Re: UPDATE of partition key

On Fri, May 12, 2017 at 3:07 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> I agree with you that it might not be straightforward to make it work,
> but now that earliest it can go is v11, do we want to try doing
> something other than just documenting it. What I could read from this
> e-mail thread is that you are intending towards just documenting it
> for the first cut of this feature. However, both Greg and Simon are of
> opinion that we should do something about this and even patch Author
> (Amit Khandekar) has shown some inclination to do something about this
> point (return error to the user in some way), so I think we can't
> ignore this point.
>
> I think now that we have some more time, it is better to try something
> based on a couple of ideas floating in this thread to address this
> point and see if we can come up with something doable without a big
> architecture change.
>
> What is your take on this point now?

I still don't think it's worth spending a bit on this, especially not
with WARM probably gobbling up multiple bits. Reclaiming the bits
seems like a good idea, but spending one on this still seems to me
like it's probably not the best use of our increasingly-limited supply
of infomask bits. Now, Simon and Greg may still feel otherwise, of
course.

I could get behind providing an option to turn this behavior on and
off at the level of the partitioned table. That would use a reloption
rather than an infomask bit, so no scarce resource is being consumed.
I suspect that most people don't update the partition keys at all (so
they don't care either way) and the ones who do are probably either
depending on EPQ (in which case they most likely want to just disallow
all UPDATE-row-movement) or not (in which case they again don't care).
If I understand correctly, the only people who will benefit from
consuming an infomask bit are the people who update their partition
keys AND depend on EPQ BUT only for non-key updates AND need the
system to make sure that they don't accidentally rely on it for the
case of an EPQ update. That seems (to me, anyway) like it's got to be
a really small percentage of actual users, but I just work here.

--
Robert Haas
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