How it Works

How it Works -

Each process has a fixed - number of threads. The server adjusts to handle load by - increasing or decreasing the number of processes.

- -

A single control process is responsible for launching child - processes. Each child process creates a fixed number of threads as - specified in the ThreadsPerChild directive. The - individual threads then listen for connections and serve them when - they arrive.

A single control process (the parent) is responsible for launching + child processes. Each child process creates a fixed number of server + threads as specified in the ThreadsPerChild directive, as well + as a listener thread which listens for connections and passes them + to a server thread for processing when they arrive.

Apache always tries to maintain a pool of spare or idle server threads, which stand ready to serve incoming @@ -54,25 +50,57 @@ these directives from their default values. The maximum number of clients that may be served simultaneously (i.e., the maximum total number of threads in all processes) is determined by the - MaxClients directive, - while the maximum number of processes that can be launched is set - by the ServerLimit - directive. ServerLimit - multiplied by ThreadsPerChild must be greater - than or equal to MaxClients

+ MaxClients directive. + The maximum number of active child processes is determined by + the MaxClients + directive divided by the + ThreadsPerChild directive.

+ +

Two directives set hard limits on the number of active child + processes and the number of server threads in a child process, + and can only be changed by fully stopping the server and then + starting it again. ServerLimit + is a hard limit on the number of active child + processes, and must be greater than or equal to the + MaxClients + directive divided by the + ThreadsPerChild directive. + ThreadLimit is a hard + limit of the number of server threads, and must be greater than + or equal to the ThreadsPerChild directive. If + non-default values are specified for these directives, they + should appear before other worker directives.

+ +

In addition to a the set of active child processes, there may + be additional child processes which are terminating but where at + least one server thread is still handling an existing client + connection. Up to MaxClient terminating processes + may be present, though the actual number can be expected to be + much smaller. This behavior can be avoided by disabling the + termination of individual child processes, which is achieved by + the following:

+ +

set the value of + MaxRequestsPerChild to zero
set the value of + MaxSpareThreads to the same value as + MaxClients

A typical configuration of the process-thread controls in the worker MPM could look as follows:

+ ServerLimit 16
StartServers 2
MaxClients 150
MinSpareThreads 25
MaxSpareThreads 75
- ThreadsPerChild 25
- ServerLimit 16 + ThreadsPerChild 25

While the parent process is usually started as root 1.15.2.6 +45 -17 httpd-2.0/docs/manual/mod/worker.html.en Index: worker.html.en =================================================================== RCS file: /home/cvs/httpd-2.0/docs/manual/mod/worker.html.en,v retrieving revision 1.15.2.5 retrieving revision 1.15.2.6 diff -u -r1.15.2.5 -r1.15.2.6 --- worker.html.en 29 May 2003 19:29:53 -0000 1.15.2.5 +++ worker.html.en 12 Jan 2004 16:30:19 -0000 1.15.2.6 @@ -79,15 +79,11 @@

How it Works

Each process has a fixed - number of threads. The server adjusts to handle load by - increasing or decreasing the number of processes.

- -

A single control process is responsible for launching child - processes. Each child process creates a fixed number of threads as - specified in the ThreadsPerChild directive. The - individual threads then listen for connections and serve them when - they arrive.

A single control process (the parent) is responsible for launching + child processes. Each child process creates a fixed number of server + threads as specified in the ThreadsPerChild directive, as well + as a listener thread which listens for connections and passes them + to a server thread for processing when they arrive.

Apache always tries to maintain a pool of spare or idle server threads, which stand ready to serve incoming @@ -102,23 +98,55 @@ these directives from their default values. The maximum number of clients that may be served simultaneously (i.e., the maximum total number of threads in all processes) is determined by the - MaxClients directive, - while the maximum number of processes that can be launched is set - by the ServerLimit - directive. ServerLimit - multiplied by ThreadsPerChild must be greater - than or equal to MaxClients

+ MaxClients directive. + The maximum number of active child processes is determined by + the MaxClients + directive divided by the


  +    ThreadsPerChild

directive.

+ +

Two directives set hard limits on the number of active child + processes and the number of server threads in a child process, + and can only be changed by fully stopping the server and then + starting it again. ServerLimit + is a hard limit on the number of active child + processes, and must be greater than or equal to the + MaxClients + directive divided by the + ThreadsPerChild directive. + ThreadLimit is a hard + limit of the number of server threads, and must be greater than + or equal to the ThreadsPerChild directive. If + non-default values are specified for these directives, they + should appear before other worker directives.

+ +

In addition to a the set of active child processes, there may + be additional child processes which are terminating but where at + least one server thread is still handling an existing client + connection. Up to MaxClient terminating processes + may be present, though the actual number can be expected to be + much smaller. This behavior can be avoided by disabling the + termination of individual child processes, which is achieved by + the following:

+ +

set the value of + MaxRequestsPerChild to zero
set the value of + MaxSpareThreads to the same value as + MaxClients

A typical configuration of the process-thread controls in the worker MPM could look as follows:

+ ServerLimit 16 StartServers 2 MaxClients 150 MinSpareThreads 25 MaxSpareThreads 75 - ThreadsPerChild 25 - ServerLimit 16 + ThreadsPerChild 25

While the parent process is usually started as root