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db_load_balancer.php
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Wed, Jun 25, 11:43 AM

db_load_balancer.php
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<?php
/**
* @version $Id: db_load_balancer.php 14934 2011-12-28 18:06:28Z alex $
* @package In-Portal
* @copyright Copyright (C) 1997 - 2011 Intechnic. All rights reserved.
* @license GNU/GPL
* In-Portal is Open Source software.
* This means that this software may have been modified pursuant
* the GNU General Public License, and as distributed it includes
* or is derivative of works licensed under the GNU General Public License
* or other free or open source software licenses.
* See http://www.in-portal.org/license for copyright notices and details.
*/
defined('FULL_PATH') or die('restricted access!');
class kDBLoadBalancer extends kBase {
/**
* Current database type
*
* @var string
* @access protected
*/
protected $dbType = 'mysql';
/**
* Function to handle sql errors
*
* @var string
* @access public
*/
public $errorHandler = '';
/**
* Database connection settings
*
* @var Array
* @access protected
*/
protected $servers = Array ();
/**
* Load of each slave server, given
*
* @var Array
* @access protected
*/
protected $serverLoads = Array ();
/**
* Caches replication lag of servers
*
* @var Array
* @access protected
*/
protected $serverLagTimes = Array ();
/**
* Connection references to opened connections
*
* @var Array
* @access protected
*/
protected $connections = Array ();
/**
* Index of last user slave connection
*
* @var int
* @access protected
*/
protected $slaveIndex = false;
/**
* Index of the server, that was used last
*
* @var int
* @access protected
*/
protected $lastUsedIndex = 0;
/**
* Consider slave down if it isn't responding for N milliseconds
*
* @var int
* @access protected
*/
protected $DBClusterTimeout = 10;
/**
* Scale load balancer polling time so that under overload conditions, the database server
* receives a SHOW STATUS query at an average interval of this many microseconds
*
* @var int
* @access protected
*/
protected $DBAvgStatusPoll = 2000;
/**
* Indicates, that next database query could be cached, when memory caching is enabled
*
* @var bool
* @access public
*/
public $nextQueryCachable = false;
/**
* Indicates, that next query should be sent to maser database
*
* @var bool
*/
public $nextQueryFromMaster = false;
/**
* Creates new instance of load balancer class
*
* @param string $dbType
* @param Array|string $errorHandler
*/
function __construct($dbType, $errorHandler = '')
{
parent::__construct();
$this->dbType = $dbType;
$this->errorHandler = $errorHandler;
$this->DBClusterTimeout *= 1e6; // convert to milliseconds
}
/**
* Setups load balancer according given configuration
*
* @param Array $config
* @return void
* @access public
*/
public function setup($config)
{
$this->servers = Array ();
$this->servers[0] = Array (
'DBHost' => $config['Database']['DBHost'],
'DBUser' => $config['Database']['DBUser'],
'DBUserPassword' => $config['Database']['DBUserPassword'],
'DBName' => $config['Database']['DBName'],
'DBLoad' => 0,
);
if ( isset($config['Databases']) ) {
$this->servers = array_merge($this->servers, $config['Databases']);
}
foreach ($this->servers as $server_index => $server_setting) {
$this->serverLoads[$server_index] = $server_setting['DBLoad'];
}
}
/**
* Returns connection index to master database
*
* @return int
* @access protected
*/
protected function getMasterIndex()
{
return 0;
}
/**
* Returns connection index to slave database. This takes into account load ratios and lag times.
* Side effect: opens connections to databases
*
* @return int
* @access protected
*/
protected function getSlaveIndex()
{
if ( count($this->servers) == 1 || $this->Application->isAdmin ) {
// skip the load balancing if there's only one server OR in admin console
return 0;
}
elseif ( $this->slaveIndex !== false ) {
// shortcut if generic reader exists already
return $this->slaveIndex;
}
$total_elapsed = 0;
$non_error_loads = $this->serverLoads;
$i = $found = $lagged_slave_mode = false;
// first try quickly looking through the available servers for a server that meets our criteria
do {
$current_loads = $non_error_loads;
$overloaded_servers = $total_threads_connected = 0;
while ($current_loads) {
if ( $lagged_slave_mode ) {
// when all slave servers are too lagged, then ignore lag and pick random server
$i = $this->pickRandom($current_loads);
}
else {
$i = $this->getRandomNonLagged($current_loads);
if ( $i === false && $current_loads ) {
// all slaves lagged -> pick random lagged slave then
$lagged_slave_mode = true;
$i = $this->pickRandom( $current_loads );
}
}
if ( $i === false ) {
// all slaves are down -> use master as a slave
$this->slaveIndex = $this->getMasterIndex();
return $this->slaveIndex;
