On Thu, Mar 10, 2022 at 7:46 PM Andres Freund <andres@anarazel.de> wrote:
> I'm not talking about just moving the vistest acquisition, but also
> vacuum_set_xid_limits(). Which obviously *does* benefit from delaying as long
> as possible.
That sounds hard, or at least a lot of work given the benefits.
As the patch points out, we are required to establish rel_pages after
we have established OldestXmin. We *also* use rel_pages to determine
the size of the dead_items array -- we don't want to allocate space
that couldn't possibly be used (i.e. a dead_items array with room for
more than `MaxHeapTuplesPerPage * rel_pages` dead items in total).
In short, it will be necessary to break that dependency, somehow.
Which is possibly, certainly, but still quite messy.
--
Peter Geoghegan
