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File: backendExample.inc.php

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  Classes of Colin McKinnon  >  Item Cache  >  backendExample.inc.php  >  Download  
File: backendExample.inc.php
Role: Class source
Content type: text/plain
Description: Integrating a backend I/O processor using MySQL
Class: Item Cache
Store values in cache with underflow and overflow
Author: By
Last change:
Date: 4 years ago
Size: 2,930 bytes
 

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Class file image Download
<?php
/**
 * @author Colin McKinnon
 * @licence LGPL version 3
 * @package item cache
 *
 * example of underflow/overflow handlers for itemCache
 *
 * e.g.
 *
 * $h = new ic_backend('localhost','user','s3cr3t','main.keystore');
 * list($overflow, $underflow)=$h->getHandlers();
 * $ic = new itemCache(200, $overflow, 10, $underflow);
 *
 * while ($r=fetch_input_set()) {
 * $r['lookup']=$ic->get($r['key']);
 * if ($r['lookup']==null) {
 * // i.e. the database set is not complete either...
 * $r['lookup']=go_fetch_value_using_expensive_lookup('$r['key']);
 * $ic->add($r['key'], $r['lookup']);
 * // NB the implicit true flag ensures the data will be written back
 * // when evicted
 * }
 * write_output_set($r);
 * }
 * $ic->flush();
 * exit;
 *
 * Of course a really efficient solution might benefit from using a
 * second instance of itemCache to handle the I/O on the input set
 * to batch write operations.
 *
 */
class ic_backend {
    private
$dbh;
    private
$tableref;

    public function
__construct($mysql_host, $mysql_user, $mysql_pass, $mysql_tableref)
    {
       
$this->dbh=mysql_connect($mysql_host, $mysql_user, $mysql_pass);
        if (!
$this->dbh) {
           
trigger_error('Failed to conect to database: ' . mysql_error());
        }
       
$this->tableref=$mysql_tableref;
    }

    public function
getHandlers()
    {
        return array(
           
'overflow'=>array($this, 'overflow'),
           
'underflow'=>array($this, 'underflow'));
    }
 
/**
   * @param mixed $key
   * @param object $itemCache
   *
   * It's the responsibility of the handler to insert the entry
   * into the cache.
   */
   
public function underflow($key, $itemCache)
    {
       
$mykey=mysql_real_escape_string($key, $this->dbh);
       
$qry="SELECT value FROM ' . $this->tableref . ' WHERE key='$mykey' LIMIT 0,1";
       
$result=mysql_query($qry, $this->dbh);
        if (
$result) {
            if (
$row=mysql_fetch_assoc($result)) {
               
$itemCache->add($key, $row['value'], false);
               
// NB the false flag tells the cache not to write this
                // value back when evicted
           
} else {
               
/* Currently failed lookup (also missing from the database)
                 * is not cacheable, but we might want to make it cacheable
                 * e.g.
                 * $itemCache->add($key, null);
                 */
           
}
        } else {
           
trigger_error('Error fetching data: ' . mysql_error());
        }
    }
 
/**
   * @param array $data - array of ($key1=>$val1, $key2=>$val2....)
   *
   * invoked from itemCache
   */
   
public function overflow($data)
    {
       
$qry="INSERT IGNORE INTO " . $this->tableref . " (key, value) ";
       
$join=' VALUES ';
        foreach (
$data as $key=>$val) {
           
$qry.=$join . "('" . mysql_real_escape_string($key, $this->dbh)
                .
"','" . mysql_real_escape_string($value, $this->dbh) . "')";
           
$join=',';
        }
        if (!
mysql_query($qry, $this->dbh)) {
           
trigger_error('Failed inserting data: ' . mysql_error());
        }
    }
}