Re: Question on alignment

Antonin Houska <ah(at)cybertec(dot)at> wrote:

> Since palloc() only ensures MAXIMUM_ALIGNOF, that wouldn't help here anyway.

After some more search I'm not sure about that. The following comment
indicates that MAXALIGN helps too:

/*
* Use this, not "char buf[BLCKSZ]", to declare a field or local variable
* holding a page buffer, if that page might be accessed as a page and not
* just a string of bytes. Otherwise the variable might be under-aligned,
* causing problems on alignment-picky hardware. (In some places, we use
* this to declare buffers even though we only pass them to read() and
* write(), because copying to/from aligned buffers is usually faster than
* using unaligned buffers.) We include both "double" and "int64" in the
* union to ensure that the compiler knows the value must be MAXALIGN'ed
* (cf. configure's computation of MAXIMUM_ALIGNOF).
*/
typedef union PGAlignedBlock
{
char data[BLCKSZ];
double force_align_d;
int64 force_align_i64;
} PGAlignedBlock;

--
Antonin Houska
Web: https://www.cybertec-postgresql.com