Re: Import Statistics in postgres_fdw before resorting to sampling.

Other initial comments:

The commit message says:

    This is managed via two new options, fetch_stats and remote_analyze,
    both are available at the server level and table level. If fetch_stats
    is true, then the ANALYZE command will first attempt to fetch statistics
    from the remote table and import those statistics locally.

    If remote_analyze is true, and if the first attempt to fetch remote
    statistics found no attribute statistics, then an attempt will be made
    to ANALYZE the remote table before a second and final attempt to fetch
    remote statistics.

    If no statistics are found, then ANALYZE will fall back to the normal
    behavior of sampling and local analysis.

I think the first step assumes that the remote stats are up-to-date;
if they aren't, it would cause a regression.  (If the remote relation
is a plain table, they are likely to be up-to-date, but for example,
if it is a foreign table, it's possible that they are stale.)  So how
about making it the user's responsibility to make them up-to-date?  If
doing so, we wouldn't need to do the second and third steps anymore,
making the patch simple.

On the other hand:

    This operation will only work on remote relations that can have stored
    statistics: tables, partitioned tables, and materialized views. If the
    remote relation is a view then remote fetching/analyzing is just wasted
    effort and the user is better of setting fetch_stats to false for that
    table.

I'm not sure the waste effort is acceptable; IMO, if the remote table
is a view, I think that the system should detect that in some way, and
then just do the normal ANALYZE processing.

That's it for now.

My apologies for the delayed response.