At 11:56 AM -0700 1999/9/17, Matthew Dillon wrote:
> In real-life... for example, with a mail or web server, the namecache
> tends to be somewhat more effective then 50%. The web servers at BEST
> generally had a 95%+ name cache hit rate. The name cache misses are
> what are causing the lion's share of the directory inefficiencies.
Note that with a mail server, this is precisely the sort of thing
that happens with /var/spool/mqueue. In particular, with sendmail, a
qf/df pair of files get created, the message is received, the sender
is told "250 Ok", then sendmail goes to deliver the message in the
background, which 95-99% of the time happens on the first attempt,
and then the qf/df pair of files get deleted.
So, again, we see that they've actually done a decent first-pass
attempt at simulating the load a mail server would place on the
filesystem. All that we need to add now are a few more features. ;-)
With a news server using traditional spool, the file would tend
to get created, live for a relatively significant period of time
(days or even weeks before it gets expired), and only then would it
get removed.
An absolutely full newsfeed these days is running somewhere
around 1.1 million files comprising some 55GB of data (see
<http://transit.us-va.remarq.com/feed-size/>), or an average of
52,608.71 bytes per article. A very busy mail server might do a
million messages per day (or more), but the average message size
would be much closer to 2-5KB.
The primary difference between mail and news is that news
articles tend to live a lot longer (mail messages might live for
months or years in a users mailbox, but that's not /var/spool/mqueue,
and has a different pattern of access), and they tend to be a lot
larger.
However, there are still on the same order of number of
articles/messages input per day versus deleted per day (assuming
you've got a handle on your spool and it's not growing out of control
on you), it just typically takes news servers a few days to delete
something once it comes in.
Thus, the name cache misses might tend to be lower on news
servers, but I wouldn't be too willing to bet on it -- an article
that got created seven days ago and not touched since probably won't
be in the name cache any more than a file that is just now being
created.
Of course, once you get into CNFS or timehash sorts of news spool
storage mechanisms, you've traded the name cache problem and
directory update problems in for an entirely different set of
problems, and the filesystem may or may not be particularly good at
optimizing them, as softupdates is with lots more smaller individual
files.
--
These are my opinions -- not to be taken as official Skynet policy
____________________________________________________________________
|o| Brad Knowles, <[EMAIL PROTECTED]> Belgacom Skynet NV/SA |o|
|o| Systems Architect, News & FTP Admin Rue Col. Bourg, 124 |o|
|o| Phone/Fax: +32-2-706.11.11/12.49 B-1140 Brussels |o|
|o| http://www.skynet.be Belgium |o|
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