Re: Cost estimation in foreign data wrappers

Hadi Moshayedi <hadi(at)moshayedi(dot)net> writes:
> There is a callback function in fdw's which should also set estimates for
> startup and total costs for each path. Assume a fdw adds only one path
> (e.g. in file_fdw). I am trying to understand what can go wrong if we do a
> bad job in estimating these costs.

> Since we have only one scan path here, it doesn't make a difference in
> choosing the best scan path.

Right. But if there's more than one table in the query, it might make a
difference in terms of what join plan gets chosen. I'd say that getting
an accurate rowcount estimate is usually far more important, though.

regards, tom lane