uses of
`CREATE EXTENSION` with `postgis-2.3`.

>
> Thanks for your report, I wasn't aware of this issue so far.
>
> Kind Regards
>
> Markus Wanner
>
>
>
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