I seem to be having a problem occuring about once every two days and I'm unsure why.  I get notification through internal systems telling me that it can't return HTTP requests as the system has reached MaxClients and isn't returning any result to the client.  After investigation, this doesn't appear to be caused by apache, but rather PHP.
 STRACEing any of the processes returns the following:
  select(11, NULL, [10], [10], NULL
and simply sits there, producing no additional output.  A full 'apachectl stop' is required to kill such processes and they all terminate immediately.
 A backtrace of any of these processes is as follows.  I am unsure which of the many scripts (if one in particular) is causing this.  The identical site is being run on a 4.2.3 server without difficulty.
gdb) backtrace
-=-=--=-=-=-=-
#0  0x402fbfbe in __select () at __select:-1
#1  0x00000020 in ?? ()
#2  0x080b9001 in _php_stream_free ()
#3  0x0816a5ef in php_stream_url_wrap_http ()
#4  0x080bbc2a in _php_stream_open_wrapper_ex ()
#5  0x0813c2c9 in php_if_fopen ()
#6  0x080df23c in execute ()
#7  0x080e0439 in execute ()
#8  0x080e0439 in execute ()
#9  0x080d2be8 in zend_execute_scripts ()
#10 0x080b2675 in php_execute_script ()
#11 0x080e25a9 in apache_php_module_main ()
#12 0x080aaa1a in ssl_expr_yyinput ()
#13 0x080aaa90 in ssl_expr_yyinput ()
#14 0x081a6be6 in ap_invoke_handler ()
#15 0x081bc975 in ap_some_auth_required ()
#16 0x081bc9d2 in ap_process_request ()
#17 0x081b33b5 in ap_child_terminate ()
#18 0x081b3664 in ap_child_terminate ()
#19 0x081b39d2 in ap_child_terminate ()
#20 0x081b3fd4 in ap_child_terminate ()
#21 0x081b4649 in main ()
#22 0x40239f14 in __libc_start_main (main=0x81b42ae <main>, argc=1, ubp_av=0xbffffda4, init=0x806f1dc <_init>, 
    fini=0x40015640 <_rtld_local>, rtld_fini=0, stack_end=0xbfff0790) at ../sysdeps/generic/libc-start.c:144
-=-=--=-=-=-=-

  Any thoughts?  It appears to be a bug in PHP somewhere that is causing different activity than 4.2.3.

-M