Re: Tuples inserted and deleted by the same transaction

On Tue, Sep 13, 2022 at 11:04 AM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
>
> On Tue, 2022-09-13 at 11:47 +0300, Nikita Malakhov wrote:
> > On Tue, Sep 13, 2022 at 11:06 AM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
> > > Shouldn't such tuples be considered dead right away, even if the inserting
> > > transaction is still active?  That would allow cleaning them up even before
> > > the transaction is done.
> > >
> > > There is this code in HeapTupleSatisfiesVacuumHorizon:
> > >
> > >         else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
> > >         {
> > >             [...]
> > >             /* inserted and then deleted by same xact */
> > >             if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetUpdateXid(tuple)))
> > >                 return HEAPTUPLE_DELETE_IN_PROGRESS;
> > >
> > > Why HEAPTUPLE_DELETE_IN_PROGRESS and not HEAPTUPLE_DEAD?
> >
> > Please correct me if I'm wrong, despite tuples being inserted and deleted by the same
> > transaction - they are visible inside the transaction and usable by it, so considering them
> > dead and cleaning up during execution is a bad idea until the transaction is ended.
>
> But once they are deleted or updated, even the transaction that created them cannot
> see them any more, right?

Forgive me if this is not related but if there is a savepoint between
the insertion and deletion, wouldn't it be possible for the
transaction to recover the deleted tuples?

Best regards
Pantelis Theodosiou