Re: Toast issues with OldestXmin going backwards

On Fri, Apr 27, 2018 at 11:35 AM, Andrew Gierth
<andrew(at)tao11(dot)riddles(dot)org(dot)uk> wrote:
>>>>>> "Robert" == Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Robert> One idea that occurred to me is to somehow record -- I guess in
> Robert> pg_class using non-transactional updates -- the last cutoff XID
> Robert> used to vacuum any given table. Then we could just make a rule
> Robert> that you can't vacuum the TOAST table with an XID that's newer
> Robert> than the last one used for the main table. That would preserve
> Robert> the property that you can vacuum the tables separately while
> Robert> avoiding dangling pointers. But that's obviously not
> Robert> back-patchable,
>
> The suggestion made previously (in a historical thread) was to use an
> entry in the reloptions field for this, at least in back branches. It
> would be necessary for vacuum to add the entry initially in a normal
> transactional update, after which it could be updated inplace.

Yeah, I suppose. Sounds pretty rickety to me, though. Maybe I'm just
a pessimist.

--
Robert Haas
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