history - record of current and recently expired Usenet articles

     The file <config$_PATH_HISTORY> (typically /var/news/etc/history )  keeps
     a  record of all articles currently stored in the news system, as well as
     those that have been received but since expired.  In a typical production
     environment, this file will be many megabytes.

     The file consists of text lines.  Each line corresponds to  one  article.
     The  file  is  normally  kept  sorted  in the order in which articles are
     received, although this is not a requirement.  Innd(8) appends a new line
     each  time it files an article, and expire(8)  builds a new version of the
     file by removing old articles and purging old entries.

     Each line consists of two or three fields separated by a tab, shown below
     as \t:
          <Message-ID>   \t   date
          <Message-ID>   \t   date   \t   files

     The Message-ID field is the value of  the  article's  Message-ID  header,
     including the angle brackets.

     The date field consists of three sub-fields separated by  a  tilde.   All
     sub-fields are the text representation of the number of seconds since the
     epoch -- i.e., a time_t; see gettimeofday(2).  The first sub-field is the
     article's  arrival date.  If copies of the article are still present then
     the second sub-field is either the value of the article's Expires header,
     or  a hyphen if no expiration date was specified.  If an article has been
     expired then the second sub-field will be a hyphen.  The third  sub-field
     is the value of the article's Date header, recording when the article was

     The files field is a set of entries separated  by  one  or  more  spaces.
     Each  entry  consists  of  the  name  of  the newsgroup, a slash, and the
     article number.  This field is empty if the article has been expired.

     For  example,  an   article   cross-posted   to   comp.sources.unix   and
     comp.sources.d  that  was posted on February 10, 1991 (and received three
     minutes later), with an expiration date of May  5,  1991,  could  have  a
     history line (broken into two lines for display) like the following:
          <312@litchi.foo.com>  \t  666162000~673329600~666162180  \t
              comp.sources.unix/1104 comp.sources.d/7056

     In addition to the text file, there is a dbz(3z) database associated with
     the  file that uses the Message-ID field as a key to determine the offset
     in the text file  where  the  associated  line  begins.   For  historical
     reasons,  the  key  includes the trailing \0 byte (which is not stored in
     the text file).

     Written by Rich $alz  <rsalz@uunet.uu.net>  for  InterNetNews.   This  is
     revision 1.12, dated 1996/09/06.

     dbz(3z), expire(8) , innd(8) , news-recovery(8) .

You can find a summary and links related to this topic
as part of the Mib Software Usenet RKT.