Is there a reason we only use O_DIRECT with open_* sync options? xlogdefs.h says:
/* * Because O_DIRECT bypasses the kernel buffers, and because we never * read those buffers except during crash recovery, it is a win to use * it in all cases where we sync on each write(). We could allow O_DIRECT * with fsync(), but because skipping the kernel buffer forces writes out * quickly, it seems best just to use it for O_SYNC. It is hard to imagine * how fsync() could be a win for O_DIRECT compared to O_SYNC and O_DIRECT. * Also, O_DIRECT is never enough to force data to the drives, it merely * tries to bypass the kernel cache, so we still need O_SYNC or fsync(). */ This seems wrong because fsync() can win if there are two writes before the sync call. Can kernels not issue fsync() if the write was O_DIRECT? If that is the cause, we should document it. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
