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Re: Losing memory references - SRF + SPI - Mailing list pgsql-hackers

From Anderson Carniel
Subject Re: Losing memory references - SRF + SPI
Date
Msg-id CAAAXyN1L1E4UANe4oEMU8ThE9qLVOxQcaAKS1C+_uyn-J7MzZg@mail.gmail.com
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In response to Re: Losing memory references - SRF + SPI  (Joe Conway <mail@joeconway.com>)
Responses Re: Losing memory references - SRF + SPI  (Michael Paquier <michael.paquier@gmail.com>)
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Thank you very much Joe. 

I have followed the crosstab() implementation and understood the idea of per query memory context. Now, I am using a unique SPI instance (which I perform several sql queries), process the result, transform my result into a tuplestore, close the SPI and done. It works perfectly. 

I have a curiosity with regard to the tuplestore: is there a problem with performance if my tuplestore form a big table with million of tuples? Other question is regarding to SPI: is there a problem to use only  one instance of SPI (for instance, if multiple users call the same function)?

Thank you again,
Anderson Carniel

2016-05-14 12:19 GMT-03:00 Joe Conway <mail@joeconway.com>:
On 05/13/2016 09:35 PM, Anderson Carniel wrote:
> I am writing a function that returns a set of tuples by using also the
> PostGIS. Thuis, I am using SRF too. It successfully returns the expected
> result when it has at most 4 tuples. However, this is not the case when
> more than 4 tuples have to be returned. When I debug the code, I found
> that the problem is in my function that transforms a cstring after a
> SPI_connection. It seems that this cstring is not valid anymore in the
> moment of this conversion (see my comment below). I know that the SPI
> uses different contexts when it init and finish its process. But, I
> don't understand why I have this problem here. Please, note that I tried
> to copy the values of the whole tuple, but I have the same problem:
> system crash after the forth call of the function. Also note that I call
> this function only in the init call of the SRF. Please I would
> appreciate any suggestion and help.

You probably need to allocate your returned values in a per query memory
context. Take a look at how it is done in, for example, crosstab() in
contrib/tablefunc.

HTH,

Joe

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