usef_ksa's questions

My site is working on one web server (Apache+PHP, linux OS) and one DB server (MySQL) and it is facing a lot of traffic. I am planning to add additional web server beside the current one. I did not have experience with multiple web server setup so I need suggestions, advices or ideas about the best setup for two web servers.

Here some nice statistics about current web server:

The current Apache configuration is the following:

<IfModule prefork.c>
StartServers       8
MinSpareServers    5
MaxSpareServers   20
ServerLimit      1556
MaxClients       1556
MaxRequestsPerChild  2000
</IfModule>

Today my DB server reached the maximum number of connections and my web applications (in another server) show "too many connections" error message. After that I restarted MySQL server but a new problem shown. The applications start showing another error " Can't connect to MySQL server  'DB server IP' on (4)". I can connect to MySQL locally and run quires without any problem. I can telnet from web-server to port # 3306 in the DB server. I cleared the MySQL error log file and I did the test again but I did not find any problem. I restarted both servers to make sure all connections are killed but still the same problem exists after restarting the servers. Network is fine, no network problem between both servers, no packets drop, no latency, no error messages.After three hours the DB server back to work normally!

what is the expected reasons for this problem? Why the server back to work after three hours? is there any time-out parameter related to this?

 Edit: My application is PHP and web-server is apache2.

what is the meaning of Apache busy workers and idle workers? how the statistic of them help me to figure out performance problem with my server?

I have detected server that I can access using supermicro IPMI. I need to reinstall the OS (linux centos 5) because the current OS cannot boot (kernel panic problems). how can I do that?

How to switch from prefork mpm to worker mpm on ubuntu server?
how to roll back if there is any problem?

    root@myserver:~# apache2ctl -l
Compiled in modules:
core.c
mod_log_config.c
mod_logio.c
prefork.c
http_core.c
mod_so.c
root@myserver:~# aptitude search apache2-mpm-
p   apache2-mpm-event                                                      - Event driven model for Apache HTTPD
p   apache2-mpm-itk                                                        - multiuser MPM for Apache 2.2
p   apache2-mpm-perchild                                                   - Transitional package - please remove
i A apache2-mpm-prefork                                                    - Traditional model for Apache HTTPD
p   apache2-mpm-worker                                                     - High speed threaded model for Apache HTTPD
root@myserver:~#

Thanks in advance.

Is there any good website to keep Syslog events? I need a website to manage Syslog events and group them based on their priority.

I have a new server for only images. what is the recommended web server to serve only static content (I have only images) ?
My hardware is:
CPU: intel xeon X3460
RAM: 16G

OS is CentOS5

I have a forum with a lot of visitors, Some days the load increase to reach 40 without increase of the number vistors. As you can see from the below output, the waiting time is high (57%). how do I find the reason for that?
The server software is Apache, MySQL and PHP.

root@server:~# top
top - 13:22:08 up 283 days, 22:06,  1 user,  load average: 13.84, 24.75, 22.79
Tasks: 333 total,   1 running, 331 sleeping,   0 stopped,   1 zombie
Cpu(s): 20.6%us,  7.9%sy,  0.0%ni, 13.4%id, 57.1%wa,  0.1%hi,  0.9%si,  0.0%st
Mem:   4053180k total,  3868680k used,   184500k free,   136380k buffers
Swap:  9936160k total,    12144k used,  9924016k free,  2166552k cached

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
23930 mysql     20   0  549m 122m 6580 S   90  3.1   4449:04 mysqld
17422 www-data  20   0  223m  20m  10m S    2  0.5   0:00.21 apache2
17555 www-data  20   0  222m  19m 9968 S    2  0.5   0:00.13 apache2
17264 www-data  20   0  225m  19m 8972 S    1  0.5   0:00.17 apache2
17251 www-data  20   0  220m  12m 4912 S    1  0.3   0:00.12 apache2

.

root@server:~# top
top - 13:39:59 up 283 days, 22:24,  1 user,  load average: 6.66, 10.39, 13.95
Tasks: 318 total,   1 running, 317 sleeping,   0 stopped,   0 zombie
Cpu(s): 13.6%us,  4.2%sy,  0.0%ni, 40.5%id, 40.6%wa,  0.2%hi,  0.8%si,  0.0%st
Mem:   4053180k total,  4010992k used,    42188k free,   119544k buffers
Swap:  9936160k total,    12160k used,  9924000k free,  2290716k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
23930 mysql     20   0  549m 122m 6580 S   44  3.1   4457:30 mysqld
19946 www-data  20   0  223m  21m  10m S    5  0.6   0:00.77 apache2
17316 www-data  20   0  226m  23m  11m S    1  0.6   0:01.76 apache2
17333 www-data  20   0  222m  21m  11m S    1  0.5   0:01.55 apache2
18212 www-data  20   0  225m  22m  11m S    1  0.6   0:01.58 apache2
19528 www-data  20   0  220m  13m 5480 S    1  0.3   0:00.63 apache2
19600 www-data  20   0  224m  20m  11m S    1  0.5   0:00.73 apache2
19942 www-data  20   0  225m  21m  10m S    1  0.5   0:00.82 apache2
20232 www-data  20   0  222m  16m 8760 S    1  0.4   0:00.65 apache2
20243 www-data  20   0  223m  21m  11m S    1  0.5   0:00.57 apache2
20299 www-data  20   0  225m  20m   9m S    1  0.5   0:00.67 apache2
20441 www-data  20   0  225m  21m  10m S    1  0.5   0:00.57 apache2
21201 www-data  20   0  220m  12m 5148 S    1  0.3   0:00.19 apache2
21362 www-data  20   0  220m  12m 5032 S    1  0.3   0:00.17 apache2
21364 www-data  20   0  220m  12m 4916 S    1  0.3   0:00.14 apache2
21366 www-data  20   0  220m  12m 5124 S    1  0.3   0:00.22 apache2
21373 www-data  20   0  222m  14m 7060 S    1  0.4   0:00.26 apache2

I have Apache +Mysql+ PHP installed on 4G memory server which serve around 20000 visits per day. The following graph shows the memory utilization for one day. As you can see from the graph: the free memory is low (e.g 155 M) and the cached memory is high (e.g 2G). This server did not use the swap memory ever.

• do I need to increase the memory?
• Is it safe to have low free memory but high cached memory?
• How do I find which application using a lot of cache memory?

Thanks a lot for help.