Re: allow_system_table_mods stuff

Hi,

On 2019-06-21 16:37:16 -0400, Tom Lane wrote:
> We do have to get past the compatibility issue though. My thought was
> that for a period of N years we could force allow_system_table_dml = on
> while running extension scripts, and then cease doing so. This would
> give extension authors a reasonable window in which their scripts would
> work in either old or new backends. At some point in that time they'd
> probably have occasion to make other changes that render their scripts
> not backwards compatible, at which point they can insert "SET
> allow_system_table_dml = on" so that the script keeps working when we
> remove the compatibility hack.

I'd modify this approach by having a allow_system_table_dml level that
warns when DDL to system tables is performed, and then set
allow_system_table_dml to that when processing extension scripts (and
perhaps modify the warning message when creating_extension ==
true). That way it'd be easier to spot such extension scripts.

And I'd personally probably just set allow_system_table_dml to warn when
working interactively, just to improve logging etc.

> This line of thought leads to the conclusion that we do want
> separate "allow_system_table_dml" and "allow_system_table_ddl"
> bools. Otherwise, the backwards-compatibility hack would need
> to turn on a level of unsafety that extension scripts have *not*
> had before and surely shouldn't have by default.

+1

Greetings,

Andres Freund