Steve Pritchard <steve(dot)pritchard(at)bto(dot)org> writes:
> -- Average length of a row in bytes:
> select avg(octet_length(t.*::text)) FROM observation t;
> -- 287 bytes
That measurement technique doesn't have a lot to do with reality,
I'm afraid.
The contrib/pgstattuple module could give you a more reliable idea of
how much space is in use or not in the table.
regards, tom lane