apache 408 status code in 2.2.18 later (Apache Users)

I sent this mail to users@xxxxxxxxxxxxxxxx but at 06 JAN, but i can't find that mail in mailing list

so i send to mail again,

< --original contents-- >

Hello, I send this mail at first time and I had some questions with this enviroment

========================================

- Usage : Image Server(there is no backend system)

- Old one : RHEL5.x, httpd-2.2.17

- New one : RHEL6.x, httpd-2.2.22

- WEB configuration : old and new one same configuration

- OS parameter : limits.conf, security.conf are same thing

========================================

httpd-default.conf

Timeout 15

KeepAlive Off

========================================

httpd-mpm.conf

<IfModule mpm_worker_module>
    ListenBacklog 8192
    ServerLimit  192
    StartServers         20
    MaxClients         12288
    MinSpareThreads     2048
    MaxSpareThreads     8192
    ThreadsPerChild      64
    MaxRequestsPerChild   60000
</IfModule>

==========================================

the problem is that the new one(2.2.22) have the 408 status code in accesslog

183.113.39.228 - - [01/Jan/2014:08:30:11 +0900] "-" 408 - 0
175.241.140.213 - - [01/Jan/2014:08:30:11 +0900] "-" 408 - 0
14.88.50.166 - - [01/Jan/2014:08:30:11 +0900] "-" 408 - 0
175.240.239.52 - - [01/Jan/2014:08:30:11 +0900] "-" 408 - 0
175.253.205.130 - - [01/Jan/2014:08:30:11 +0900] "-" 408 - 0
14.92.97.71 - - [01/Jan/2014:08:30:11 +0900] "-" 408 - 0
175.241.39.59 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0
183.126.29.85 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0
27.237.217.135 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0
115.17.93.229 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0
115.6.162.13 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0
175.226.150.11 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0
175.237.197.228 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0
175.243.106.130 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0
175.253.245.20 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0
118.54.3.227 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0
115.14.245.163 - - [01/Jan/2014:08:30:12 +0900] "-" 408 - 0

and the count of 408 is like this

[root@POSTIMG6 logs]# grep " 408 " access.20131001.log | wc -l

[root@POSTIMG6 logs]# more access.20131001.log | wc -l

10148069

[root@POSTIMG6 logs]# grep " 408 " access.20131002.log | wc -l

[root@POSTIMG6 logs]# grep " 408 " access.20131003.log | wc -l

[root@POSTIMG6 logs]# grep " 408 " access.20131004.log | wc -l

[root@POSTIMG6 logs]# grep " 408 " access.20131005.log | wc -l

[root@POSTIMG6 logs]# grep " 408 " access.20131006.log | wc -l

[root@POSTIMG6 logs]# grep " 408 " access.20131101.log | wc -l

1013

[root@POSTIMG6 logs]# grep " 408 " access.20131115.log | wc -l

2145

[root@POSTIMG6 logs]# grep " 408 " access.20131130.log | wc -l

1668

[root@POSTIMG6 logs]# grep " 408 " access.20131215.log | wc -l

2859

[root@POSTIMG6 logs]# grep " 408 " access.20131216.log | wc -l

3453

[root@POSTIMG6 logs]# grep " 408 " access.20131217.log | wc -l

1747

[root@POSTIMG6 logs]# grep " 408 " access.20131218.log | wc -l

4008

[root@POSTIMG6 logs]# grep " 408 " access.20131219.log | wc -l

7000

[root@POSTIMG6 logs]# grep " 408 " access.20131220.log | wc -l

23146

[root@POSTIMG6 logs]# grep " 408 " access.20131221.log | wc -l

9503

[root@POSTIMG6 logs]# grep " 408 " access.20131222.log | wc -l

101

[root@POSTIMG6 logs]# grep " 408 " access.20131223.log | wc -l

20689

[root@POSTIMG6 logs]# more access.20131223.log | wc -l

14209497

[root@POSTIMG6 logs]# grep " 408 " access.20131224.log | wc -l

10163

[root@POSTIMG6 logs]# grep " 408 " access.20131230.log | wc -l

10946

I search the code of 408 and there are some reasons like this

- the leak of the apache timeout value

- ddos attacks and etc

but I thinks there is not matching above reasons because the old one is not a problem and L4 above the web servers is balancing to the old and new servers in no issues.

I fine some changes between 2.2.17 and 2.2.18 I want to know that the mean of chanelog at 2.2.18 and it will be the reason the 408 status codes.

===========================================================

Changes with Apache 2.2.18

*) core: Only log a 408 if it is no keepalive timeout. PR 39785
[Ruediger Pluem, Mark Montague <markmont umich.edu>]

===========================================================

I understood this substance that if it is no keepalive timeout in apache, all request is return the 408 code. but all of the request are not a return 408 code.

my Questions?

1) which case the code of 408 is mainly cause??

2) what is the meaning of this changes(in 2.2.18) of the sentence?

thanks a lot!!