Re: [squid-users] 4 second Cache Miss Service Times

--On June 16, 2006 10:43:04 AM +0300 Ben Hathaway
<ben.hathaway@spidersat.net> wrote:

> Dear All,
>
> I have recently set up a Squid cache using WCCP and a cisco router.
> I am getting very impressive performance for my cache hits, but my cache
> misses sometimes take as long as 4 seconds! We are at the end of a high
> bandwidth, high latency satellite link with a normal latency (for example:
> to google.com) of around 600ms round-trip. So why the 4 second delay?
> Sometimes it comes down to 1.3sec but even that is a lot slower than I
> would expect when my cache hits are being pumped out in 0.017s
>
> Any ideas?

Everything sounds fine to me...it can easily take 4*RTT to start getting
data across a link. 3*RTT to establish the TCP/IP connection, then about
one more RTT to send your HTTP request upstream.

What you might want to do is try tuning your squid servers TCP window sizes
to be quite a bit larger. I don't know what OS you're using but a little
bit of google searching will find you an answer. You'll have two or more
sysctl's or /etc/sysctl.conf entries or similar in order to adjust the
window sizes.

At the latency you're seeing it's possible TCP has more data in-flight than
it will normally allow, so it's stopping and waiting on the in-flight data,
possibly even re-transmitting because it thinks data has been lost.
Received on Fri Jun 16 2006 - 07:29:53 MDT