> What you really want is Solaris's free-behind, where it detects if a
> scan is exceeding a certain percentage of the OS cache and moves the
> pages to the _front_ of the to-be-reused list.  I am not sure what
> other OS's support this, but we need this on our own buffer manager
> code as well.
> Our TODO already has:
>       * Add free-behind capability for large sequential scans (Bruce)
> Basically, I think we need free-behind rather than O_DIRECT.

I suppose, but you've already polluted the cache by the time the above
mentioned mechanism kicks in and takes effect.  Given that the planner
has an idea of how much data it's going to read in in order to
complete the query, seems easier/better to mark the fd O_DIRECT.


Sean Chittenden

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