Web Performance Tuning

Compile-Time Configuration Issues

mod_status and Rule STATUS=yes

If you include mod_status and you also set Rule STATUS=yes when building Apache, then on every request Apache will perform two calls to gettimeofday(2) (or times(2), depending on your operating system), and (pre-1.3) several extra calls to time(2). This is all done so that the status report contains timing indications. For highest performance, set Rule STATUS=no:

Accept Serialization—Multiple Sockets

This section discusses a shortcoming in the Unix socket API. Suppose your web server uses multiple Listen statements to listen on either multiple ports or multiple addresses. In order to test each socket to see if a connection is ready, Apache uses select(2). select(2) indicates that a socket has either no connections or at least one connection waiting on it. Apache’s model includes multiple children, and all the idle ones test for new connections at the same time. A naive implementation looks something like this (these examples do not match the code, they’re contrived for pedagogical purposes):

for (;;) { for (;;) { fd_set accept_fds; FD_ZERO (&accept_fds); for (i = first_socket; i <= last_socket; ++i) { FD_SET (i, &accept_fds); } rc = select (last_socket+1, &accept_fds, NULL, NULL, NULL); if (rc < 1) continue; new_connection = -1; for (i = first_socket; i <= last_socket; ++i) { if (FD_ISSET (i, &accept_fds)) { new_connection = accept (i, NULL, NULL); if (new_connection != -1) break; } } if (new_connection != -1) break; } ...