Re: Batch insert in CTAS/MatView code

On 2019-Sep-25, Asim R P wrote:

> I reviewed your patch today.  It looks good overall.  My concern is that
> the ExecFetchSlotHeapTuple call does not seem appropriate.  In a generic
> place such as createas.c, we should be using generic tableam API only.
> However, I can also see that there is no better alternative.  We need to
> compute the size of accumulated tuples so far, in order to decide whether
> to stop accumulating tuples.  There is no convenient way to obtain the
> length of the tuple, given a slot.  How about making that decision solely
> based on number of tuples, so that we can avoid ExecFetchSlotHeapTuple call
> altogether?

... maybe we should add a new operation to slots, that returns the
(approximate?) size of a tuple?  That would make this easy.  (I'm not
sure however what to do about TOAST considerations -- is it size in
memory that we're worried about?)

Also:

+       myState->mi_slots_size >= 65535)

This magic number should be placed in a define next to the other one,
but I'm not sure that heapam.h is a good location, since surely this
applies to matviews in other table AMs too.