Virender Singla <virender.cse@gmail.com> writes:
> Why do Toast tables have it's own visibility map and xmin, xmax columns etc?
> Isn't it increasing row size in a toast table and adding more complexity?
There are advantages to having the same low-level format for toast tables
as regular tables --- for example, that you can look into a toast table
for debugging purposes with normal SQL queries. Even if we weren't tied
to that format for disk-storage-compatibility reasons, I'd be disinclined
to change it.
It might be feasible to drop the visibility map for toast tables, though.
I agree that's not buying much, since ordinary queries don't consult it.
Not sure if there'd be a win proportional to the added code complexity.
regards, tom lane