}
$conn =& $this->openConnection($i);
if ( !$conn ) {
unset($non_error_loads[$i], $current_loads[$i]);
continue;
}
// Perform post-connection backoff
$threshold = isset($this->servers[$i]['DBMaxThreads']) ? $this->servers[$i]['DBMaxThreads'] : false;
$backoff = $this->postConnectionBackoff($conn, $threshold);
if ( $backoff ) {
// post-connection overload, don't use this server for now
$total_threads_connected += $backoff;
$overloaded_servers++;
unset( $current_loads[$i] );
}
else {
// return this server
break 2;
}
}
// no server found yet
$i = false;
// if all servers were down, quit now
if ( !$non_error_loads ) {
break;
}
// back off for a while
// scale the sleep time by the number of connected threads, to produce a roughly constant global poll rate
$avg_threads = $total_threads_connected / $overloaded_servers;
usleep($this->DBAvgStatusPoll * $avg_threads);
$total_elapsed += $this->DBAvgStatusPoll * $avg_threads;
} while ( $total_elapsed < $this->DBClusterTimeout );
if ( $i !== false ) {
// slave connection successful
if ( $this->slaveIndex <= 0 && $this->serverLoads[$i] > 0 && $i !== false ) {
$this->slaveIndex = $i;
}
}
return $i;
}
/**
* Returns random non-lagged server
*
* @param Array $loads
* @return int
* @access protected
*/
protected function getRandomNonLagged($loads)
{
// unset excessively lagged servers
$lags = $this->getLagTimes();
foreach ($lags as $i => $lag) {
if ( $i != 0 && isset($this->servers[$i]['DBMaxLag']) ) {
if ( $lag === false ) {
unset( $loads[$i] ); // server is not replicating
}
elseif ( $lag > $this->servers[$i]['DBMaxLag'] ) {
unset( $loads[$i] ); // server is excessively lagged
}
}
}
// find out if all the slaves with non-zero load are lagged
if ( !$loads || array_sum($loads) == 0 ) {
return false;
}
// return a random representative of the remainder
return $this->pickRandom($loads);
}
/**
* Select an element from an array of non-normalised probabilities
*
* @param Array $weights
* @return int
* @access protected
*/
protected function pickRandom($weights)
{
if ( !is_array($weights) || !$weights ) {
return false;
}
$sum = array_sum($weights);
if ( $sum == 0 ) {
return false;
}
$max = mt_getrandmax();
$rand = mt_rand(0, $max) / $max * $sum;
$index = $sum = 0;
foreach ($weights as $index => $weight) {
$sum += $weight;
if ( $sum >= $rand ) {
break;
}
}
return $index;
}
/**
* Get lag time for each server
* Results are cached for a short time in memcached, and indefinitely in the process cache
*
* @return Array
* @access protected
*/
protected function getLagTimes()
{
if ( $this->serverLagTimes ) {
return $this->serverLagTimes;
}
$expiry = 5;
$request_rate = 10;
$cache_key = 'lag_times:' . $this->servers[0]['DBHost'];
$times = $this->Application->getCache($cache_key);
if ( $times ) {
// randomly recache with probability rising over $expiry
$elapsed = adodb_mktime() - $times['timestamp'];
$chance = max(0, ($expiry - $elapsed) * $request_rate);
if ( mt_rand(0, $chance) != 0 ) {
unset( $times['timestamp'] );
$this->serverLagTimes = $times;
return $times;
}
}
// cache key missing or expired
$times = Array();
foreach ($this->servers as $index => $server) {
if ($index == 0) {
$times[$index] = 0; // master
}
else {
$conn =& $this->openConnection($index);
if ($conn !== false) {
$times[$index] = $conn->getSlaveLag();
}
}
}
// add a timestamp key so we know when it was cached
$times['timestamp'] = adodb_mktime();
$this->Application->setCache($cache_key, $times, $expiry);
// but don't give the timestamp to the caller
unset($times['timestamp']);
$this->serverLagTimes = $times;
return $this->serverLagTimes;
}
/**
* Determines whatever server should not be used, even, when connection was made
*
* @param kDBConnection $conn
* @param int $threshold
* @return int
* @access protected
*/
protected function postConnectionBackoff(&$conn, $threshold)
{
if ( !$threshold ) {
return 0;
}
$status = $conn->getStatus('Thread%');
return $status['Threads_running'] > $threshold ? $status['Threads_connected'] : 0;
}
/**
* Open a connection to the server given by the specified index
* Index must be an actual index into the array.
* If the server is already open, returns it.
*
* On error, returns false.
*
* @param integer $i Server index
* @return kDBConnection|false
* @access protected
*/
protected function &openConnection($i)
{
if ( isset($this->connections[$i]) ) {
$conn =& $this->connections[$i];
}
else {
$server = $this->servers[$i];
$server['serverIndex'] = $i;
$conn =& $this->reallyOpenConnection($server, $i == $this->getMasterIndex());
if ( $conn->connectionOpened ) {
$this->connections[$i] =& $conn;
$this->lastUsedIndex = $i;
}
else {
$conn = false;
}
}
if ( $this->nextQueryCachable && is_object($conn) ) {
$conn->nextQueryCachable = true;
$this->nextQueryCachable = false;
}
return $conn;
}
/**
* Really opens a connection.
