Re: copy vs. C function

On Wed, Dec 14, 2011 at 9:40 AM, Jon Nelson <jnelson+pgsql(at)jamponi(dot)net> wrote:
> On Wed, Dec 14, 2011 at 9:25 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Jon Nelson <jnelson+pgsql(at)jamponi(dot)net> writes:
>>> Regarding caching, I tried caching it across calls by making the
>>> TupleDesc static and only initializing it once.
>>> When I tried that, I got:
>>
>>> ERROR:  number of columns (6769856) exceeds limit (1664)
>>
>>> I tried to find some documentation or examples that cache the
>>> information, but couldn't find any.
>>
>> You might find reading record_in to be helpful.  What it caches is not
>> exactly what you need to, I think, but it shows the general principles.
>> There are lots of other functions that use fn_extra to cache info, too.
>
> I will definitely look into those. I'm probably doing it wrong, but in
> the meantime, I allocated enough space (by way of MemoryContextAlloc)
> in TopMemoryContext for an AttInMetadata pointer, switched to that
> memory context (just the first time through), used CreateTupleDescCopy
> + TupleDescGetAttInMetadata to duplicate (in the new memory context)
> the TupleDesc, and then switched back. This approach seems to have
> dropped the total run time to about 54 seconds, the bulk of which is
> BuildTupleFromCStrings, a rather significant improvement.
>
> ....
>
> Looking at record_in, I think I see what I could be doing better.

Indeed. I revised the code to make use of fcinfo->flinfo->fn_extra for
storage and fcinfo->flinfo->fn_mcxt for the MemoryContext and
everything seemed to work just fine.

Assuming one *starts* with a char *some_var[8], would building Datum
myself be faster than using BuildTupleFromCStrings?

--
Jon