<?php
/**
* ADOdb Load Balancer
*
* ADOdbLoadBalancer is a class that allows the user to do read/write splitting
* and load balancing across multiple servers. It can handle and load balance
* any number of write capable (AKA: master) or readonly (AKA: slave) connections,
* including dealing with connection failures and retrying queries on a different
* connection instead.
*
* This file is part of ADOdb, a Database Abstraction Layer library for PHP.
*
* @package ADOdb
* @link https://adodb.org Project's web site and documentation
* @link https://github.com/ADOdb/ADOdb Source code and issue tracker
*
* The ADOdb Library is dual-licensed, released under both the BSD 3-Clause
* and the GNU Lesser General Public Licence (LGPL) v2.1 or, at your option,
* any later version. This means you can use it in proprietary products.
* See the LICENSE.md file distributed with this source code for details.
* @license BSD-3-Clause
* @license LGPL-2.1-or-later
*
* @copyright 2016 Mike Benoit and the ADOdb community
*/
/**
* Class ADOdbLoadBalancer
*/
class ADOdbLoadBalancer
{
/**
* @var bool Once a write or readonly connection is made, stick to that connection for the entire request.
*/
public $enable_sticky_sessions = true;
/**
* @var bool|array All connections to each database.
*/
protected $connections = [];
/**
* @var bool|array Just connections to the write capable database.
*/
protected $connections_write = [];
/**
* @var bool|array Just connections to the readonly database.
*/
protected $connections_readonly = [];
/**
* @var array Counts of all connections and their types.
*/
protected $total_connections = array('all' => 0, 'write' => 0, 'readonly' => 0);
/**
* @var array Weights of all connections for each type.
*/
protected $total_connection_weights = array('all' => 0, 'write' => 0, 'readonly' => 0);
/**
* @var bool When in transactions, always use this connection.
*/
protected $pinned_connection_id = false;
/**
* @var array Last connection_id for each database type.
*/
protected $last_connection_id = array('write' => false, 'readonly' => false, 'all' => false);
/**
* @var bool Session variables that must be maintained across all connections, ie: SET TIME ZONE.
*/
protected $session_variables = [];
/**
* @var bool Called immediately after connecting to any DB.
*/
protected $user_defined_session_init_sql = [];
/**
* Defines SQL queries that are executed each time a new database connection is established.
*
* @param $sql
* @return bool
*/
public function setSessionInitSQL($sql)
{
$this->user_defined_session_init_sql[] = $sql;
return true;
}
/**
* Adds a new database connection to the pool, but no actual connection is made until its needed.
*
* @param $obj
* @return bool
* @throws Exception
*/
public function addConnection($obj)
{
if ($obj instanceof ADOdbLoadBalancerConnection) {
$this->connections[] = $obj;
end($this->connections);
$i = key($this->connections);
$this->total_connections[$obj->type]++;
$this->total_connections['all']++;
$this->total_connection_weights[$obj->type] += abs($obj->weight);
$this->total_connection_weights['all'] += abs($obj->weight);
if ($obj->type == 'write') {
$this->connections_write[] = $i;
} else {
$this->connections_readonly[] = $i;
}
return true;
}
throw new Exception('Connection object is not an instance of ADOdbLoadBalancerConnection');
}
/**
* Removes a database connection from the pool.
*
* @param $i
* @return bool
*/
public function removeConnection($i)
{
if (isset($this->connections[$i])) {
$obj = $this->connections[ $i ];
$this->total_connections[ $obj->type ]--;
$this->total_connections['all']--;
$this->total_connection_weights[ $obj->type ] -= abs($obj->weight);
$this->total_connection_weights['all'] -= abs($obj->weight);
if ($obj->type == 'write') {
unset($this->connections_write[array_search($i, $this->connections_write)]);
// Reindex array.
$this->connections_write = array_values($this->connections_write);
} else {
unset($this->connections_readonly[array_search($i, $this->connections_readonly)]);
// Reindex array.
$this->connections_readonly = array_values($this->connections_readonly);
}
// Remove any sticky connections as well.
if ($this->last_connection_id[$obj->type] == $i) {
$this->last_connection_id[$obj->type] = false;
}
unset($this->connections[$i]);
return true;
}
return false;
}
/**
* Returns a database connection of the specified type.
*
* Takes into account the connection weight for load balancing.
