> + If the old cluster used extensions, whether from > + <filename>contrib</filename> or some other source, it used > + shared object files (or DLLs) to implement these extensions, e.g., > + <filename>pgcrypto.so</filename>. Now, shared object files matching > + the new server binary must be installed in the new cluster, usually > + via operating system commands. Do not load the schema definitions, > + e.g., <command>CREATE EXTENSION pgcrypto</command>, because these > + will be copied from the old cluster. (Extensions should be upgraded > + later using <literal>ALTER EXTENSION ... UPGRADE</literal>.)
I propose this:
<para> If the old cluster used shared-object files (or DLLs) for extensions or other loadable modules, install recompiled versions of those files onto the new cluster. Do not install the extension themselves (i.e., do not run <command>CREATE EXTENSION</command>), because extension definitions will be carried forward from the old cluster. </para>
<para> Extensions can be upgraded after pg_upgrade completes using <command>ALTER EXTENSION ... UPGRADE</command>, on a per-database basis. </para>
I suggest " ... for extensions or other loadable modules" because loadable modules aren't necessarily for extensions. Also, it's perfectly possible to have extension that don't have a loadable module.
I suggest "extension definitions ... carried forward" instead of "extensions ... copied" (your proposed text) to avoid the idea that files are copied; use it instead of "schema definitions ... upgraded" (the current docs) to avoid the idea that they are actually upgraded; also, "schema definition" seems a misleading term to use here.
I like "carried forward", however it presumes quite a bit of knowledge of what is going on inside pg_upgrade.
That said I don't have a better option short of explaining the whole thing which is clearly out of scope.
I suggest "can be upgraded" rather than "should be upgraded" because we're not making a recommendation, merely stating the fact that it is possible to do so.
Why not recommend it? I was going to suggest that we actually run alter extension upgrade ... on all of them as a solution.
What are the downsides to upgrading them all by default ? AFAIK if they need upgrading this should run all of the SQL scripts, if they don't then this should be a NO-OP.
