Re: [HACKERS] Aggregates with context - a question

At 10:20 9/06/99 -0400, Tom Lane wrote:

>> This is clearly not the case, and I have declared them as int4, which
>> will also presumable break on 64 bit implementations...
>
>The "clean" way to do it is to make a declared datatype that corresponds
>to the state storage you need, but that's overkill if such a datatype
>hasn't got any other use. I think the way you have done it is a
>reasonable cheat, though I agree that using int4 is risky for
>portability. There has been some talk of inventing a type OID
>representing "C string", and that (when available) might be a better way
>of declaring transtype1 when it's really a private struct of some sort.

Sounds like a wonderful idea; does this mean that users can be prevented from declaring a column of type 'C String'? Or do you then need to build all the support functions? I suppose the alternative would be to use a 'varbinary' (or varchar?), which has the first word being the structure length. That would at least be standard.

>One thing you have to be very careful about is memory allocation and
>lifetime. The way you are doing it, a palloc in the first transfn1
>iteration and a pfree in finalfn, will be fine. However this may change
>in 6.6, since we are going to have to do something to cure memory leaks
>in aggregation. (Currently, if the transfns are ones that palloc their
>result value, as all float8 ops do for example, the storage is not
>reclaimed until end of transaction. That's no good if there are lots of
>tuples...)
>
>> Anyway, the code is below.
>
>Looks OK except you are potentially pfreeing an uninit pointer in the
>finalfn...
>

Oops - pretty clever, considering I had already checked if it was zero...

Thanks for the information,

Philip

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