CGI? If I'm having a PHP extension forked along with an apache child process, that extension has initially not had a database connection, but it's established when processing requests,,, that connection can get forked along with a child process? (In other words and repeating myself a bit: apache forks it's child processes after they have already been processing requests?) Note that I'm considering prefork MPM and PHP scripts.
Yes, if you are running PHP as a CGI -- that is, *not* via mod_php -- with the prefork MPM, then the Apache HTTP Server child that is handling the request will fork itself in order to execute the PHP script in a "grandchild" process. However, this has nothing to do with database connections, and, since the PHP interpreter is not persistent -- a new PHP interpreter is started up for each CGI request and exits afterward -- there are no persistent database connections either; each PHP CGI will need to open its own database connection, if it needs one. The order of events is: An Apache HTTP Server child process receives a request for a PHP CGI; the child process forks itself, creating a "grandchild"; the grandchild Apache process immediately invokes the PHP interpreter to replace itself (Apache is no longer running in the grandchild at this point); the PHP interpreter in the grandchild process interprets the PHP script, sending its output to the parent process (the Apache child that is handling the request); the grandchild process terminates itself (exits) as soon as the PHP script has finished running.
But, if you are running PHP inside of Apache HTTP Server by using mod_php and the prefork MPM, the Apache HTTP Server child process that is handling the request will not fork itself. Instead, the PHP script will get run directly inside the Apache process that is handling the request. In this scenario, you can have persistent (cross-request) database connections. The only way the Apache child process will get forked is if a request is made for a non-mod_php CGI (that is, a request that uses mod_cgid) or if a PHP script itself does something that forks the process (such as calling one of the exec() family of functions, system(), or something similar) -- in this case, the the entire Apache HTTP server child process will be (temporarily) duplicated, including the PHP interpreter and any already-established database connections.
These are mostly academic points in response to the question "are there ever circumstances in which an Apache HTTP Server child process will fork itself." If you are using mod_php, don't worry about this. If you are using mod_cgid, don't worry about it either except to keep in mind that forking is a relatively expensive operation, which is one reason why running conventional, external CGIs is slower than using an embedded interpreter or a persistent interpreter in an external daemon (e.g., FastCGI).
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