Download - [Developer Shed Network] Server Side - PHP - Caching With PHP Cache_Lite

7/30/2019 [Developer Shed Network] Server Side - PHP - Caching With PHP Cache_Lite

1/24

Caching With PHP Cache_Lite

By icarus

This article copyright Melonfire 2000-2002. All rights reserved.


2/24


3/24

Table of Contents

.................. 1The Need For Speed

................... 2The Food Chain

.................. 3Return Of The Jedi

................... 5Digging Deeper

.................... 7In And Out

................... 9Different Strokes

................... 10Bits And Bytes

................. 12Of Form And Function

................. 14No News Is Good News

.................... 16Cache Cow

..................... 20Endgame

Printed from DevShed.com

i


4/24


5/24

The Need For Speed

In the old days, a Web site usually consisted of static HTML pages and perhaps a few images to liven up

the text. No more is this the case - sophisticated interfaces, streaming media, dynamically-generated

content and other enhancements have all contributed to make todays Web more content-rich andinteractive than ever before. Most often, this is a Good Thing - greater accessibility and more quality

content only make the Web more attractive to new users, and increase its usefulness to the community at

large.

However, there is a downside to this phenomenon as well. As sites become more content-rich, as their

reliance on dynamic data sources increases, as their servers struggle to meet the thousands of requests

coming in per minute, its only natural that the first casualty be the performance of the system. This is

clearly visible in the Web, which today more closely resembles a slow traffic jam than a fast-moving

freeway.

Fortunately, there is a workaround, one that has been successfully used by many sites to provide a

performance improvement: caching. And over the course of this article, Im going to show you a few

examples of this technique in action, using my favourite language, PHP, and an open-source

implementation of a server-side cache called Cache_Lite. Flip the page, and lets get started!


1


6/24

The Food Chain

According to one definition (http://www.nottm.edu.org.uk/techi/networks/caching.pdf), a cache "is a store

of information that is designed to improve the accessibility or availability of data to the user." Simply put,

it is a location where copies of information are kept so they can sent to the user quickly and withoutwastage of already scarce Internet resources.

Now, caches can be maintained at various levels depending on the requirements of the user. Unknown to

many, the most commonly used caching mechanism is the Web browser itself. Modern Web browsers

download content to a temporary location on the hard drive before rendering it to the user. And usually, if

you visit the same page again, the browser will just pick it up from the local cache.

At a workplace, its highly likely that you share your Internet connection with a large group of users. Here,

the local cache of the Web browser does not always help to optimize the utilization of resources. In such a

situation, network administrators often utilize the caching features of the proxy server used to share the

Internet connection. This allows them to ensure that commonly-accessed sites are cached at the time of the

first request. Subsequent requests to the same page are directly serviced from the proxy servers cache. Of

course, this is not advisable for Web sites with highly dynamic content; proxy servers can be configured to

avoid caching these pages.

The above caching mechanism is often replicated at different levels. It is not uncommon to find ISPs

caching content in order to reduce traffic that might otherwise eat up precious bandwidth on the Internet

backbones.

Finally, Web sites often implement complex caching mechanisms so as to serve their own content faster.

This is the type of caching that this article discusses - caching your data at the application level. Keep

reading.


2


7/24

Return Of The Jedi

The Cache_Lite class comes courtesy of PEAR, the PHP Extension and Application Repository

(http://pear.php.net). In case you didnt know, PEAR is an online repository of free PHP software,

including classes and modules for everything from data archiving to XML parsing. When you install PHP,a whole bunch of PEAR modules get installed as well; the Cache_Lite class is one of them.

In case your PHP distribution didnt include Cache_Lite, you can get yourself a copy from the official

PEAR Web site, at http://pear.php.net- simply unzip the distribution archive into your PEAR directory and

youre ready to roll!

Lets begin with something simple - building a primitive cache using Cache_Lite object methods. Heres

the code:


3
http://pear.php.net/http://pear.php.net/


8/24

Dont worry if it didnt make too much sense - all will be explained shortly. For the moment, just feast

your eyes on the output:

Do, or do not. There is no try. -- Yoda, Star Wars

Now refresh the page - you should see something like this, indicating that the second occurrence of the

page has been retrieved from the cache.

Do, or do not. There is no try. -- Yoda, Star Wars [cached]

Lets take a closer look at how this was accomplished, on the next page.


4


9/24

Digging Deeper

When implementing a cache for your Web page, the first step is, obviously, to include the Cache_Lite

class

You can either provide an absolute path to this file, or do what most lazy programmers do - include the

path to your PEAR installation in PHPs "include_path" variable, so that you can access any of the PEAR

classes without needing to type in long, convoluted file paths.

The Cache_Lite object can support multiple caches simultaneously, so long as every cache created has a

unique identifier. In this case, Ive used the identifier "starwars" to uniquely distinguish the cache Ill beusing.

