Re: Inline Extension

On Mon, Jan 23, 2012 at 7:59 PM, Daniel Farina <daniel(at)heroku(dot)com> wrote:
> Things are still a bit ugly in the more complex cases: consider
> PostGIS's linkage against libproj and other libraries.  In order to
> cover all cases, I feel that what I need is an optional hook (for the
> same of argument, let's say it's another "command" type hook, e.g.
> "archive_command") to be executed when extension (un)installation is
> occurs on a primary or is replayed on a standby whereby I can acquire
> the necessary dependencies for an extension or signal some kind of
> error (as to exactly how that interfaces with the server is delicate,
> should one want to supply good error messages to the user).

There aren't a whole lot of good options for handling errors on the
standby, in general. If the operation has already occurred on the
master, it's too late to decide that we're not going to have it happen
on the standby as well.

Of course, if we confine ourselves to control and SQL files, then it
doesn't really matter: the catalog entries from the master will make
it to the standby regardless of the absence of the SQL and control
files, and maybe we could simply decide that the operations which
write in pg_extension aren't WAL-logged and can be separately
performed on the standby if you want them there as well.

But, that's a bit unlike how we normally do things. And if we're
going to WAL-log the writing of the extension files, then I start to
feel like we should go back to putting the data in a system catalog
rather than the filesystem, because inventing a new WAL record type
for this seems like it will make things quite a bit more complicated
for no particular benefit.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company