tmp, 20.01.2010 11:25:
>> http://www.postgresql.org/docs/8.4/static/storage-page-layout.html
>
> I fail to find the size of the *row* header on that link.
>
"All table rows are structured in the same way. There is a fixed-size header (occupying 23 bytes on most machines), followed by an optional null bitmap, an optional object ID field, and the user data. The header is detailed in Table 53-4."
http://www.postgresql.org/docs/8.4/static/storage-page-layout.html#HEAPTUPLEHEADERDATA-TABLE