Next, an object of the Cache_Lite class needs to be initialized, and assigned to a PHP variable.

This variable, $objCache, now serves as the control point for cache manipulation.

The constructor of the Cache_Lite class can be provided with an associative array containing

configuration parameters; these parameters allow you to customize the behaviour of the cache. In the

example above, this array contains two parameters, "cacheDir", which specifies the directory used by the

cache, and "lifeTime", which specifies the period for which data should be cached, in seconds.


10/24

?>

Note that the directory specified must already exist, or else the cache will simply not work.

Once an instance of the Cache_Lite object has been created, the business logic to use it becomes fairly

simple. The first step is to check if the required data already exists in the cache. If it doesnt, it should be

generated from the original data source, and a copy saved to the cache for future use. If it does, you can do

something useful with it - write it to a file, pipe it to an external program or - as Ive done here - simply

output it to the screen for all to admire.

Most of this logic is accomplished via the get() and save() methods of the Cache_Lite object. The get()

method checks to see if the data exists in the cache and returns it if so, while the save() method saves data

to the cache. The save() method accepts the data to be saved, together with a unique identifier, as input

arguments; the get() method uses this identifier to find and retrieve the cached data.

The steps above make up a fairly standard process for using the Cache_Lite class, and youll see them

being repeated over and over again in subsequent examples as well.


6


11/24

In And Out

The example you just saw cached the output of PHP statements. Its also possible to cache static HTML

content, through creative use of PHPs output buffering functions. Consider the following example, which

revises the code on the previous page to cache HTML markup instead of PHP command output:

Do, or do not. There is no try.

-- Yoda, Star Wars


12/24

ob_end_flush();

}

?>

In this case, PHPs output buffering functions have been used to capture all the output generated

subsequent to the call to ob_start(), and store this output in a buffer. Once the entire output has been

captured, the ob_get_contents() function is used to retrieve the buffer contents to a variable. This variable

(which now contains the entire HTML page) is then stored in the cache for future use. Finally, the

ob_end_flush() function is used to end output buffering and send the contents of the buffer to the browser.


8


13/24

Different Strokes

An alternative method to accomplish the task on the previous page lies with the Cache_Lite_Output()

class, a subclass of the Cache_Lite class. This subclass (which internally uses output buffering) inherits all

of the attributes of the parent class, and adds two methods to the parent class method collection: a start()method, which begins caching data, and an end() method, which marks the end of data caching.

Consider the following variant of the example on the previosu page, which illustrates how this may be

used:

Do or do not. There is no try.

-- Yoda, Star Wars

Over here, if the call to start() - which is provided with a cache identifier - returns true, it implies that therequested data has already been cached, and the Cache_Lite_Output object takes care of printing the

contents of the cache. If, however, the call to start() returns false, it implies that the data is not present in

the cache, and so all subsequent output generated by the script will be cached, until the objects end()

method is invoked.


9


14/24

Bits And Bytes

Its also possible to use the Cache_Lite object to cache certain sections of a page, rather than the entire

page - useful if some parts of the page are updated more frequently than others. This is accomplished by

specifying a different cache identifier for each block of data that is to be cached, and using these differentidentifiers to retrieve data when needed. Data that is not to be cached (that is, data that is to be retrieved

from source every time it is needed) will simply not be included in the call to the Cache_Lite objects

save() method.

Consider the following example, which demonstrates:


15/24

// second data block

// test if there is a valid cache for this block

if ($data = $objCache->get("featured_character"))

{

// if so, display itecho $data;

}

else

{

// formulate and execute query

$query = "SELECT char FROM characters ORDER BY RAND() LIMIT 1";

$result = mysql_query($query) or die("Error in query: " .

mysql_error());

// get record

$row = mysql_fetch_object($result);

// display it

echo $row->char;// and also cache it

$objCache->save($row->char, "featured_character");

}

// close connection

mysql_close($connection);

?>

In this case, the code for the header and footer blocks is cached; however, the data in between the two is

not. Note the use of two different cache identifiers in this example, one for each block.


11


16/24

Of Form And Function

Just as you can cache HTML markup and PHP command output, its also possible to cache the output of

user-defined functions with the Cache_Lite class...or, more precisely, with the Cache_Lite_Function

subclass. This subclass inherits all the methods and properties of the parent Cache_Lite class, and adds anadditional one: the call() method, which is used to save the return value of a PHP function to the cache.

Using the Cache_Lite_Function objects call() method is simplicity itself: the methods accepts the name of

the function to be cached as its first argument, and input parameters to that function as additional

arguments. It then first checks the cache to see if the function has been cached previously. If it has, the

previous return value is retrieved without actually executing the function; if it has not, the function is

executed (with appropriate arguments) and the result returned to the caller and simultaneously saved to the

cache for future use.

