On 2014-09-11 11:39:12 -0400, Tom Lane wrote: > Even on Intel, I'd wonder what unaligned accesses do to atomicity > guarantees and suchlike.
They pretty much kill atomicity guarantees. Atomicity is guaranteed while you're inside a cacheline, but not once you span them. > This is not a big deal for row data storage, > but we'd have to be careful about it if we were to back off alignment > requirements for in-memory data structures such as latches and buffer > headers. Right. I don't think that's an option. > Another fun thing you'd need to deal with is ensuring that the C structs > we overlay onto catalog data rows still match up with the data layout > rules. Yea, this would require some nastyness in the bki generation, but it'd probably doable to have different alignment for system catalogs. > On the whole, I'm pretty darn skeptical that such an effort would repay > itself. There are lots of more promising things to hack on. I have no desire to hack on it, but I can understand the desire to reduce the space overhead... Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
