Re: Reviewing freeze map code

On Mon, May 9, 2016 at 7:40 PM, Ants Aasma <ants(dot)aasma(at)eesti(dot)ee> wrote:
> On Mon, May 9, 2016 at 10:53 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Sun, May 8, 2016 at 10:42 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>>> Attached draft patch adds SCANALL option to VACUUM in order to scan
>>> all pages forcibly while ignoring visibility map information.
>>> The option name is SCANALL for now but we could change it after got consensus.
>>
>> If we're going to go that way, I'd say it should be scan_all rather
>> than scanall. Makes it clearer, at least IMHO.
>
> Just to add some diversity to opinions, maybe there should be a
> separate command for performing integrity checks. Currently the best
> ways to actually verify database correctness do so as a side effect.
> The question that I get pretty much every time after I explain why we
> have data checksums, is "how do I check that they are correct" and we
> don't have a nice answer for that now. We could also use some ways to
> sniff out corrupted rows that don't involve crashing the server in a
> loop. Vacuuming pages that supposedly don't need vacuuming just to
> verify integrity seems very much in the same vein.
>
> I know right now isn't exactly the best time to hastily slap on such a
> feature, but I just wanted the thought to be out there for
> consideration.

I think that it's quite reasonable to have ways of performing an
integrity check that are separate from VACUUM, but this is about
having a way to force VACUUM to scan all-frozen pages - and it's hard
to imagine that we want a different command name for that.

--
Robert Haas
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