file read dates

[Roy Smith]

In article <183 at magic.ARPA> stewart at magic.ARPA (Larry Stewart) writes:
> Who looks at file read dates?  Do any more-or-less standard Unix
> applications look at them?  Are they worth the trouble of maintaining?

	We use read times for man page cacheing.  On 4.2bsd (and others?)
the nroff source files for the manual pages are kept in /usr/man/man?/*,
with the formated files in /usr/man/cat?/*.  When you ask for a man page,
man shows you the cat file.  If it is missing or out of date w.r.t. the
nroff source, man creates it.

	 I have a line in /usr/lib/crontab that finds and removes files in
/usr/man/cat?/ that havn't been accessed in 14 days.  This strikes a good
balance between having all the man pages pre-formated (i.e. eating disk
space) and having nroff run every time somebody runs man (sooo sloooow).  I
don't care when the man page was formated; as long as somebody reads it
every other week, it stays around.

	Many big OS's implement a migrate-to-tape scheme.  Files which are
not accessed in a certain amount of time are automatically moved from the
main system store (i.e. disk) to some other (larger, cheaper, slower)
device and a marker left telling where the file went.  To implement this on
Unix would be fairly easy using file access times.  This was discussed a
few (6-12?) months ago in net.unix-wizards, I think.

	As an aside, note that this backup store might be tape, requiring
manual intervention to retrieve files, or it might be something else.  I
understand that there are large (many Gbyte) mass storage devices available
(from IBM?) with access times on the order of minutes.
-- 
Roy Smith <allegra!phri!roy>
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016