2011/4/30 Tomas Vondra <tv@fuzzy.cz>:
> I've been digging in the sources, and I've noticed the MaxOffsetNumber
> is defined (in storage/off.h) like this
>
> (BLCKSZ / sizeof(ItemIdData))
>
> I guess it might be made a bit more precise by subtracting the header
> like this
>
> (BLCKSZ - offsetof(PageHeaderData, pd_linp) / sizeof(ItemIdData))
>
> although the difference is negligible (2048 vs 2042 for 8kB pages).
I guess we could do that, but I'm not sure there's much point. It's
also not entirely clear that this would actually work out to a win,
because of the issues discussed in the "When can/should we prune or
defragment?" section of src/backend/access/heap/README.HOT
We could probably figure this out with some careful testing, but I'm
not sure it's worth the effort.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
