On Mon, 17 May 2021 at 00:11, Tatsuo Ishii <is...@sraoss.co.jp> wrote: > I think there is a typo in src/backend/storage/lmgr/README.barrier. > Attached patch should fix it.
Yeah looks like a typo to me. I wonder if we also need to fix this part: > either one does their writes. Eventually we might be able to use an atomic > fetch-and-add instruction for this specific case on architectures that support > it, but we can't rely on that being available everywhere, and we currently > have no support for it at all. Use a lock. That seems to have been written at a time before we got atomics. The following also might want to mention atomics too: > 2. Eight-byte loads and stores aren't necessarily atomic. We assume in > various places in the source code that an aligned four-byte load or store is > atomic, and that other processes therefore won't see a half-set value. > Sadly, the same can't be said for eight-byte value: on some platforms, an > aligned eight-byte load or store will generate two four-byte operations. If > you need an atomic eight-byte read or write, you must make it atomic with a > lock. David
