PHP Programming/Caching

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Templates PHP Programming
Caching
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A cache is a collection of duplicate data, where the original data is expensive to fetch or compute (usually in terms of access time) relative to the cache. In PHP caching is used to minimize page generation time. PHP basically has two main types of caching: 'output caching' and 'parser caching'. PHP 'output caching' saves a chunk of data somewhere that can later be read by another script faster than it can generate it. 'Parser caching' is specific feature. PHP is a scripting language and code is not compiled or optimized to a particular computer. Every PHP file must be parsed and that takes time. This type of time minimization is 'parser caching'.

Contents

Parser cachingEdit

Include cachingEdit

Example:

File:class.test.php

 <?php
 class test{
  function hello(){
     echo "Hello world!\n";
  }
 }
 echo "Class loaded\n"; ?>

File:program.php

 <?php
 require_once("class.test.php");
 $obj1 = new test;
 $obj1->hello();
 require_once("class.test.php");
 $obj2 = new test;
 $obj2->hello(); ?>

output:

Class loaded
Hello world!
Hello world!

Array cachingEdit

Example:

File:program.php

 <?php
 global $sum_cache; 
 $sum_cache=array();
 function sum($nr){
  global $sum_cache;
  if($sum_cache[$nr])
   {
   echo "sum(".$nr.")=".$sum_cache[$nr]." from cache\n";
   return $sum_cache[$nr];
   }
  if($nr<=0)
   {
   $sum_cache[$nr]=0;
   }
  else
   {
   $sum_cache[$nr]+=sum($nr-1)+$nr;
   }
  echo "sum(".$nr.")=".$sum_cache[$nr]." computed\n";
  return $sum_cache[$nr];
  }
 sum(3);
 sum(4);
 ?>

output:

sum(0)=0 computed
sum(1)=1 computed
sum(2)=3 computed
sum(3)=6 computed
sum(3)=6 from cache
sum(4)=10 computed

Session cachingEdit

example:

file:program.php

 <?php
 session_start();
 function find_my_name()
  {
  //perhaps some time-consuming database queries
  return "Bill"; 
  }
 if(isset($_SESSION["hello"]))
  {
  echo "cached\n";
  session_destroy();
  }
 else
  {
  echo "computed\n";
  $_SESSION["hello"]="My Name is ".find_my_name().".\n";
  }
 echo $_SESSION["hello"];
 ?>

output:

computed
My Name is Bill.

output after refresh:

cached
My Name is Bill.

Shared variablesEdit

Example

file:program.php

 <?php
 class test{
  var $list=array();
  function load_list()
   {
   //some less timeconsuming database querys
   $this->list[0]["info"]="small info nr 1";
   $this->list[1]["info"]="small info nr 2";
   $this->list[2]["info"]="small info nr 3";
   }
  function load_element_detail(&$data){
   //some very timeconsuming database querys
   $data["big"]="added big info, maybe structure of objects";
   }
  function get_element($nr){
   return $this->list[$nr];
   }
  function print_element($nr){
   echo "\$this->list[".$nr."][\"info\"]=\"".$this->list[$nr]["info"]."\"\n";
   echo "\$this->list[".$nr."][\"big\"]=\"".$this->list[$nr]["big"]."\"\n";
   }
  }
 $obj = new test;
 $obj->load_list();
 $obj->print_element(0);
 $element=&$obj->get_element(0);
 $obj->load_element_detail($element);
 $obj->print_element(0);
 ?>

output:

$this->list[0]["info"]="small info nr 1"
$this->list[0]["big"]=""
$this->list[0]["info"]="small info nr 1"
$this->list[0]["big"]="added big info, maybe structure of objects"

Output CachingEdit

The server cache policy is included into HTTP header, visible with cURL:

curl -I http://example.org
  Templates PHP Programming
Caching
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