Heres a simple example which demonstrates how this works:

And heres an example of the output:

The cached time is 13:08:50. The real time is 13:11:40


12


17/24

As you might imagine, this class has the potential to do much more than

simply confuse users in search of the time. Flip the page to see what I

mean.


13


18/24

No News Is Good News

Heres another, more realistic example, which caches a database result

set and uses the cached set in order to reduce the time spent on

executing subsequent queries for the same data. The result set isobtained via a function called get_headlines(), converted into a PHP

array and cached using the call() method of the Cache_Lite_Function

class.


19/24

// iterate over return value and print elements

echo "";

foreach($data as $h)

{

echo "$h";}

echo "";

?>

Heres what the output looks like:


15


20/24

Cache Cow

Now that you know the theory, lets wrap this tutorial up with a

real-world example of how useful the Cache_Lite class can be in

improving performance on your Web site. As you may (or may not) know,Amazon.com recently opened up their product catalog, allowing

developers to create Amazon-backed online stores with their new AWS

service. This service allows develoeprs to interact with Amazon.coms

catalog and transaction system using SOAP, and it represents an

important milestone in the progress of XML-based Web services.

The only problem? Querying the AWS system, retrieving XML-encoded data

and formatting it for use on a Web page is a complex process, one which

can affect the performance of your store substantially. In order to

compensate for this, clever developers can consider caching some of the

AWS data on their local systems, reducing the need to query Amazon.com

for every single request and thereby improving performance on their

site.

Heres the script,


21/24

$proxy = $soapclient->getProxy();

// set up an array containing input parameters to be

// passed to the remote procedure

$params = array(

browse_node => 1000,page => 1,

mode => books,

tag => melonfire-20,

type => lite,

devtag => YOUR_TOKEN_HERE,

sort => +salesrank

);

// invoke the method

$result = $proxy->BrowseNodeSearchRequest($params);

// check for errors

if ($result[faultstring])

{echo $result[faultstring];

}

else

{

// no errors?

$total = $result[TotalResults];

$items = $result[Details];

// format and display the results

?>

Bestsellers

Browse the catalog below:


17


22/24


23/24

Im assuming here that you already know how to use AWS (in case you

dont, flip the page for some links to tutorials that will teach you

the basics, and remember that youll need a free AWS developer token

for the script above to work) and instead will focus on the caching

aspects of the system.

Since this Web page contains intermingled HTML and PHP code, its

convenient to use the Cache_Lite_Output class here. The first task,

obviously, is to initialize and configure the cache; Ive set the cache

to refresh itself at 30-minute intervals, since this seems like a

reasonable period of time. Next, Ive used the start() method to see ifany data already exists in the cache, and display it if so.

If no data exists, the NuSOAP PHP class is include()-d in the script, a

SOAP client is instantiated, and a request is made to Amazon.com to

obtain a list of bestsellers (node ID 100 in the AWS system). The

response is then parsed and formatted into a Web page suitable for

display; it is also simultaneously saved to the cache so that future

requests for the same page can be served instantly, without having to

query the AWS system each time. The end result: faster responses to

user clicks, and an overall enhancement in user perception of your

sites performance.


19


24/24

Endgame

And thats about all we have time for. In this article, I introduced

you to the PEAR Cache_Lite class, a PHP class designed specifically to

provide a robust caching mechanism for Web pages. I showed you how toconfigure the location and the lifetime of the cache, and demonstrated

how to use the class to cache both static HTML content and dynamic PHP

output. I also gave you a quick tour of the Cache_Lite class two

variants, the Cache_Lite_Output and Cache_Lite_Function classes,

illustrating how they could be used to cache blocks of output and

function return values, respectively. Finally, I wrapped things up with

a real-world example, showing you how a cache can make a substantial

difference when dealing with complex, XML-based applications like

Amazon Web Services.

In case youd like to learn more about the topics discussed in this

article, you should consider visiting the following links:

Documentation for the PEAR Cache_Lite class, at

http://pear.php.net/package-info.php?pacid=99

phpCache, a lightweight alternative to Cache_Lite, at

http://0x00.org/php/phpCache/, and a tutorial on how to use it, at

http://www.sitepoint.com/article/685

A comprehensive resource on the topic of Web caching, at

http://www.web-caching.com/

An article discussing the benefits of caching your Web content, at

http://www.ariadne.ac.uk/issue4/caching/

Using Amazon Web Services With PHP And SOAP, at

http://www.melonfire.com/community/columns/trog/article.php?id=162

Until next time...stay healthy!Note: Examples are illustrative only, and are not meant for a

production environment. Melonfire provides no warranties or support for

the source code described in this article. YMMV!
http://www.ariadne.ac.uk/issue4/caching/http://www.ariadne.ac.uk/issue4/caching/