Just eyeing the code ... another thing we changed since 8.3 is to enable
posix_fadvise() calls for WAL. Any of the complaints want to try diking
out this bit of code (near line 2580 in src/backend/access/transam/xlog.c)?
#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
if (!XLogArchivingActive() &&
(get_sync_bit(sync_method) & PG_O_DIRECT) == 0)
(void) posix_fadvise(openLogFile, 0, 0, POSIX_FADV_DONTNEED);
#endif
regards, tom lane