Heikki,
> It's important to distinguish what kind of fadvise we're talking about.
> The bitmap scan code issues hints about individual pages, using
> posix_fadvise(... POSIX_FADV_WILLNEED). For increasing the readahead of
> a sequential scan, you'd want to use POSIX_FADV_SEQUENTIAL. I believe
> the support for the latter is much more widespread than for the former.
OK, so this is potentially useful (pending testing) but it's a different
feature. We'll discuss it for 8.5.
The other thing I was going to ask you about is using posix_fadvise as
an alternative to O_DIRECT for the xlog. O_DIRECT is, AFAIK,
linux-only, whereas there are "direct write" fadvise flags which work on
multiple OSes.
--
Josh Berkus
PostgreSQL Experts Inc.
www.pgexperts.com