* Returns a database object whether or not the connection was successful.
*
* @param Array $server
* @param bool $is_master
* @return kDBConnection
*/
protected function &reallyOpenConnection($server, $is_master)
{
$db =& $this->Application->makeClass( 'kDBConnection', Array ($this->dbType, $this->errorHandler, $server['serverIndex']) );
/* @var $db kDBConnection */
$db->debugMode = $this->Application->isDebugMode();
$db->Connect($server['DBHost'], $server['DBUser'], $server['DBUserPassword'], $this->servers[0]['DBName'], true, !$is_master);
return $db;
}
/**
* Returns first field of first line of recordset if query ok or false otherwise
*
* @param string $sql
* @param int $offset
* @return string
* @access public
*/
public function GetOne($sql, $offset = 0)
{
$conn =& $this->chooseConnection($sql);
return $conn->GetOne($sql, $offset);
}
/**
* Returns first row of recordset if query ok, false otherwise
*
* @param string $sql
* @param int $offset
* @return Array
* @access public
*/
public function GetRow($sql, $offset = 0)
{
$conn =& $this->chooseConnection($sql);
return $conn->GetRow($sql, $offset);
}
/**
* Returns 1st column of recordset as one-dimensional array or false otherwise
* Optional parameter $key_field can be used to set field name to be used as resulting array key
*
* @param string $sql
* @param string $key_field
* @return Array
* @access public
*/
public function GetCol($sql, $key_field = null)
{
$conn =& $this->chooseConnection($sql);
return $conn->GetCol($sql, $key_field);
}
/**
* Queries db with $sql query supplied and returns rows selected if any, false
* otherwise. Optional parameter $key_field allows to set one of the query fields
* value as key in string array.
*
* @param string $sql
* @param string $key_field
* @param bool $no_debug
* @return Array
* @access public
*/
public function Query($sql, $key_field = null, $no_debug = false)
{
$conn =& $this->chooseConnection($sql);
return $conn->Query($sql, $key_field, $no_debug);
}
/**
* Performs sql query, that will change database content
*
* @param string $sql
* @return bool
* @access public
*/
public function ChangeQuery($sql)
{
$conn =& $this->chooseConnection($sql);
return $conn->ChangeQuery($sql);
}
/**
* If it's a string, adds quotes and backslashes (only work since PHP 4.3.0)
* Otherwise returns as-is
*
* @param mixed $string
* @return string
* @access public
*/
public function qstr($string)
{
$conn =& $this->openConnection($this->lastUsedIndex);
return $conn->qstr($string);
}
/**
* Calls "qstr" function for each given array element
*
* @param Array $array
* @param string $function
* @return Array
*/
public function qstrArray($array, $function = 'qstr')
{
$conn =& $this->openConnection($this->lastUsedIndex);
return $conn->qstrArray($array, $function);
}
/**
* Performs insert of given data (useful with small number of queries)
* or stores it to perform multiple insert later (useful with large number of queries)
*
* @param Array $fields_hash
* @param string $table
* @param string $type
* @param bool $insert_now
* @return bool
* @access public
*/
public function doInsert($fields_hash, $table, $type = 'INSERT', $insert_now = true)
{
$conn =& $this->openConnection( $this->getMasterIndex() );
return $conn->doInsert($fields_hash, $table, $type, $insert_now);
}
/**
* Update given field values to given record using $key_clause
*
* @param Array $fields_hash
* @param string $table
* @param string $key_clause
* @return bool
* @access public
*/
public function doUpdate($fields_hash, $table, $key_clause)
{
$conn =& $this->openConnection( $this->getMasterIndex() );
return $conn->doUpdate($fields_hash, $table, $key_clause);
}
/**
* When undefined method is called, then send it directly to last used slave server connection
*
* @param string $name
* @param Array $arguments
* @return mixed
* @access public
*/
public function __call($name, $arguments)
{
$conn =& $this->openConnection($this->lastUsedIndex);
return call_user_func_array( Array (&$conn, $name), $arguments );
}
/**
* Returns appropriate connection based on sql
*
* @param string $sql
* @return kDBConnection
* @access protected
*/
protected function &chooseConnection($sql)
{
if ( $this->nextQueryFromMaster ) {
$this->nextQueryFromMaster = false;
$index = $this->getMasterIndex();
}
else {
$sid = isset($this->Application->Session) ? $this->Application->GetSID() : '9999999999999999999999';
if ( preg_match('/(^[ \t\r\n]*(ALTER|CREATE|DROP|RENAME|DELETE|DO|INSERT|LOAD|REPLACE|TRUNCATE|UPDATE))|ses_' . $sid . '/', $sql) ) {
$index = $this->getMasterIndex();
}
else {
$index = $this->getSlaveIndex();
}
}
$this->lastUsedIndex = $index;
$conn =& $this->openConnection($index);
return $conn;
}
}

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