Re: cache type info in json_agg and friends

On 09/14/2015 03:42 PM, Teodor Sigaev wrote:
>> Currently, json_agg, jsonb_agg, json_object_agg and jsonb_object_agg do
>> type classification on their arguments on each call to the transition
>> function. This is quite unnecessary, as the argument types won't change.
>> This patch remedies the defect by caching the necessary values in the
>> aggregate state object.
> +1
>
>>
>> While this doesn't change the performance much, since these functions
>> are essentially dominated by other bits of the processing, I think it is
>> nevertheless worth doing.
> Agree
>
> After quick observation of your patch, why don't you use FmgrInfo
> instead of JsonAggState.val_output_func/JsonAggState.key_category?
> FmgrInfo could be filled by fmgr_info_cxt() in aggcontext memory
> context. Suppose, direct usage of FmgrInfo with FunctionCall a bit
> faster than OidFunctionCall.

Well, we need the category to help data_to_json(b) do its work.
Nevertheless, it might be doable to pass an FmgrInfo* to datum_to_json.
I'll see what I can do.

cheers

andrew