Re: Reviewing freeze map code

On Tue, May 10, 2016 at 11:30 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Mon, May 9, 2016 at 7:40 PM, Ants Aasma <ants.aasma@eesti.ee> wrote:
>> On Mon, May 9, 2016 at 10:53 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>>> On Sun, May 8, 2016 at 10:42 PM, Masahiko Sawada <sawada.mshk@gmail.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

Or second way I came up with is having tool to remove particular _vm
file safely, which is executed via SQL or client tool like
pg_resetxlog.

Attached updated VACUUM SCAN_ALL patch.
Please find it.

Regards,

--
Masahiko Sawada