Re: Is squid unable to handle the load?

On Wed, 27 May 1998 10:45:36 +0200 (MET DST), Morten Guldager Jensen
wrote:

>On Wed, 27 May 1998, Markus Storm wrote:
>Will it help? I don't think so.
>
>As far as I know, Squid does sequential disk IO.
>
>So when Squid decides to read a file, everything else has to wait. Then
>you are waisting the additional disk IO bandwidt comming from the
>multiple disk drives.
>

If all squid does was read that might be true, but you forget it also
stores it's cache and log files and the OS buffers those writes...
While it is reading that file on one disk, the OS can be catching up on
the writes to the other disks.... It is also good to have all the log
files on one or more disks (maybe with swap and OS but watch the disk
load and RAM), as they are always growing... If you have only one
disk, then under heavy load the machine will not be able to delay any
more writes and will slow down the reads.... Even worse, is if your
swap is on the same drive, and the load is causing you to run out of
buffer space for the writes, which then convinces the OS to swap some
stuff out causing more writes, and a need to read that stuff back in
later..... Just give the OS enough drives to spread the writes to
without slowing down the reads, and squid will be much happier under
heavy loads...

PS: At least on my system (I'm running a little more then just squid,
so cann't say for sure it's just squid), my total writes-per-second is
generally > my reads-per-second. Meaning, you want more then just 2
drives to keep the drives idle enough for reads to take priority over
writes...
Received on Wed May 27 1998 - 05:33:42 MDT