Apache HTTP Server Version 1.3

Overview of New Features in Apache 1.3

New features with this release, as extensions of the Apache functionality. Because the core code has changed so significantly, there are certain liberties that earlier versions of Apache (and the NCSA daemon) took that recent Apache versions are pickier about - please check the compatibility notes if you have any problems.

If you're upgrading from Apache 1.2, you may wish to read the upgrade notes.

Core Enhancements:

Dynamic Shared Object (DSO) support: Apache modules may now be loaded at runtime; this means that modules can be loaded into the server process space only when necessary, thus overall memory usage by Apache will be significantly reduced. DSO currently is supported on FreeBSD, OpenBSD, NetBSD, Linux, Solaris, SunOS, OSF1, IRIX, HP/UX, UnixWare, AIX, ReliantUnix and generic SVR4 platforms.
Support for Windows NT/95: Apache now experimentally supports the Windows NT and Windows 95 operating systems.
Re-organized Sources: The source files for Apache have been re-organized. The main difference for Apache users is that the "Module" lines in Configuration have been replaced with "AddModule" with a slightly different syntax. For module authors there are some changes designed to make it easier for users to add their module.
Reliable Piped Logs: On almost all Unix architectures Apache now implements "reliable" piped logs in mod_log_config. Where reliable means that if the logging child dies for whatever reason, Apache will recover and respawn it without having to restart the entire server. Furthermore if the logging child becomes "stuck" and isn't reading its pipe frequently enough Apache will also restart it. This opens up more opportunities for log rotation, hit filtering, real-time splitting of multiple vhosts into separate logs, and asynchronous DNS resolving on the fly.

Performance Improvements

IP-based virtual hosts are looked up via hash table.
<Directory> parsing speedups.
The critical path for static requests has fewer system calls. This generally helps all requests. (45 syscalls for a static request in 1.2 versus 22 in 1.3 in a well tuned configuration).
ProxyReceiveBufferSize directive gives mod_proxy's outgoing connections larger network buffers, for increased throughput.
The low level I/O routines use writev (where available) to issue multiple writes with a single system call. They also avoid copying memory into buffers as much as possible. The result is less CPU time spent on transferring large files.
Static requests are served using mmap, which means bytes are only copied from the disk buffer to the network buffer directly by the kernel. The program never copies bytes around, which reduces CPU time. (Only where available/tested.)
When presented with a load spike, the server quickly adapts by spawning children at faster rates.
The code which dispatches modules was optimized to avoid repeatedly skipping over modules that don't implement certain phases of the API. (This skipping showed up as 5% of the cpu time on profiles of a server with the default module mix.)
Revamp of the Unix scoreboard management code so that less time is spent counting children in various states. Previously a scan was performed for each hit, now it is performed only once per second. This should be noticeable on servers running with hundreds of children and high loads.
New serialization choices improve performance on Linux, and IRIX.
mod_log_config can be compile-time configured to buffer writes.
Replaced strncpy() with ap_cpystrn(), a routine which doesn't have to zero-fill the entire result. This has dramatic effects on mod_include speed.
Additions to the internal "table" API (used for keeping lists of key/value string pairs) provide for up to 20% performance improvement in many situations.

See the new performance documentation for more information.

Configuration Enhancements

Apache Autoconf-style Interface (APACI): Until Apache 1.3 there was no real out-of-the-box batch-capable build and installation procedure for the complete Apache package. This is now provided by a top-level configure script and a corresponding top-level Makefile.tmpl file. The goal is to provide a GNU Autoconf-style frontend which is capable to both drive the old src/Configure stuff in batch and additionally installs the package with a GNU-conforming directory layout. Any options from the old configuration scheme are available plus a lot of new options for flexibly customizing Apache.
APache eXtenSion (APXS) support tool: Now that Apache provides full support for loading modules under runtime from dynamic shared object (DSO) files, a new support tool apxs was created which provides off-source building, installing and activating of those DSO-based modules. It completely hides the platform-dependent DSO-build commands from the user and provides an easy way to build modules outside the Apache source tree. To achieve this APACI installs the Apache C header files together with the apxs tool.
Default Apache directory path changed to /usr/local/apache/: The default directory for the apache ServerRoot changed from the NCSA-compatible /usr/local/etc/httpd/ to /usr/local/apache/. This change covers only the default setting (and the documentation); it is of course possible to override it using the -d ServerRoot and -f httpd.conf switches when starting apache.
Improved HTTP/1.1-style Virtual Hosts: The new NameVirtualHost directive is used to list IP address:port pairs on which HTTP/1.1-style virtual hosting occurs. This is vhosting based on the Host: header from the client. Previously this address was implicitly the same as the "main address" of the machine, and this caused no end of problems for users, and was not powerful enough. Please see the Apache Virtual Host documentation for further details on configuration.
Include directive: The Include directive includes other config files immediately at that point in parsing.
-S command line option for debugging vhost setup: If Apache is invoked with the -S command line option it will dump out information regarding how it parsed the VirtualHost sections. This is useful for folks trying to debug their virtual host configuration.

Module Enhancements

NEW - Spelling correction module