Re: Two different methods of sneaking non-immutable data into an index

mmoncure(at)gmail(dot)com (Merlin Moncure) writes:
> On Thu, Aug 5, 2010 at 12:59 PM, Chris Browne <cbbrowne(at)acm(dot)org> wrote:
>> mmoncure(at)gmail(dot)com (Merlin Moncure) writes:
>>> On Wed, Aug 4, 2010 at 9:31 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>>>> On Wed, Aug 4, 2010 at 6:43 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
>>>>> *) also, isn't it possible to change text cast influencing GUCs 'n'
>>>>> times per statement considering any query can call a function and any
>>>>> function can say, change datestyle?  Shouldn't the related functions
>>>>> be marked 'volatile', not stable?
>>>>
>>>> This is just evil.  It seems to me that we might want to instead
>>>> prevent functions from changing things for their callers, or
>>>> postponing any such changes until the end of the statement, or, uh,
>>>> something.  We can't afford to put ourselves in a situation of having
>>>> to make everything volatile; at least, not if "performance" is
>>>> anywhere in our top 50 goals.
>>>
>>> yeah -- perhaps you shouldn't be allowed set things like datestyle in
>>> functions then.  I realize this is a corner (of the universe) case,
>>> but I can't recall any other case of volatility being relaxed on
>>> performance grounds... :-).  Maybe a documentation warning would
>>> suffice?
>>
>> That would cause grief for Slony-I, methinks, and probably other things
>> that behave somewhat similar.
>>
>> The "logtrigger()" function coerces datestyle to ISO, so that when dates
>> get stored, they are stored in a canonical form, irrespective of an
>> individual connection's decisions on datestyle, so we don't have to
>> include datestyle information as part of the replicated data.
>
> hm -- interesting -- couldn't that cause exactly the sort of situation
> though where stability of statement is violated?

It shouldn't...

The data gets stored physically, on disk, in a canonical form.

Why should it be "unstable" to capture data in a canonical form, when
that's what gets stored on disk?
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