... btw, I've not read this patch in any detail, but the recent thread
about toast tables for system catalogs prompts me to wonder what happens
if a "fast default" value is large enough to require out-of-line toasting.
I can easily think of problems that will ensue if we try to support that
case, because right now the toast mechanisms assume that OOL toasted
values can only be referenced from the associated table.
regards, tom lane