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The Apache HTTP Server Reference Manual
by Apache Software Foundation
Paperback (6"x9"), 862 pages
ISBN 9781906966034
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8.4  File-Handle Caching

Related Modules

Related Directives



The act of opening a file can itself be a source of delay, particularly on network filesystems. By maintaining a cache of open file descriptors for commonly served files, Apache can avoid this delay. Currently Apache provides two different implementations of File-Handle Caching.

8.4.1  CacheFile

The most basic form of caching present in Apache is the file-handle caching provided by mod_file_cache. Rather than caching file-contents, this cache maintains a table of open file descriptors. Files to be cached in this manner are specified in the configuration file using the CacheFile directive.

The CacheFile directive instructs Apache to open the file when Apache is started and to re-use this file-handle for all subsequent access to this file.

CacheFile /usr/local/apache2/htdocs/index.html

If you intend to cache a large number of files in this manner, you must ensure that your operating system’s limit for the number of open files is set appropriately.

Although using CacheFile does not cause the file-contents to be cached per-se, it does mean that if the file changes while Apache is running these changes will not be picked up. The file will be consistently served as it was when Apache was started.

If the file is removed while Apache is running, Apache will continue to maintain an open file descriptor and serve the file as it was when Apache was started. This usually also means that although the file will have been deleted, and not show up on the filesystem, extra free space will not be recovered until Apache is stopped and the file descriptor closed.

8.4.2  CacheEnable fd

mod_mem_cache also provides its own file-handle caching scheme, which can be enabled via the CacheEnable directive.

CacheEnable fd /

As with all of mod_cache this type of file-handle caching is intelligent, and handles will not be maintained beyond the expiry time of the cached content.

ISBN 9781906966034The Apache HTTP Server Reference ManualSee the print edition