Re: nested xacts and phantom Xids

Added to TODO, just so we don't forget later:

    * Use a phantom command counter for nested subtransactions to reduce
          tuple overhead


---------------------------------------------------------------------------

Tom Lane wrote:
> Alvaro Herrera <alvherre@dcc.uchile.cl> writes:
> > Hmm ... yes, this could be very ugly indeed, but I haven't even looked
> > at the executor code so I can't comment.  Are executor nodes copyable?
>
> Nope, and even if we had support for that the executor tree per se
> is just the tip of the iceberg.  There's also indexscan status, SRF
> function internal state, yadda yadda.  I think the odds of doing
> something with all that stuff for 7.5 are exactly zero ... we'd better
> define a stopgap behavior.
>
> > Oh, and I've been playing with large objects and I've encountered bugs
> > elsewhere.  I'll look at it with the new patch you just posted.
>
> Wouldn't surprise me, we've not looked at that yet either.
>
> I do feel that we have enough things working that we should commit to
> nested transactions for 7.5.  There will be some things that we have to
> restrict, such as cursors and perhaps large objects.  But it's surely
> better than no subtransactions at all.
>
>             regards, tom lane
>
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