Re: Allow ERROR from heap_prepare_freeze_tuple to be downgraded to WARNING

On Tue, Sep 15, 2020 at 11:14 AM Andres Freund <andres@anarazel.de> wrote:
>
> On 2020-09-15 10:54:29 +0530, Dilip Kumar wrote:
> > What problem do you see if we set xmax to the InvalidTransactionId and
> > HEAP_XMAX_INVALID flag in the infomask ?
>
> 1) It'll make a dead tuple appear live. You cannot do this for tuples
>    with an xid below the horizon.

How is it possible?  Because tuple which has a committed xmax and the
xmax is older than the oldestXmin, should not come for freezing unless
it is lock_only xid (because those tuples are already gone).  So if
the xmax is smaller than the cutoff xid than either it is lock_only or
it is aborted.  If the XMAX is lock only then I don't see any issue
OTOH if it is aborted xid and if it is already smaller than the
cut-off xid then it is anyway live tuple.

>2) it'll break HOT chain following / indexes.

If my above theory in point 1 is correct then I don't see this issue as well.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com