Re: RFC: Logging plan of the running query

On Fri, Feb 16, 2024 at 12:29 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> If we went with something like tht approach, I think we'd have to do something
> like redirecting node->ExecProcNode to a wrapper, presumably from within a
> CFI. That wrapper could then implement the explain support, without slowing
> down the normal execution path.

That's an annoying complication; maybe there's some better way to
handle this. But I think we need to do something different than what
the patch does currently because...

> > It's really hard for me to accept that the heavyweight lock problem
> > for which the patch contains a workaround is the only one that exists.
> > I can't see any reason why that should be true.
>
> I suspect you're right.

...I think the current approach is just plain dead, because of this
issue. We can't take an approach that creates an unbounded number of
unclear reentrancy issues and then insert hacks one by one to cure
them (or hack around them, more to the point) as they're discovered.

The premise has to be that we only allow logging the query plan at
points where we know it's safe, rather than, as at present, allowing
it in places that are unsafe and then trying to compensate with code
elsewhere. That's not likely to ever be as stable as we want
PostgreSQL to be.

--
Robert Haas
EDB: http://www.enterprisedb.com