为什么Apache无法在Windows上以高并发率提供静态内容？

Question

When testing Apache 2.4.16 on windows 7,8,2012 there is a severe limitation when serving static content. Apache can't serve more than 700 concurrent requests for static content with Keep Alive OFF.

When you attempt to do that one of two things will happen:

1. You will be able to server few thousand requests at first and then the remaining requests will take up to 10 seconds to complete. OR
2. You will receive a connection refused error

Test method:

siege -b -c700 -t10s -v http://10.0.0.31/10k.txt    (10KB file)

OR

ab -c 700 -n 40000 http://10.0.0.31/10k.txt 

However, when testing with Apache bench on the localhost (bypassing the network) Apache works fine and can serve 1000 concurrent requests for 10K static file.

Apache has ThreadsPerChild 7000 (increasing it to 14000 didn't make any difference)
MaxConnectionsPerChild 0

Stack parameters:
MaxUserPort = 65534
TcpTimedWaitDelay = 30
Server has over 60,000 ephemeral ports available starting with port 5,000 to port 65534

• My load testing server is Linux on a separate server and sends requests over the network to Apache Windows server over 10Gb/s network.

• There are no errors in the Apache log and nothing in the system logs. The tasklist doesn't show anything unusual.

• netstat shows few thousand (5,000) of open TCP connections and then Apache stops responding. However when testing with lower concurrency of 300 then the OS can open 60,000 of TCP connections and Apache works fine.

Potential Conclusions: At first I thought this is OS stack tuning problem but serving php file with the same concurrency works fine.

ab -c 700 -n 10000 http://10.0.0.31/phpinfo.php

Then I tried Nginx for windows on the same machine and Nginx served this without a problem.

ab -c 700 -n 10000 http://10.0.0.31/10k.txt

Nginx was able to serve much higher concurrency up to 2000 requests per second (static content) and the OS opened about 40,000 TCP connections.

So this looks to me like a bug or a limitation in the way Apache communicates with the TCP/IP stack on windows.

When trying to duplicate this problem make sure Keep Alive is OFF and test it over the network (not on localhost).

Any answers or comments on this subject will be greatly appreciated.

Answer 1

Thanks to covener's suggestion here is the answer.

1. Keep Alive was intentionally disabled to simulate a large number of users connecting from different IP addresses and spawning new TCP connections.

2. Setting AcceptFilter http to "none" together with turning off MultiViews improved the performance on static content and allowed Apache on windows to serve with concurrency of 2000 and beyond untill all ephemeral ports get exhausted.