Message-ID: <50EFF145.1050306@vmware.com>
Date: Fri, 11 Jan 2013 13:02:29 +0200
From: Heikki Linnakangas <hlinnakangas@vmware.com>
Organization: VMware
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To: Matheus de Oliveira <matioli.matheus@gmail.com>
CC: pgsql-performance <pgsql-performance@postgresql.org>,
	Charles Gomes <charlesrg@outlook.com>
Subject: Re: Partition insert trigger using C language
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On 11.01.2013 12:36, Matheus de Oliveira wrote:
> On Fri, Jan 11, 2013 at 8:19 AM, Heikki Linnakangas<hlinnakangas@vmware.com
>> wrote:
>
>> One thing that caught my eye:
>>
>>   CREATE OR REPLACE FUNCTION partition_insert_trigger_spi()
>>> RETURNS trigger
>>> LANGUAGE C
>>> VOLATILE STRICT
>>> AS 'partition_insert_trigger_spi'**,'partition_insert_trigger_**spi'
>>> SET DateStyle TO 'ISO';
>>
>> Calling a function with SET options has a fair amount of overhead, to
>> set/restore the GUC on every invocation. That should be avoided in a
>> performance critical function like this.
>
> I (stupidly) used SPI_getvalue [1] and expected it to always return as
> YYYY-MM-DD, but them I remembered it would do that only with DateStyle=ISO.
>
> But the truth is that I couldn't see any overhead, because the function was
> without that on my first tests, and after that I saw no difference on the
> tests.

Oh, ok then. I would've expected it to make a measurable difference.

> I think I should use SPI_getbinvalue instead, but I don't know how
> to parse the result to get year and month, any help on that?

The fastest way is probably to use j2date like date_out does:

   DateADT		date = DatumGetDateADT(x)
   int year, month, mday;

   if (DATE_NOT_FINITE(date))
	elog(ERROR, "date must be finite");
   j2date(date + POSTGRES_EPOCH_JDATE, &year, &month, &mday);

- Heikki


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