At Wed, 2 Mar 2016 17:57:27 -0600, Jim Nasby <> wrote 
in <>
> On 3/2/16 5:41 PM, Tom Lane wrote:
> > Jim Nasby <> writes:
> >> On 3/2/16 4:21 PM, Peter Geoghegan wrote:
> >>> I think you should commit this. The chances of anyone other than you
> >>> and Masahiko recalling that you developed this tool in 3 years is
> >>> essentially nil. I think that the cost of committing a developer-level
> >>> debugging tool like this is very low. Modules like pg_freespacemap
> >>> currently already have no chance of being of use to ordinary users.
> >>> All you need to do is restrict the functions to throw an error when
> >>> called by non-superusers, out of caution.
> >>>
> >>> It's a problem that modules like pg_stat_statements and
> >>> pg_freespacemap are currently lumped together in the documentation,
> >>> but we all know that.
> >
> >> +1.
> >
> > Would it make any sense to stick it under src/test/modules/ instead of
> > contrib/ ?  That would help make it clear that it's a debugging tool
> > and not something we expect end users to use.
> I haven't looked at it in detail; is there something inherently
> dangerous about it?

I don't see any danger but the interface doesn't seem to fit use
by DBAs.

> When I'm forced to wear a DBA hat, I'd really love to be able to find
> out what VM status for a large table is. If it's in contrib they'll
> know the tool is there; if it's under src then there's about 0 chance
> of that. I'd think SU-only and any appropriate warnings would be
> enough heads-up for DBAs to be careful with it.

It looks to expose nothing about table contents. At lesast
anybody who can see the name of a table are safely allowable to
use this on it.

A possible usage (for me) of this would be directly couting
(un)vacuumed or (un)freezed pages in a relation. It would be
convenient that the 'freezed' and 'vacuumed' bits are in separate
integers. It would be usable even stats values for these bits are
shown in statistics views.


Kyotaro Horiguchi
NTT Open Source Software Center

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