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Number   :  2599
Date     :  2002-08-04
Author   :  Kan Yabumoto
Subject  :  The Last-Access timestamp
Size(KB) :  3


I just posted an answer to Tom who asked a question
for XXCOPY command line which deletes files that have
not been accessed in the past 730 days.

xxcopy xxcopy \src\ /rs/db#731/fa

/DB#731 // on or before 731 days ago
/FA // filedate using the Last Access value.

Even though Microsoft introduced the concept of
the Creation time and the Last Access time in addition
to the Last Write (modify) time like in Unix,
Microsoft failed to educate the programming community at
large (including their own programmers at Microsoft)
as to how to administer this timestamp value.

As a result, there are so many programs that ignore
the last-access timestamp, or more precisely, most
programmers do not know how to follow the programming
procedures in order to make the Last Access timestamp
to be useful.

For example, in order for the Last Access timestamp to
be useful at all, certain file-copy programs which access
the contents of a file (e.g., read-access) should not let
the file system update the timestamp.

For example, When you have the MYRESUME.DOC file in a
directory, and if you access the file using Microsoft Word
and read the file contents, you want the incident to be
treated as a legitimate access which should be recorded by
updating the last-access value. On the other hand, when
you backup the file into some other directory for the
sake of making sure the file is stored elsewhere,
the backup operation itself (even though it involves a read
access of the file contents, --- not just looking at
the directory info for the file, or open without read
access) should not be considered as a legitimate access
which would trigger the timestamp update.

That restricts very severely on which file-copy programs
(and which file-maintenance utilities for various jobs)
to use in order to do any access of the file contents.
For example, if you use the Windows Explorer (by drag and
drop) to copy the file, the operation constitute a
read access, and therefore, the system will record it
as the Last Access. Similarly, if you use the COPY
command of the Windows, you will find the timestamp for
the Last Access modified.

As far as we know, there are only a few file-copy
programs that preserves the Last Access timestamp
(if a file-access program does not do any particular
action with regard to the Last Access timestamp,
the default behavior of the file system is to
record the access as the Last Access).

The MS Backup program is one such a program which
"preserves" the LastAccess timestamp.

BTW, XXCOPY does not modify the LastAccess timestamp
(unless you force it to modify it by /TTA).

How about system tools such as the GREP utility which
opens files and reads the contents (which is an *ACCESS*
as far as the file system is concerned)? If you scan
a directory using GREP in search of some word, all the
files the directory will receive a new "Last-Access"
timestamp, unless the GREP program is aware of the
implication and explicitly preserves the LastAccess
value (I doubt most GREP utilities do this), the time-
stamp will become quite useless.

In other words, unless you discipline yourself to
always use those LastAccess-preserving file management
tools to copy the files (such as MS-BACKUP and XXCOPY),
the LastAccess timestamp gets updated so often,
the goal you are trying to achieve by removing those
inactive files will likely disappoint you.

As far as I'm concerned, the LastAccess timestamp
is nearly useless.

Kan Yabumoto



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