> AFAICS, making them exact would not improve the planning estimates
> at all, because there are too many other sources of error. We have
> approximate stats already via vacuum/analyze statistics gathering.
> >>
> What happens if someone deletes 75% of a table?
> What happens if someone imports 30 times more rows than are already in
> the table?
> What happens if one table is remarkably small or even empty and you are
> unaware?
If you are unaware of any of the above, you'll get poorer performance.
Just make sure you run ANALYZE often enough. Anyone who does a massive
change in the number of rows in a table, or updates most of a table should
always do an ANALYZE afterwards.
Chris