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From: Robert Haas on 23 Jul 2010 15:00
On Fri, Jul 23, 2010 at 2:13 PM, Marko Tiikkaja
<marko.tiikkaja(a)cs.helsinki.fi> wrote:
> On 7/23/2010 8:52 PM, David Fetter wrote:
>>
>> On Thu, Jul 22, 2010 at 08:43:35PM +0300, Marko Tiikkaja wrote:
>>>
>>> Did I misunderstand the code? �And if I didn't, why do we do this
>>> differently?
>>
>> You mentioned in IRC that this was in aid of getting wCTEs going. �How
>> are these things connected?
>
> Currently, I'm trying to make wCTEs behave a bit like RULEs do. �But if
> every rewrite product takes a new snapshot, wCTEs will behave very
> unpredictably.
>
> But because EXPLAIN ANALYZE does *not* take a new snapshot for every rewrite
> product, I'm starting to think that maybe this isn't the behaviour we wanted
> to begin with?

Where should I be looking in the code for this?

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From: "Kevin Grittner" on 23 Jul 2010 18:45
Marko Tiikkaja <marko.tiikkaja(a)cs.helsinki.fi> wrote:

> I'm not sure what you mean by this; UPDATE and DELETE can take a
> look at the new tuple but that's completely separate from the
> snapshot.

Never mind -- I remembered that those could operate against tuples
not in the original snapshot, but forgot that they did it without
generating an actual fresh snapshot.

-Kevin

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From: Robert Haas on 23 Jul 2010 15:30
On Fri, Jul 23, 2010 at 3:19 PM, Marko Tiikkaja
<marko.tiikkaja(a)cs.helsinki.fi> wrote:
> This may be a bit hard to follow, but essentially what happens is that in
> EXPLAIN ANALYZE, the INSERT in the rule does not see the changes made by T2
> to baz while in the regular execution scenario it does.

Well that's gotta be a bug, but in what I'm not sure.

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From: Marko Tiikkaja on 23 Jul 2010 18:42
On 7/24/10 1:20 AM +0300, Alvaro Herrera wrote:
> It seems like it's EXPLAIN ANALYZE that needs fixing.

Yeah, looks like it. I see SQL functions also take a new snapshot for
every query.


Regards,
Marko Tiikkaja

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From: Robert Haas on 23 Jul 2010 18:43
On Fri, Jul 23, 2010 at 6:20 PM, Alvaro Herrera
<alvherre(a)commandprompt.com> wrote:
> Excerpts from Marko Tiikkaja's message of vie jul 23 17:44:21 -0400 2010:
>> On 7/24/10 12:37 AM +0300, Alvaro Herrera wrote:
>> > Excerpts from Marko Tiikkaja's message of vie jul 23 14:13:18 -0400 2010:
>
>> > I don't think it's fair game to change the behavior of multiple-output
>> > rules at this point. �However, I also think that it's unwise to base
>> > wCTEs on the behavior of rules -- rules are widely considered broken and
>> > unusable for nontrivial cases.
>>
>> I don't want to change the behaviour either, but we have two different
>> behaviours right now. �We need to change at least the other.
>
> It seems like it's EXPLAIN ANALYZE that needs fixing.

I would suggest that if we're going to change this, we back-patch it
to 9.0 before beta4.

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