more on bogged down server

[Rick Stevens]

On Mon, 2006-04-10 at 15:53 -0700, Harold Hallikainen wrote:
> >
> >> You have to reduce your load somehow.  Ideally, you should create an
> anonymous FTP download directory and move all of the downloadable files
> to it.  The download directory also is used as the home directory for
> the anonymous FTP user (user "ftp").  I actually use a completely
> separate filesystem entirely for that.  The filesystem is mounted so
> that only root has write access.
> >> Modify your vsftpd.conf file to permit anonymous downloads only and
> start up vsftpd.  Make sure you also set the "force chroot for
> anonymous users" option.  Then change your links on your web pages to
> use "ftp://"-style links pointed at the anonymous download directory
> paths for the downloadable files.
> >> FTP is the protocol to use for large file downloads.  HTTP just isn't
> efficient for that, as you've now found out (the hard way, I might
> add).
> >
> > as the man said, dont use http for this,
> >
> > if you must then i suggest that you have a separate partition for your
> large files and make fstab read as such (example)
> >
> > /dev/web /                       ext3    defaults,directio        1 1
> >
> > add the directio comment and the file will not go to ram, nor to swap.
> this will speed up things, but you should hand the downloads over to a
> different method (not http).
> >
> 
> THANKS! I'll see what I can do about moving stuff to ftp. Most of the
> large files are on phpwiki. I suppose I could slowly go through the pages
> and change the download files (mostly scanned pdfs) from http:// to ftp://
> . Any problem with having the ftp download directory being the same as the
> http root directory? That way I would not have to move anything, just
> change the protocol prefix on the links.

Well, I would rather not have anonymous FTP sessions chrooting to my
web server pages, but that's up to you.  Just realize that you may be
opening some security holes.  Make sure the anonymous FTP user doesn't
have ANY form of write access to the files (make sure they're owned by
someone other than "ftp" and group "ftp") and make sure the directories
are owned by a secure user and have 755 permissions ("rwxr-xr-x").

> Here's another top. It looks like 98.6% of ram is being used, along with
> 100% of the processor. Not much swap space is being used. It kinda seems
> like Apache just tries to use as much RAM and CPU as is available. I guess
> this would be ok if my DSL could send the data out faster (I'm sure that's
> why these threads live so long). But, it doesn't seem like it should 7% or
> more of the CPU to a byte from the drive to the ethernet. Maybe ftp's just
> more efficient at this?

Yes, FTP is much more adept at this.  You also have to remember that
you have an entire copy of Apache running for each connected user.  If
you were to do a "vmstat 3", you'll probably see a hell of a lot of
context switches going on (the stuff under the "cs" column), and that's
where your CPU is going.  A context switch occurs when the system
switches from executing one program to another.  There are conditions
where the system spends all its time switching and not doing anything
else (we lovingly call this the "scratching the process itch").

As another poster has commented, strip your apache down as much as
possible.  If you aren't using it, kill off mod_perl (it's a huge
resource hog), optimize and precompile your PHP stuff (using zend). But
your best thing is FTP.

Also note that residential DSL is generally optimized to have a big
incoming pipe (for downloads FROM the net TO you) and a much smaller
pipe going the other way.  And the upload pipe is usually time-
multiplexed...you share the upload bandwidth with other users.  So,
rather than sending a lot of data to a client, you can only send a
little bit, then the system switches to another task, sends a tiny bit
there, switches to yet another and so on and so on.  This is obviously
not the best scenario for running an FTP or Wiki site.

FTP will help (since it's a lighter process and the protocol is
optimized for sending lots of data), but a large part of your problem is
likely the DSL connection itself, and I can't help much with that except
tell you to see if your DSL provider can give you a symmetrical DSL
connection (a.k.a. "business DSL")--and that'll probably cost you more.
That's why there are companies that offer co-location, managed servers
or web hosting services.  They have high speed, bidirectional pipes to
the internet and you (usually) don't get bottlenecked at the network
pipe, which is what you're experiencing.

Sorry I can't help more than that.

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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-    I don't suffer from insanity...I enjoy every minute of it!      -
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