Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> So the question is, do we take the overhead of the new index (which
> means overhead on DML operations -- supposedly rare) or do we take the
> overhead of larger WAL records (which means overhead on all DDL
> operations)?
> Note we can make either thing apply to only people running logical
> replication.
I don't believe you can have or not have an index on pg_class as easily
as all that. The choice would have to be frozen at initdb time, so
people would have to pay the overhead if they thought there was even a
small possibility that they'd want logical replication later.
Flipping the content of WAL records might not be a terribly simple thing
to do either, but at least in principle it could be done during a
postmaster restart, without initdb.
regards, tom lane