TODO item not needed anymore now that the buffer cache is

scan-resistant:

<
< * Allow free-behind capability for large sequential scans, perhaps using
<   posix_fadvise()
<
<   Posix_fadvise() can control both sequential/random file caching and
<   free-behind behavior, but it is unclear how the setting affects other
<   backends that also have the file open, and the feature is not supported
<   on all operating systems.