On Wed, Jul 6, 2022 at 12:27 PM Andres Freund <and...@anarazel.de> wrote: > I think my proposal of introducing a version of double that is marked to be 8 > byte aligned should do the trick as well, and doesn't have the problem of > changing the meaning of 'double' references in external headers. In fact, we > already have float8 as a type, so we could just add it there.
Yeah, but how easily will it be to know whether we've used that in every relevant place? Could we insist on 8-byte alignment even on 32-bit platforms? I think we have a few of those in the buildfarm, so maybe that would help us spot problems. Although I'm not sure how, exactly. > The problem with having a lot more alignment values is that it adds a bunch of > overhead to very performance critical paths. We don't want to add more > branches to att_align_nominal() if we can avoid it. Fair. > I'm fairly certain that we're going to add a lot more 64bit ints to catalogs > in the next few years, so this will become a bigger issue over time... Absolutely. > Outside of the catalogs I still think that we should work towards not aligning > byval values (and instead memcpy-ing the values to deal with alignment > sensitive platforms), so we don't waste so much space. And for catalogs we've > been talking about giving up the struct mapping as well, in the thread about > variable length names. In which case we could the cost of handling more > alignment values wouldn't be incurred as frequently. +1. Aligning stuff on disk appears to have few redeeming properties for the amount of pain it causes. -- Robert Haas EDB: http://www.enterprisedb.com
