Hi,
On 2021-04-21 17:38:53 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > I don't really see us getting rid of something like ctid as a generic
> > concept across AMs - there's just too many places that need a way to
> > reference a specific tuple. However, I think we ought to change how much
> > code outside of AMs know about what tids mean. And, although that's a
> > significant lift on its own, we ought to make at least the generic
> > representation variable width.
>
> It seems like it might not be that hard to convert ctid generically
> into a uint64, where heaps and heap-related indexes only use 6 bytes
> of it.
Yep.
> Variable-width I agree would be a very big complication added on top,
> and I'm not quite convinced that we need it.
I can see three (related) major cases where variable width tids would be
quite useful:
1) Creating an index-oriented-table AM would harder/more
limited with just an 8 byte tid
2) Supporting "indirect" indexes (i.e. indexes pointing to a primary
key, thereby being much cheaper to maintain when there are updates),
would require the primary key to map to an 8 byte integer.
3) Global indexes would be a lot easier if we had variable width tids
(but other ways of addressing the issue are possible).
Greetings,
Andres Freund
