Author: Victor Churchill Date: To: Hampshire LUG Discussion List Subject: [Hampshire] a strange web server anomaly?
This has me really puzzled.
I have an Apache setup to write a custom_log with the %D field to tell
me the server response time for each request. And I am seeing a very
strange pattern.
It seems that for one particular client IP address, when the page they
are being served includes a particular image, the server frequently
times out delivering the image. The image is fine served to other
clients; the client IP gets fine response on (some) other pages. It's
not particularly big.
A small example of the results - format is filename:line-number:IP
Address,http status, size, etc. The final field is the time in
microseconds):
287 lines with response >= 90s
139 occurrences of K0002.jpg
151 occurrences for 194.73.99.134
So :
- one image file accounts for almost half the server timeouts;
- more than half the timeouts come serving this one address;
- the image times out 40% of the time it is served;
- 2/3 of the time this image is served it is going to this one user;
- this user experiences timeouts on 10% of hir page hits;
- s/he calls up the meter page with this image 15% of hir page hits.
But correspondingly, the user gets OK responses on other pages, the
image is OK going to other userrs, we get timeouts for other users
doing other stuff.
This has me quite bewildered. This user may be operating behind some
corporate firewall router, I don't know. I set up a trial where I
hammered the server overnight pulling this one image repeatedly from a
couple of addresses, and had responses consistently around 0.1 second.