*
* @param string $type Type of database connection, either: 'write' capable or 'readonly'
* @return bool|int|string
*/
public function getConnectionByWeight($type)
{
if ($type == 'readonly') {
$total_weight = $this->total_connection_weights['all'];
} else {
$total_weight = $this->total_connection_weights['write'];
}
$i = false;
if (is_array($this->connections)) {
$n = 0;
$num = mt_rand(0, $total_weight);
foreach ($this->connections as $i => $connection_obj) {
if ($connection_obj->weight > 0 && ($type == 'readonly' || $connection_obj->type == 'write')) {
$n += $connection_obj->weight;
if ($n >= $num) {
break;
}
}
}
}
return $i;
}
/**
* Returns the proper database connection when taking into account sticky sessions and load balancing.
*
* @param $type
* @return bool|int|mixed|string
*/
public function getLoadBalancedConnection($type)
{
if ($this->total_connections == 0) {
$connection_id = 0;
} else {
if ($this->enable_sticky_sessions == true && $this->last_connection_id[$type] !== false) {
$connection_id = $this->last_connection_id[$type];
} else {
if ($type == 'write' && $this->total_connections['write'] == 1) {
$connection_id = $this->connections_write[0];
} else {
$connection_id = $this->getConnectionByWeight($type);
}
}
}
return $connection_id;
}
/**
* Returns the ADODB connection object by connection_id.
*
* Ensures that it's connected and the session variables are executed.
*
* @param $connection_id
* @return bool|ADOConnection
* @throws Exception
*/
public function getConnectionById($connection_id)
{
if (isset($this->connections[$connection_id])) {
$connection_obj = $this->connections[$connection_id];
/** @var ADOConnection $adodb_obj */
$adodb_obj = $connection_obj->getADOdbObject();
if (is_object($adodb_obj) && $adodb_obj->_connectionID == false) {
try {
if ($connection_obj->persistent_connection == true) {
$adodb_obj->Pconnect(
$connection_obj->host,
$connection_obj->user,
$connection_obj->password,
$connection_obj->database
);
} else {
$adodb_obj->Connect(
$connection_obj->host,
$connection_obj->user,
$connection_obj->password,
$connection_obj->database
);
}
} catch (Exception $e) {
// Connection error, see if there are other connections to try still.
throw $e; // No connections left, reThrow exception so application can catch it.
}
// Check to see if a connection test callback was defined, and if so execute it.
// This is useful for testing replication lag and such to ensure the connection is suitable to be used.
$test_connection_callback = $connection_obj->getConnectionTestCallback();
if (is_callable($test_connection_callback)
&& $test_connection_callback($connection_obj, $adodb_obj) !== TRUE
) {
return false;
}
if (is_array($this->user_defined_session_init_sql)) {
foreach ($this->user_defined_session_init_sql as $session_init_sql) {
$adodb_obj->Execute($session_init_sql);
}
}
$this->executeSessionVariables($adodb_obj);
}
return $adodb_obj;
} else {
throw new Exception('Unable to return Connection object...');
}
}
/**
* Returns the ADODB connection object by database type.
*
* Ensures that it's connected and the session variables are executed.
*
* @param string $type
* @param null $pin_connection
* @return ADOConnection|bool
* @throws Exception
*/
public function getConnection($type = 'write', $pin_connection = null)
{
while (($type == 'write' && $this->total_connections['write'] > 0)
|| ($type == 'readonly' && $this->total_connections['all'] > 0)
) {
if ($this->pinned_connection_id !== false) {
$connection_id = $this->pinned_connection_id;
} else {
$connection_id = $this->getLoadBalancedConnection($type);
}
if ($connection_id !== false) {
try {
$adodb_obj = $this->getConnectionById($connection_id);
if (is_object($adodb_obj)) {
break; //Found valid connection, continue with it.
} else {
throw new Exception('ADODB Connection Object does not exist. Perhaps LoadBalancer Database Connection Test Failed?');
}
} catch (Exception $e) {
// Connection error, see if there are other connections to try still.
$this->removeConnection($connection_id);
if ( ($type == 'write' && $this->total_connections['write'] == 0)
|| ($type == 'readonly' && $this->total_connections['all'] == 0)
) {
throw $e;
}
}
} else {
throw new Exception('Connection ID is invalid!');
}
}
if (!isset($connection_id)) {
throw new Exception('No connection available to use at this time! Type: ' . $type);
}
$this->last_connection_id[$type] = $connection_id;
if ($pin_connection === true) {
$this->pinned_connection_id = $connection_id;
} elseif ($pin_connection === false && $adodb_obj->transOff <= 1) {
// UnPin connection only if we are 1 level deep in a transaction.
$this->pinned_connection_id = false;
// When unpinning connection, reset last_connection_id so readonly
// queries don't get stuck on the write capable connection.
