Re: Two different defs of MAX_TUPLES_PER_PAGE

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> #define MAX_TUPLES_PER_PAGE ((BLCKSZ - 1) / (MAXALIGN(offsetof(HeapTupleHeaderData, t_bits)) + sizeof(ItemIdData)) + 1)
> (I believe that both modules want a ceiling definition not a floor
> definition, ie round up any fraction. The -1 / +1 trick is of course
> just one way to get that.)

Don't you think about PageHeaderData? Also I guess a floor definition is ok
because 'number of tuples' is an integer. How about the following?

((BLCKSZ - offsetof(PageHeaderData, pd_linp)) /
(MAXALIGN(offsetof(HeapTupleHeaderData, t_bits)) + sizeof(ItemIdData)))

> Also, is this something that should be in a common header file? If so
> which one? BLCKSZ, HeapTupleHeaderData, and ItemIdData are all defined
> in different places ...

Considering include-hierarchy, I think bufpage.h is a good place.

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ITAGAKI Takahiro
NTT Cyber Space Laboratories