Robert Haas <robertmhaas@gmail.com> writes:
> I'm just talking out of my rear end here because I don't know what the
> real numbers are, but it's far from obvious to me that there's any
> free lunch here. That having been said, just because indexing
> relfilenode or adding relfilenodes to WAL records is expensive doesn't
> mean we shouldn't do it. But I think we need to know the price tag
> before we can judge whether to make the purchase.
Certainly, any of these solutions are going to cost us somewhere ---
either up-front cost or more expensive (and less reliable?) changeset
extraction, take your choice. I will note that somehow tablespaces got
put in despite having to add 4 bytes to every WAL record for that
feature, which was probably of less use than logical changeset
extraction will be.
But to tell the truth, I'm mostly exercised about the non-unique
syscache. I think that's simply a *bad* idea.
regards, tom lane