Alvaro Herrera <alvhe...@2ndquadrant.com> writes:
> I wonder if this is permissible and whether it will do the right thing
> on 32-bit systems:

> /*
>  * Special area of BRIN pages.
>  *
>  * We add some padding bytes to ensure that 'type' ends up in the last two
>  * bytes of the page, for consumption by pg_filedump and similar utilities.
>  * (Special space is MAXALIGN'ed).
>  */
> typedef struct BrinSpecialSpace
> {
>       char            padding[MAXALIGN(1) - 2 * sizeof(uint16)];
>       uint16          flags;
>       uint16          type;
> } BrinSpecialSpace;

I should expect that to fail altogether on 32-bit machines, because
the declared array size will be zero.

You could try something like

typedef struct BrinSpecialSpace
{
        uint16          vector[MAXALIGN(1) / sizeof(uint16)];
} BrinSpecialSpace;

and then some access macros to use the last and next-to-last
elements of that array.

                        regards, tom lane


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