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
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