Re: a bit more precise MaxOffsetNumber

2011/4/30 Tomas Vondra <tv(at)fuzzy(dot)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
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