Re: Variable length varlena headers redux

Greg Stark wrote:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>
> > > So (nigh) every tuple will get deformed and reformed once before it goes to
> > > disk? Currently the toast code doesn't even look at a tuple if it's small
> > > enough, but in this case we would want it to fire even on very narrow rows.
> >
> > I'd be inclined to put the intelligence into heap_form_tuple and thereby
> > avoid getting the TOAST code involved unless there are wide fields to
> > deal with.
>
> And have heap_deform_tuple / heap_getattr palloc and memcpy the the datum on
> the way out? Or wait until detoast time and then do it?
>
> If we do it on the way out of the heaptuple then we could have a rule that
> headers are always compressed in a tuple and always uncompressed out of a
> tuple.
>
> But I'm surprised, I had the impression that you were reluctant to consider
> memcpying all the data all the time.

Uh, if the macros can read 1 and 4-byte headers, why do we need to
allocate memory for them?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com

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