Re: final patch - plpgsql: for-in-array

2010/11/18 Cédric Villemain <cedric(dot)villemain(dot)debian(at)gmail(dot)com>:
> 2010/11/18 Robert Haas <robertmhaas(at)gmail(dot)com>:
>> On Thu, Nov 18, 2010 at 10:24 AM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
>>> On Thu, Nov 18, 2010 at 12:47 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>>> Merlin Moncure <mmoncure(at)gmail(dot)com> writes:
>>>>> On Wed, Nov 17, 2010 at 7:08 PM, Jaime Casanova <jaime(at)2ndquadrant(dot)com> wrote:
>>>>>> i will start the review of this one... but before that sorry for
>>>>>> suggesting this a bit later but about using UNNEST as part of the
>>>>>> sintax?
>>>>
>>>>> Does for-in-array do what unnset does?
>>>>
>>>> Yes, which begs the question of why bother at all.  AFAICS this patch
>>>> simply allows you to replace
>>>>
>>>>        for x in select unnest(array_value) loop
>>>>
>>>> with
>>>>
>>>>        for x in unnest array_value loop
>>>>
>>>> (plus or minus a parenthesis or so).  I do not think we need to add a
>>>> bunch of code and create even more syntactic ambiguity (FOR loops are
>>>> already on the hairy edge of unparsability) to save people from writing
>>>> "select".
>>>
>>> Pavel's performance argument is imnsho valid. arrays at present are
>>> the best way to pass data around functions and any optimizations here
>>> are very welcome.  Given that, is there any way to mitigate your
>>> concerns on the syntax side?
>>
>> Can we get the performance benefit any other way?  I hate to think
>> that it will still be slow for people using the already-supported
>> syntax.
>
> If you are able to make unnest() outputting 1st row without detoasting
> last field.
>
> I think if we have :
> #define DatumGetTextPSlice(X,m,n)   ((text *) PG_DETOAST_DATUM_SLICE(X,m,n))
> but for array, most is done
>
> Pavel, am I correct ?

yes, it can help, but still if you iterate over complete array, you
have to do n - detoast ops.

Pavel

>
>>
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>> Robert Haas
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> Cédric Villemain               2ndQuadrant
> http://2ndQuadrant.fr/     PostgreSQL : Expertise, Formation et Support
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