Apache performance optimization (4)

The following is the default configuration section of prefork:

StartServers 5 //

MinSpareServers 5 //The minimum number of idle processes is set.

MaxSpareServers 10 //Set the maximum number of idle processes. If the number of idle processes is greater than this value, Apache will automatically kill some redundant processes. Do not set this value too large, but if the value is smaller than MinSpareServers, Apache will automatically adjust it to MinSpareServers+1. If the site load is heavy, consider increasing both MinSpareServers and MaxSpareServers.

MaxClients 150 // MaxClients is the most important of these instructions. It sets the requests that Apache can handle at the same time and is the parameter that has the greatest impact on Apache performance. The default value of 150 is far from enough. If the total number of requests has reached this value (can be confirmed by ps -ef|grep http|wc -l), then subsequent requests will be queued until a processed request is completed. . This is the main reason why there are a lot of system resources left but HTTP access is very slow. System administrators can dynamically adjust this value based on hardware configuration and load conditions. Although theoretically the larger this value, the more requests that can be processed, Apache's default limit cannot be greater than 256 (derived from #define DEFAULT_SERVER_LIMIT 256 in 2.0). If this value is set to greater than 256, Apache will not start. In fact, 256 is not enough for sites with slightly heavier loads. In Apache 1.3, this is a hard limit. If you want to increase this value, you must search for 256 in src/include/httpd.h under the source code tree that was manually modified before "configure", and you will find the line "#define HARD_SERVER_LIMIT 256". Change 256 to the value you want to increase (such as 4000), and then recompile Apache. The ServerLimit directive was newly added to Apache 2.0, so that MaxClients can be increased without recompiling Apache. When using ServerLimit, just add a separate line here. If the value of ServerLimit exceeds 20000 as defined here, you must modify server/mpm/prefork/prefork.c #define MAX_SERVER_LIMIT 20000. Change 20000 to a larger value.

MaxRequestsPerChild 0 //Set the number of requests that each child process can handle. Each child process will be automatically destroyed after processing "MaxRequestsPerChild" requests. 0 means infinite, that is, the child process is never destroyed. Although the default setting of 0 allows each child process to handle more requests, setting it to a non-zero value also has two important benefits: it can prevent accidental memory leaks; it will automatically reduce the number of child processes when the server load decreases. number.

The working principle of worker is that the main control process generates "StartServers" sub-processes. Each sub-process contains a fixed number of ThreadsPerChild threads, and each thread processes requests independently. Likewise, in order not to spawn threads when requests come in.

The number of threads each process can have is fixed. The server will adjust to increase or decrease the number of processes based on load conditions. A single controlling process is responsible for the establishment of child processes. Each child process can create a fixed number of threads specified by ThreadsPerChild. Then, a separate thread listens for and handles incoming connections.

Apache always tries to maintain a spare or idle service thread pool. In this way, the client does not need to wait for the thread or process to be established before it can be processed. The number of processes initially created is determined by the StartServers directive. Afterwards, Apache detects the total number of idle threads in all processes, and creates or ends processes to keep the total number within the range specified by MinSpareThreads and MaxSpareThreads. Since this process is self-tuning, there is little need to modify the default values ​​of these instructions. The maximum number of clients that can be processed simultaneously depends on the MaxClients directive, and the maximum number of processes established depends on the ServerLimit directive. ServerLimit multiplied by ThreadsPerChild must be greater than or equal to MaxClients.

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