Give Your Apache a Performance Boost

Caching of web pages is regularly done to speed up access. Let's suppose you
have an Apache web server deployed locally. By deploying mod_cache you can get
the server to regularly update the contents of frequently visited sites. This
way the visitor has access to the latest version of a page as soon as he visits
it and Apache is spared the need to check for it real time. This saves a lot of
bandwidth for enterprises. Apache 2.x also provides the option of integrating
'deflate' module, that allows one to improve the downloading speed by
compressing the downloaded packets.

How the server uses these modules is actually pretty simple. It first checks
if the URL is present in its cache or not. It the URL is present and the version
has not expired, then it serves the page directly from the cache else the page
is loaded from the respective server. In such a scenario (while the page is
being served directly from the server), Apache applies filters to the page to
check if it contains cacheable content or not. In case it's cacheable, then the
web page is cached by mod_cache for future use. It makes use of two other
modules: mod_disk_cache and mod_mem_ cache. Let's see how you can implement this
in real life scenario. Before we start, make sure that mod_cache module is
installed. For this, run the following command, '/usr/sbin/httpd -M.'

This will display all modules that are installed in the Apache module set.
Check if cache module is present or not. If not, then download 'Apache cache
module' rpm package from rpmfind.net and install it on your web server using the
following command:

# rpm —ivh

After you have installed the module, it's time to configure the configuration
file of Apache. This is to tell Apache that it should load the cache module and
use it. Uncomment the following lines in httpd.conf file, in case the line is
marked as a comment; this would allow Apache to load the cache module. The file
can be found at the location: /etc/httpd/ conf/httpd.conf.

LoadModule cache_module modules/mod_cache.so

LoadModule disk_cache_module modules/mod_disk_cache.so

LoadModule file_cache_module modules/mod_mem_cache.so

Apart from the mod_cache module the server needs two other modules:
mod_disk_cache and mod_mem_ cache. Mod_disk_cache is used to for disk based
caching or storing and mod_mem_cache is used for memory based caching. The
second caching option should be used when the content is generated locally. Now
place the following lines into httpd.conf:

CacheRoot /var/www/cache

CacheEnable disk /

CacheDirLevels 5

CacheDirLength 3





CacheEnable mem /

MCacheSize 4096

MCacheMaxObjectCount 100

MCacheMinObjectSize 1

MCacheMaxObjectSize 2048

In the first module we have defined where the content is to be cached, ie at
'/var/www/cache'. Then we enabled the caching option; defined the directory
level, ie the depth of the directory; and finally the number of characters in a
subdirectory name. In the second module, ie mod_mem_cache, we first enabled the
caching option then defined the size of cache inside the memory. Next, we
defined the maximum objects that can be stored in the memory and the min and max
size of the object. This has to be defined so that the memory is correctly used
else caching a single file of 1 GB in memory can't be considered. Finally, you
enabled all the caching options in Apache. For cases where the page is not
cached and is served directly from the server, you can implement the Deflate
module. It is a data compression algorithm that uses the combination of LZ77
algorithm and Huffman coding.

This will help you in case your content is being downloaded directly from the
server. The content is first compressed then sent to clients, which makes data
transfer faster over the network. Before we start, check whether the Deflate
module is installed or not. For checking, use the same method as used for
mod_cache. If the module is not installed, download the Deflate module rpm from
rpmfind.net and install it in the same way as you installed other modules. Once
the module has been installed, copy the following line inside the 'Location' tag
in the httpd.conf file:

AddOutputFilterByType DEFLATE text/html text/plain
text/xml

This will enable Apache to compress all HTML and XML files. But if you want
to enable compression for other types of data such as images and scripts, into
Apache, then type the following lines as well:

AddOutputFilterByType DEFLATE text/plain

AddOutputFilterByType DEFLATE text/xml

AddOutputFilterByType DEFLATE application/xhtml+xml

AddOutputFilterByType DEFLATE text/css

AddOutputFilterByType DEFLATE application/xml

AddOutputFilterByType DEFLATE image/svg+xml

AddOutputFilterByType DEFLATE application/rss+xml

AddOutputFilterByType DEFLATE application/atom_xml

AddOutputFilterByType DEFLATE application/x-javascript

AddOutputFilterByType DEFLATE application/x-httpd-php

AddOutputFilterByType DEFLATE application/x-httpd-fastphp

AddOutputFilterByType DEFLATE application/x-httpd-eruby

AddOutputFilterByType DEFLATE text/html

Finally you have a full set of solutions in place for serving web pages
faster to the clients. Apart from this, there are directives to optimize
mod_cache. For example CacheMaxFileSize and CacheMinFileSize help you in
defining the minimum and maximum file size that needs to be cached on the disk.
The syntax would be (numbers specified in bytes):

CacheMaxFileSize 20000

CacheMinFileSize 2000

MCacheMaxStreamingBuffer is another such directive for mod_mem_ cache. This
can be used when there is some streaming data to be cached. As you cant predict
the size of the data being streamed, you inadvertently end up having falling
short on cache. Using this directive you can specify the maximum size of the
buffer for streaming data. So the moment the buffer gets full, it discards any
further data; hence you are spared of having your cache space getting saturated.
This is useful as the streamed data doesn't have Content-Length header which
tells the size of the data. Syntax for implemenging the buffer is,
'MCacheMaxStreamingBuffer 10000.'