Apache HTTP Server Version 2.2
Apache HTTP Server Version 2.2
| Description: | A partially asynchronous variant of the standard worker
MPM |
|---|---|
| Status: | MPM |
| Module Identifier: | mpm_event_module |
| Source File: | event.c |
The event Multi-Processing Module (MPM) is
designed to allow more requests to be served simultaneously by
passing off some processing work to supporting threads, freeing up
the main threads to work on new requests. It is based on the
worker MPM, which implements a hybrid
multi-process multi-threaded server. Run-time configuration
directives are identical to those provided by
worker.
To use the event MPM, add
--with-mpm=event to the configure
script's arguments when building the httpd.
AcceptMutex CoreDumpDirectory EnableExceptionHook Group
IHSDrainKeepaliveConnectionsDuringShutdown Listen ListenBacklog LockFile MaxClients MaxMemFree MaxRequestsPerChild MaxSpareThreads MinSpareThreads PidFile ScoreBoardFile SendBufferSize ServerLimit StartServers ThreadLimit ThreadsPerChild ThreadStackSize User
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 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, and all sockets that are in a Keep Alive state.
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 APR's atomic
compare-and-swap operations for thread synchronization. If you are
compiling for an x86 target and you don't need to support 386s, or
you are compiling for a SPARC and you don't need to run on
pre-UltraSPARC chips, add
--enable-nonportable-atomics=yes to the
configure script's arguments. This will cause
APR to implement atomic operations using efficient opcodes not
available in older CPUs.
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.| Description: | Set graceful process termination options |
|---|---|
| Syntax: | IHSDrainKeepaliveConnectionsDuringShutdown [on|off] |
| Default: | IHSDrainKeepaliveConnectionsDuringShutdown OFF |
| Context: | server config |
| Status: | MPM |
| Module: | event |
| Compatibility: | Requires PI74119 (9.0.0.3) |
Prior to PI74119, when a server process is gracefully terminating, idle keepalive connections are not closed until the entire process exits. If the process does not exit quickly, requests may arrive on those idle connections that will not be handled.
After PI74119, the server immediately shuts down the writing side of its connection with
each idle client, notifying them that the keepalive connection is no longer usable. If this
happens simultaneously with a client re-using a keepalive connection, on a request that is
relatively large, the client may not see the servers socket shutdown. IHSDrainKeepaliveConnectionsDuringShutdown instructs the server to read from
the client in an attempt to have the shutdown noticed. This requires tieing up a processing
thread during shutdown for each such connection.
The HTTP protocol specification says that clients must cope with nearly simultaneous closes of keepalive connections.