[HACKERS] pgstattuple documentation clarification

Recently a client was confused because there was a substantial 
difference between the reported table_len of a table and the sum of the 
corresponding tuple_len, dead_tuple_len and free_space. The docs are 
fairly silent on this point, and I agree that in the absence of 
explanation it is confusing, so I propose that we add a clarification 
note along the lines of:

   The table_len will always be greater than the sum of the tuple_len,   dead_tuple_len and free_space. The difference is accounted for by   page overhead and space that is not free but cannot be attributed to   any particular tuple.


Or perhaps we should be more explicit and refer to the item pointers on 
the page.


Thoughts?


cheers


andrew