Re: WIP: Covering + unique indexes.

31.03.2017 20:47, Andres Freund:

Maybe it would be better to modify index_form_tuple() to accept a new
argument with a number of attributes, then you can just Assert that
this number is never higher than the number of attributes in the
TupleDesc.

Good point.
I agree that this function is a bit strange. I have to set
tupdesc->nattrs to support compatibility with index_form_tuple().
I didn't want to add neither a new field to tupledesc nor a new
parameter to index_form_tuple(), because they are used widely.


But I haven't considered the possibility of index_form_tuple() failure.
Fixed in this version of the patch. Now it creates a copy of tupledesc to
pass it to index_form_tuple.

That seems like it'd actually be a noticeable increase in memory
allocator overhead.  I think we should just add (as just proposed in
separate thread), a _extended version of it that allows to specify the
number of columns.

The function is called not that often. Only once per page split for indexes with included columns.
Doesn't look like dramatic overhead. So I decided that a wrapper function would be more appropriate than refactoring of all index_form_tuple() calls.
But index_form_tuple_extended() looks like a better solution.

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Anastasia Lubennikova
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