This is wrt Postgres 8.4 beta1 which has a new effective_io_concurrency tunable which uses posix_fadvice http://www.postgresql.org/docs/8.4/static/runtime-config-resource.html (Go to the bottom) Quote: synchronous I/O depends on an effective |posix_fadvise| function, which some operating systems lack. If the function is not present then setting this parameter to anything but zero will result in an error. On some operating systems the function is present but does not actually do anything (e.g. Solaris). I am trying to understand if posix_fadvise is useful on ZFS or not? Currently postgres now does not do any fadvise on OpenSolaris since ZFS ignores the advise (after all who takes advise) without letting the app know that it is being ignored. On Linux it uses the POSIX_FADV_WILLNEED flag (example shown below) http://doxygen.postgresql.org/fd_8c-source.html#l01054 But in general I am trying to figure out few things: 1. Is it even worth doing posix_fadvise on zfs 2. How does it impact UFS 3. What should be the equivalent workarounds for zfs and/or UFS? Thanks in advance regards Jignesh -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20090421/d239bda7/attachment.html>
This is wrt Postgres 8.4 beta1 which has a new effective_io_concurrency tunable which uses posix_fadvice http://www.postgresql.org/docs/8.4/static/runtime-config-resource.html (Go to the bottom) Quote: synchronous I/O depends on an effective |posix_fadvise| function, which some operating systems lack. If the function is not present then setting this parameter to anything but zero will result in an error. On some operating systems the function is present but does not actually do anything (e.g. Solaris). I am trying to understand if posix_fadvise is useful on ZFS or not? Currently postgres now does not do any fadvise on OpenSolaris since ZFS ignores the advise (after all who takes advise) without letting the app know that it is being ignored. On Linux it uses the POSIX_FADV_WILLNEED flag (example shown below) http://doxygen.postgresql.org/fd_8c-source.html#l01054 But in general I am trying to figure out few things: 1. Is it even worth doing posix_fadvise on zfs 2. How does it impact UFS 3. What should be the equivalent workarounds for zfs and/or UFS? Thanks in advance regards Jignesh -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.opensolaris.org/pipermail/zfs-discuss/attachments/20090422/a3ef62a0/attachment.html>