It can save space because the line pointers have less alignment
requirements. But I don't see any point in the current state.
--
Greg
On 2009-12-04, at 3:48 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Greg Stark <gsstark@mit.edu> writes:
>> I'm not sure why I said "including ctid". We would have to move
>> everything transactional to the line pointer, including xmin, xmax,
>> ctid, all the hint bits, the updated flags, hot flags, etc. The only
>> things left in the tuple header would be things that have to be there
>> such as HAS_OIDS, HAS_NULLS, natts, hoff, etc. It would be a pretty
>> drastic change, though a fairly logical one. I recall someone
>> actually
>> submitted a patch to separate out the transactional bits anyways a
>> while back, just to save a few bytes in in-memory tuples. If we could
>> save on disk-space usage it would be a lot more compelling. But it
>> doesn't look to me like it really saves enough often enough to be
>> worth so much code churn.
>
> It would also break things for indexes, which don't need all that
> stuff
> in their line pointers.
>
> More to the point, moving the same bits to someplace else on the page
> doesn't save anything at all.
>
> regards, tom lane