Ask you about apache configuration

For more information about apache configuration-Linux Enterprise Application-Linux server application, see the following. Let's take a look at it first! Let's take a closer look.
Server hardware:
Cpu: dual-core p4 2.0
2 GB memory
Hard Disk 150 GB
Software: redhat contos5 + apache2.2.3 + php5.1.2 + mysql5

Apache + php + mysql are compiled by yourself
Website traffic pv20000/day

Apache uses prefork. c
The main configuration is as follows:

StartServers 10
MinSpareServers 10
MaxSpareServers 15
ServerLimit 2500
MaxClients 2000
MaxRequestsPerChild 10000


Sometimes at the peak of 3-4 pm
The website cannot be opened, but the server is not closed,
View apache Error Log display by me
Apache error prompt on the afternoon of the 5 th:
[Mon Jan 05 15:15:12 2009] [error] [client 123.128.90.202] request failed: error reading the headers,
Apache error prompt on the afternoon of the 6th:
[Tue Jan 06 15:17:02 2009] [error] [client 120.7.128.119] request failed: error reading the headers
[Tue Jan 06 15:17:02 2009] [error] [client 120.7.128.119] request failed: error reading the headers
Apache error prompt on the afternoon of the 7 th:
[Wed Jan 07 16:23:23 2009] [error] [client 60.223.26.17] request failed: error reading the headers,
No. 8
On the 9th, an apache error message is displayed at night:

[Fri Jan 09 20:41:07 2009] [error] [client 123.4.58.86] request failed: error reading the headers
[Fri Jan 09 20:41:42 2009] [error] [client 119.177.27.136] request failed: error reading the headers

Now I have google but I have no results;
I would like to ask if you have experienced experts to help me analyze whether my apache prefork. c configuration is incorrect.
If you have experience, let me know. Thank you!