On Fri, Oct 9, 2020 at 5:40 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> > Looking a bit deeper into this, I'm wondering if in fact your
> > EstimateStringSize() and EstimateNodeSize() functions should be using
> > BUFFERALIGN() for EACH stored string/node (rather than just calling
> > shm_toc_estimate_chunk() once at the end, after the length of packed
> > strings and nodes has been estimated), to ensure alignment of start of
> > each string/node. Other Postgres code appears to be aligning each
> > stored chunk using shm_toc_estimate_chunk(). See the definition of
> > that macro and its current usages.
> >
>
> I am not sure if this required for the purpose of correctness. AFAIU,
> we do store/estimate multiple parameters in same way at other places,
> see EstimateParamListSpace and SerializeParamList. Do you have
> something else in mind?
>
The point I was trying to make is that potentially more efficient code
can be used if the individual strings/nodes are aligned, rather than
packed (as they are now), but as you point out, there are already
cases (e.g. SerializeParamList) where within the separately-aligned
chunks the data is not aligned, so maybe not a big deal. Oh well,
without alignment, that means use of memcpy() cannot really be avoided
here for serializing/de-serializing ints etc., let's hope the compiler
optimizes it as best it can.
Regards,
Greg Nancarrow
Fujitsu Australia