On 2014-12-09 14:41:46 -0300, Alvaro Herrera wrote:
> So I've been updating my very old patch to allow logical and physical
> column reordering. Here's a WIP first cut for examination.
Do you have a updated patch that has ripened further?
> The first thing where this matters is tuple descriptor expansion in
> parse analysis; at this stage, things such as "*" (in "select *") are
> turned into a target list, which must be sorted according to attlognum.
> To achieve this I added a new routine to tupledescs,
> TupleDescGetSortedAttrs() which computes a new Attribute array and
> caches it in the TupleDesc for later uses; this array points to the
> same elements in the normal attribute list but is order by attlognum.
That sounds sane.
> Another place that needs tweaking is heapam.c, which must construct a
> physical tuple from Datum/nulls arrays (heap_form_tuple). In some cases
> the input arrays are sorted in logical column order.
I'm not sure that changing heaptuple.c's API (you mean that, not
heapam.c, right?) is a good level to tackle this at. I think some
function to reorder values/isnull arrays into logical order and reverse
might end up being less invasive and actually faster.
Greetings,
Andres Freund