Re: Reviewing freeze map code

On Mon, Jun 6, 2016 at 11:44 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> In terms of diagnostic tools, you can get the VM bits and
>> page-level bits using the pg_visibility extension; I wrote it
>> precisely because of concerns like the ones you raise here. If you
>> want to cross-check the page-level bits against the tuple-level bits,
>> you can do that with the pageinspect extension. And if you do those
>> things, you can actually find out whether stuff is broken.
>
> That's WAY out ouf reach of any "normal users". Adding a vacuum option
> is doable, writing complex queries is not.

Why would they have to write the complex query? Wouldn't they just
need to run that we wrote for them?

I mean, I'm not 100% dead set against this option you want, but in all
honestly, I would never, ever tell anyone to use it. Unleashing
VACUUM on possibly-damaged data is just asking it to decide to prune
away tuples you don't want gone. I would try very hard to come up
with something to give that user that was only going to *read* the
possibly-damaged data with as little chance of modifying or erasing it
as possible.

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