Re: [PATCH] Generalized JSON output functions

On Fri, Jul 10, 2015 at 4:04 PM, Pavel Stehule <pavel.stehule@gmail.com> wrote:

 

2. why you did indirect call via JsonOutContext?

What is benefit

dst.value(&dst, (Datum) 0, JSONTYPE_NULL, InvalidOid, InvalidOid, false);

instead

json_out_value(&dst, ....)

For consistency.  Even though we initialize the output context ourselves, there might be some code introduced between json_out_init_context() and dst.value() calls that replaces some of the callbacks, and then there would be a difference.

 

with this consistency? I didn't see this style everywhere in Postgres?  Isn't it premature optimization?

 

Well, one could call it premature pessimization due to dynamic call overhead.

IMO, the fact that json_out_init_context() sets the value callback to json_out_value is an implementation detail, the other parts of code should not rely on.  And for the Explain output, there definitely going to be *some* code between context initialization and output callbacks: these are done in a number of different functions.

--

Alex