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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: news.software.b
Subject: Re: Why does rnews duplicate its history?
Message-ID: <8530@utzoo.UUCP>
Date: Mon, 31-Aug-87 16:06:56 EDT
Article-I.D.: utzoo.8530
Posted: Mon Aug 31 16:06:56 1987
Date-Received: Mon, 31-Aug-87 16:06:56 EDT
References: <125@minya.UUCP>
Organization: U of Toronto Zoology
Lines: 27
Keywords: news history

> Say, I was wondering if anyone out there could explain something that
> has had me puzzled for a while.  Usenet has, as well known, this "history"
> file, and in addition, on this Sys/V machine, it has a history.d directory
> that contains files 0 thru 9.  Each of these is a subset of "history"...
> However, the software as compiled here insists on keeping *both* the
> large history file and the 10 little ones.  This strikes me as a bit
> on the bizarre side.  I mean, isn't that getting the worst of both
> worlds? ...

What you're seeing is a SysV emulation of something that makes a bit more
sense in non-SysV Unixes.  In the non-SysV world, there's a little library
called "dbm" which lets one maintain sort of a symbol table.  The point of
this is that news can use dbm to find out *quickly* whether an article with
a given message-id exists on the system already.  Using dbm is *much much*
faster than scanning the whole history file, especially in non-SysV systems
that historically have rather slow implementations of fgets.  The history
file provides the authoritative record; dbm's role is to provide fast access.
It's worth the price of having to keep both up to date. 

Unfortunately, there's no dbm in SysV, so it was faked.  I don't know whether
anybody looked carefully at the tradeoffs in SysV, although the 0-9 split
should be cutting search overhead noticeably.  The point is that it's not
really a duplication of effort -- the main history file and its subsidiaries
are specialized for different uses.
-- 
"There's a lot more to do in space   |  Henry Spencer @ U of Toronto Zoology
than sending people to Mars." --Bova | {allegra,ihnp4,decvax,utai}!utzoo!henry