Re: pg_upgrade does not upgrade pg_stat_statements properly

On 7/29/21 11:10 AM, Bruce Momjian wrote:
> On Thu, Jul 29, 2021 at 11:01:43AM -0400, Dave Cramer wrote:
>> Much better, however I'm unclear on whether CREATE EXTENSION is actually
>> executed on the upgraded server.
>>
>> From what I could gather it is not, otherwise the new function definitions
>> should have been in place.
>> I think what happens is that the function definitions are copied as part of the
>> schema and pg_extension is also copied.
>
> Yes, the _effect_ of CREATE EXTENSION in the old cluster is copied to
> the new cluster as object definitions. CREATE EXTENSION runs the SQL
> files associated with the extension.
>

This assumes that the scripts executed during CREATE EXTENSION have no
conditional code in them that depends on the server version. Running the
same SQL script on different server versions can have different effects.

I don't have a ready example of such an extension, but if we ever would
convert the backend parts of Slony into an extension, it would be one.

Regards, Jan

--
Jan Wieck