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.
Classification
[edit | edit source ]PHP provides several cache systems[1] :
| Name | Data stored | Flush |
|---|---|---|
| Instance cache | PHP object. Ex:if (null === $x) { $x = 1; } |
Restart the script (ex: refresh the Web page). |
| Session cache | PHP object[2] | Empty the navigator cookies. |
| OPcache | Opcode [3] | opcache_reset(); |
| APCu | RAM users variables[4] | apc_clear_cache(); |
| Navigator cache | Rendering | CTRL + F5 |
| ESI | Web page parts | Depends on the CDN or proxy server used. |
| Framework cache | Configurations, translations | Example of Symfony: php bin/console cache:clear empty the temporary var/cache files.
|
| Proxy | Entire web pages | For examples, see: Varnish, HAProxy. |
| NoSQL database | Key-value pairs | For examples, see: Memcached, Redis. |
| ORM cache | Annotations, SQL requests or their results | Example with Doctrine:
php bin/console doctrine:cache:clear-metadata php bin/console doctrine:cache:clear-query php bin/console doctrine:cache:clear-result or: bin/console cache:pool:clear doctrine.query_cache_pool doctrine.result_cache_pool doctrine.system_cache_pool |
| Chain cache | Everything | Use each included cache flushes. |
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'.
Parser caching
[edit | edit source ]Include caching
[edit | edit source ]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 caching
[edit | edit source ]Example:
File:program.php
<?php global $sum_cache; $sum_cache=array(); function sum($nr) { global $sum_cache; if (isset($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 caching
[edit | edit source ]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 variables
[edit | edit source ]Example:
file:program.php
<?php class test { var $list = array(); function load_list() { // some less time consuming database queries $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 time consuming database queries $data["big"] = "added big info, maybe structure of objects"; } function get_element($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 Caching
[edit | edit source ]The server cache policy is included into HTTP header, visible with cURL (with option "I" for header):
curl-Ihttp://example.org
Example:
curl-Ihttps://en.wikibooks.org/ HTTP/2301 date:Sun,02Jan202211:50:58GMT server:mw1429.eqiad.wmnet x-content-type-options:nosniff p3p:CP="See https://en.wikibooks.org/wiki/Special:CentralAutoLogin/P3P for more info." vary:Accept-Encoding,X-Forwarded-Proto,Cookie,Authorization cache-control:s-maxage=1200,must-revalidate,max-age=0 last-modified:Sun,02Jan202211:50:58GMT location:https://en.wikibooks.org/wiki/Main_Page content-length:0 content-type:text/html;charset=utf-8 age:1139 x-cache:cp3062miss,cp3060hit/4 x-cache-status:hit-front server-timing:cache;desc="hit-front",host;desc="cp3060" strict-transport-security:max-age=106384710;includeSubDomains;preload report-to:{"group":"wm_nel","max_age":86400,"endpoints":[{"url":"https://intake-logging.wikimedia.org/v1/events?stream=w3c.reportingapi.network_error&schema_uri=/w3c/reportingapi/network_error/1.0.0"}]} nel:{"report_to":"wm_nel","max_age":86400,"failure_fraction":0.05,"success_fraction":0.0} permissions-policy:interest-cohort=() set-cookie:WMF-Last-Access=02-Jan-2022;Path=/;HttpOnly;secure;Expires=Thu,03Feb202212:00:00GMT set-cookie:WMF-Last-Access-Global=02-Jan-2022;Path=/;Domain=.wikibooks.org;HttpOnly;secure;Expires=Thu,03Feb202212:00:00GMT
References
[edit | edit source ]