$this->last_connection_id['write'] = false;
$this->last_connection_id['readonly'] = false;
}
return $adodb_obj;
}
/**
* This is a hack to work around pass by reference error.
*
* Parameter 1 to ADOConnection::GetInsertSQL() expected to be a reference,
* value given in adodb-loadbalancer.inc.php on line 83
*
* @param $arr
* @return array
*/
private function makeValuesReferenced($arr)
{
$refs = array();
foreach ($arr as $key => $value) {
$refs[$key] = &$arr[$key];
}
return $refs;
}
/**
* Allow setting session variables that are maintained across connections.
*
* Its important that these are set using name/value, so it can determine
* if the same variable is set multiple times causing bloat/clutter when
* new connections are established. For example if the time_zone is set to
* many different ones through the course of a single connection, a new
* connection should only set it to the most recent value.
*
* @param $name
* @param $value
* @param bool $execute_immediately
* @return array|bool|mixed
* @throws Exception
*/
public function setSessionVariable($name, $value, $execute_immediately = true)
{
$this->session_variables[$name] = $value;
if ($execute_immediately == true) {
return $this->executeSessionVariables();
} else {
return true;
}
}
/**
* Executes the session variables on a given ADODB object.
*
* @param ADOConnection|bool $adodb_obj
* @return array|bool|mixed
* @throws Exception
*/
private function executeSessionVariables($adodb_obj = false)
{
if (is_array($this->session_variables) && count($this->session_variables) > 0) {
$sql = '';
foreach ($this->session_variables as $name => $value) {
// $sql .= 'SET SESSION '. $name .' '. $value;
// MySQL uses: SET SESSION foo_bar='foo'
// PGSQL uses: SET SESSION foo_bar 'foo'
// So leave it up to the user to pass the proper value with '=' if needed.
// This may be a candidate to move into ADOdb proper.
$sql .= 'SET SESSION ' . $name . ' ' . $value;
}
if ($adodb_obj !== false) {
return $adodb_obj->Execute($sql);
} else {
return $this->ClusterExecute($sql);
}
}
return false;
}
/**
* Executes the same SQL QUERY on the entire cluster of connections.
* Would be used for things like SET SESSION TIME ZONE calls and such.
*
* @param $sql
* @param bool $inputarr
* @param bool $return_all_results
* @param bool $existing_connections_only
* @return array|bool|mixed
* @throws Exception
*/
public function clusterExecute(
$sql,
$inputarr = false,
$return_all_results = false,
$existing_connections_only = true
) {
if (is_array($this->connections) && count($this->connections) > 0) {
foreach ($this->connections as $key => $connection_obj) {
if ($existing_connections_only == false
|| ($existing_connections_only == true
&& $connection_obj->getADOdbObject()->_connectionID !== false
)
) {
$adodb_obj = $this->getConnectionById($key);
if (is_object($adodb_obj)) {
$result_arr[] = $adodb_obj->Execute($sql, $inputarr);
}
}
}
if (isset($result_arr) && $return_all_results == true) {
return $result_arr;
} else {
// Loop through all results checking to see if they match, if they do return the first one
// otherwise return an array of all results.
if (isset($result_arr)) {
foreach ($result_arr as $result) {
if ($result == false) {
return $result_arr;
}
}
return $result_arr[0];
} else {
// When using lazy connections, there are cases where
// setSessionVariable() is called early on, but there are
// no connections to execute the queries on yet.
// This captures that case and forces a RETURN TRUE to occur.
// As likely the queries will be executed as soon as a
// connection is established.
return true;
}
}
}
return false;
}
/**
* Determines if a SQL query is read-only or not.
*
* @param string $sql SQL Query to test.
* @return bool
*/
public function isReadOnlyQuery($sql)
{
if ( stripos($sql, 'SELECT') === 0
&& stripos($sql, 'FOR UPDATE') === false
&& stripos($sql, ' INTO ') === false
&& stripos($sql, 'LOCK IN') === false
) {
return true;
}
return false;
}
/**
* Use this instead of __call() as it significantly reduces the overhead of call_user_func_array().
*
* @param $sql
* @param bool $inputarr
* @return array|bool|mixed
* @throws Exception
*/
public function execute($sql, $inputarr = false)
{
$type = 'write';
$pin_connection = null;
// Prevent leading spaces from causing isReadOnlyQuery/stripos from failing.
$sql = trim($sql);
// SELECT queries that can write and therefore must be run on a write capable connection.
// SELECT ... FOR UPDATE;
// SELECT ... INTO ...
