Re: Allow ERROR from heap_prepare_freeze_tuple to be downgraded to WARNING

On 2020-Jul-20, Dilip Kumar wrote:

> On Fri, Jul 17, 2020 at 4:16 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:

> > So if the vacuum_tolerate_damage is set then in
> > all the cases in heap_prepare_freeze_tuple where the corrupted xid is
> > detected, it will emit a warning and return that nothing is changed in
> > the tuple and the 'tuple_totally_frozen' will also be set to false.
> > Since we are returning false the caller will not try to freeze such
> > tuple and the tuple_totally_frozen is also set to false so that the
> > page will not be marked to all frozen even if all other tuples in the
> > page are frozen.

> Robert has mentioned at [1] that we probably should refuse to update
> 'relfrozenxid/relminmxid' when we encounter such tuple and emit
> WARNING instead of an error.

Isn't this already happening per your description above?

> I think we shall do that in some cases
> but IMHO it's not a very good idea in all the cases. Basically, if
> the xmin precedes the relfrozenxid then probably we should allow to
> update the relfrozenxid whereas if the xmin precedes cutoff xid and
> still uncommitted then probably we might stop relfrozenxid from being
> updated so that we can stop CLOG from getting truncated.

I'm not sure I understand 100% what you're talking about here (the first
half seems dangerous unless you misspoke), but in any case it seems a
pointless optimization. I mean, if the heap is corrupted, you can hope
to complete the vacuum (which will hopefully return which *other* tuples
are similarly corrupt) but trying to advance relfrozenxid is a lost
cause.

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Álvaro Herrera https://www.2ndQuadrant.com/
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