HP Apache-based Web Server
v.2.0.0

Tuning notes: HP Apache-based Web Server v.2.0.0 technology preview on HP-UX 11.0 and 11i (PA-RISC)

These tuning notes are based on
http://httpd.apache.org/docs-2.0/misc/perf-tuning.html#runtime,
Other documents and in-house testing.

These notes provide tips on configuring your HP Apache-based Web Server through the smart use of directives and modules, as well as tuning your HP-UX environment.

Using directives

1. Hostname lookups

   http://httpd.apache.org/docs-2.0/mod/core.html#hostnamelookups If HostNameLookups is not turned off, each client request will result in at least one lookup request to the name server.

   Example:
   HostNameLookups off		##Turning off DNS lookups

2. Logging

   - Avoid use debug, info and notice level.
   - Disable referer_log and agent_log, if you don't need to keep track of client information.

3. FollowSymLinks and SymLinksIfOwnerMatch

   Wherever in your URL-space you do NOT have an "Options FollowSymLinks", or you do have an "Options SymLinksIfOwnerMatch," Apache will issue extra system calls to check up on symlinks. One extra call per filename component will be made. For example, if you had:

   DocumentRoot /www/htdocs
   <Directory />
   Options SymLinksIfOwnerMatch
   </Directory>

   If a request is made for the URI /index.html, Apache will perform lstat(2) on /www, /www/htdocs, and /www/htdocs/index.html. The results of these lstats are never cached, so they will occur on every single request. If you really desire the symlinks security checking try the following instead:

   DocumentRoot /www/htdocs
   <Directory />
   Options FollowSymLinks
   </Directory>
   <Directory /www/htdocs>
   Options -FollowSymLinks +SymLinksIfOwnerMatch
   </Directory>

   This at least avoids the extra checks for the DocumentRoot path. Note that you'll need to add similar sections if you have any Alias or RewriteRule paths outside of your document root. For highest performance, and no symlink protection, set FollowSymLinks everywhere, and never set SymLinksIfOwnerMatch.

4. AllowOverride

   Wherever in your URL-space you allow overrides (typically .htaccess files) Apache will attempt to open .htaccess for each filename component. For highest performance use AllowOverride None everywhere in your filesystem.

5. Negotiation

   Use a complete list of options for DirectoryIndex, listing the most common choice first.

   Example: DirectoryIndex index.cgi index.pl index.shtml index.html

6. Tune NumServers, StartThreads, MinSpareThreads, MaxSpareThreads, MaxThreadsPerChild, MaxRequestsPerChild

   Apache tries to maintain a pool of spare or idle server threads, which stand ready to serve incoming requests. In this way, clients do not need to wait for a new threads or processes to be created before their requests can be served. Apache assesses the total number of idle threads in all processes, and forks or kills processes to keep this number within the boundaries specified by MinSpareThreads and MaxSpareThreads. Since this process is very self-regulating, it is rarely necessary to modify these directives from their default values. The maximum number of clients that may be served simultaneously is determined by multiplying the maximum number of server processes that will be created (MaxClients) by the number of threads created in each process (ThreadsPerChild).

Using modules

1. Disable unused modules

   Enable only the modules you need. Pre-processing and post-processing modules like mod_speling, mod_include and mod_log_config create a lot of overhead. Use http://httpd.apache.org/docs-2.0/mod/index.html to determine which modules are used with your configuration, and which you can remove.

2. mod_vhost_alias

   This module uses less memory than VirtualHost directive, when it is used for a huge number of virtual hosts with similar configurations.

3. mod_perl

   In CGI scripts, using mod_perl is 10 times faster than regular CGI.

Configuring HP-UX environment

1. Tuning the OS

   Tune kernel parameters maxproc, shmem, maxfd, etc.

2. Monitor the memory

   Make sure the web server has enough memory.

3. Renice

   Increase the priority of Apache process.

4. TCP/IP parameters tuning

   You might want to tune the system listen queue when you receive errors relating to insufficient buffer space (ENOBUFS) error from client socket.

   On HP-UX 11.x the system listen queue parameter is called tcp_conn_request_max. The utility for listing/modifying network settings is called "ndd".

   The following are equivalent commands to use on HP-UX 11.x:

   - To check the current setting of the system listen queue: ndd -get /dev/tcp tcp_conn_request_max

   - To adjust the system listen queue size to 256, for example: ndd -set /dev/tcp tcp_conn_request_max 256