Re: Do we need to handle orphaned prepared transactions in the server?

On Thu, Apr 16, 2020 at 03:11:51PM -0400, Tom Lane wrote:
> Even if I liked the core idea, loading the functionality onto VACUUM seems
> like a fairly horrid design choice.  It's quite unrelated to what that
> command does.  In the autovac code path, it's going to lead to multiple
> autovac workers all complaining simultaneously about the same problem.
> But having manual vacuums complain about issues unrelated to the task at
> hand is also a seriously poor bit of UX design.  Moreover, that won't do
> all that much to surface problems, since most(?) installations never run
> manual vacuums; or if they do, the "manual" runs are really done by a cron
> job or the like, which is not going to notice the warnings.  So you still
> need a log-scraping tool.

+1.

> If we were going to go down the path of periodically logging warnings
> about old prepared transactions, some single-instance background task
> like the checkpointer would be a better place to do the work in.  But
> I'm not really recommending that, because I agree with Robert that
> we just plain don't want this functionality.

I am not sure that the checkpointer is a good place to do that either,
joining back with your argument in the first paragraph of this email
related to vacuum.  One potential approach would be a contrib module
that works as a background worker?  However, I would think that
finding a minimum set of requirements that we think are generic enough
for most users would be something hard to draft a list of.  If we had
a small, minimal contrib/ module in core that people could easily
extend for their own needs and that we would intentionally keep as
minimal, in the same spirit as say passwordcheck, perhaps..
--
Michael