The
To use the --with-mpm=event
to the
This MPM tries to fix the 'keep alive problem' in HTTP. After a client
completes the first request, the client can keep the connection
open, and send further requests using the same socket. This can
save signifigant overhead in creating TCP connections. However,
Apache HTTP Server traditionally keeps an entire child process/thread waiting
for data from the client, which brings its own disadvantages. To
solve this problem, this MPM uses a dedicated thread to handle both
the Listening sockets, all sockets that are in a Keep Alive state,
and sockets where the handler and protocol filters have done their work
and the only remaining thing to do is send the data to the client. The
status page of
The improved connection handling does not yet work for certain
connection filters, in particular SSL. For SSL connections, this MPM will
fall back to the behaviour of the
The MPM assumes that the underlying apr_pollset
implementation is reasonably threadsafe. This enables the MPM to
avoid excessive high level locking, or having to wake up the listener
thread in order to send it a keep-alive socket. This is currently
only compatible with KQueue and EPoll.
This MPM depends on --enable-nonportable-atomics=yes
to the
This MPM does not perform well on older platforms which lack good threading, but the requirement for EPoll or KQueue makes this moot.
libkse
(see man libmap.conf
).glibc
has been compiled
with support for EPoll.The event MPM handles some connections in an asynchronous way, where request worker threads are only allocated for short periods of time as needed, and other (mostly SSL) connections with one request worker thread reserved per connection. This can lead to situations where all workers are tied up and no worker thread is available to handle new work on established async connetions.
To mitigate this problem, the event MPM does two things: Firstly, it limits the number of connections accepted per process, depending on the number of idle request workers. Secondly, if all workers are busy, it will close connections in keep-alive state even if the keep-alive timeout has not expired. This allows the respective clients to reconnect to a different process which may still have worker threads available.
This directive can be used to fine-tune the per-process connection limit. A process will only accept new connections if the current number of connections is lower than:
This means the absolute maximum numbers of concurrent connections is:
(