// SELECT .. LOCK IN ... (MYSQL)
if ($this->isReadOnlyQuery($sql) == true) {
$type = 'readonly';
} elseif (stripos($sql, 'SET') === 0) {
// SET SQL statements should likely use setSessionVariable() instead,
// so state is properly maintained across connections, especially when they are lazily created.
return $this->ClusterExecute($sql, $inputarr);
}
$adodb_obj = $this->getConnection($type, $pin_connection);
if ($adodb_obj !== false) {
return $adodb_obj->Execute($sql, $inputarr);
}
return false;
}
/**
* Magic method to intercept method and callback to the proper ADODB object for write/readonly connections.
*
* @param string $method ADODB method to call.
* @param array $args Arguments to the ADODB method.
* @return bool|mixed
* @throws Exception
*/
public function __call($method, $args)
{
$type = 'write';
$pin_connection = null;
// Intercept specific methods to determine if they are read-only or not.
$method = strtolower($method);
switch ($method) {
// case 'execute': // This is the direct overloaded function above instead.
case 'getone':
case 'getrow':
case 'getall':
case 'getcol':
case 'getassoc':
case 'selectlimit':
if ($this->isReadOnlyQuery(trim($args[0])) == true) {
$type = 'readonly';
}
break;
case 'cachegetone':
case 'cachegetrow':
case 'cachegetall':
case 'cachegetcol':
case 'cachegetassoc':
case 'cacheexecute':
case 'cacheselect':
case 'pageexecute':
case 'cachepageexecute':
$type = 'readonly';
break;
// case 'ignoreerrors':
// // When ignoreerrors is called, PIN to the connection until its called again.
// if (!isset($args[0]) || (isset($args[0]) && $args[0] == FALSE)) {
// $pin_connection = TRUE;
// } else {
// $pin_connection = FALSE;
// }
// break;
// Manual transactions
case 'begintrans':
case 'settransactionmode':
$pin_connection = true;
break;
case 'rollbacktrans':
case 'committrans':
$pin_connection = false;
break;
// Smart transactions
case 'starttrans':
$pin_connection = true;
break;
case 'completetrans':
case 'failtrans':
// getConnection() will only unpin the transaction if we're exiting the last nested transaction
$pin_connection = false;
break;
// Functions that don't require any connection and therefore
// shouldn't force a connection be established before they run.
case 'qstr':
case 'escape':
case 'binddate':
case 'bindtimestamp':
case 'setfetchmode':
case 'setcustommetatype':
$type = false; // No connection necessary.
break;
// Default to assuming write connection is required to be on the safe side.
default:
break;
}
if ($type === false) {
if (is_array($this->connections) && count($this->connections) > 0) {
foreach ($this->connections as $key => $connection_obj) {
$adodb_obj = $connection_obj->getADOdbObject();
return call_user_func_array(array($adodb_obj, $method), $this->makeValuesReferenced($args)); // Just makes the function call on the first object.
}
}
} else {
$adodb_obj = $this->getConnection($type, $pin_connection);
if (is_object($adodb_obj)) {
$result = call_user_func_array(array($adodb_obj, $method), $this->makeValuesReferenced($args));
return $result;
}
}
return false;
}
/**
* Magic method to proxy property getter calls back to the proper ADODB object currently in use.
*
* @param $property
* @return mixed
* @throws Exception
*/
public function __get($property)
{
if (is_array($this->connections) && count($this->connections) > 0) {
foreach ($this->connections as $key => $connection_obj) {
// Just returns the property from the first object.
return $connection_obj->getADOdbObject()->$property;
}
}
return false;
}
/**
* Magic method to proxy property setter calls back to the proper ADODB object currently in use.
*
* @param $property
* @param $value
* @return mixed
* @throws Exception
*/
public function __set($property, $value)
{
// Special function to set object properties on all objects
// without initiating a connection to the database.
if (is_array($this->connections) && count($this->connections) > 0) {
foreach ($this->connections as $key => $connection_obj) {
$connection_obj->getADOdbObject()->$property = $value;
}
return true;
}
return false;
}
/**
* Override the __clone() magic method.
*/
private function __clone()
{
}
}
/**
* Class ADOdbLoadBalancerConnection
*/
class ADOdbLoadBalancerConnection
{
/**
* @var bool ADOdb drive name.
*/
protected $driver = false;
/**
* @var bool ADODB object.
*/
protected $adodb_obj = false;
/**
* @var callable Closure
*/
protected $connection_test_callback = NULL;
/**
* @var string Type of connection, either 'write' capable or 'readonly'
*/
public $type = 'write';
/**
* @var int Weight of connection, lower receives less queries, higher receives more queries.
*/
public $weight = 1;
/**
* @var bool Determines if the connection persistent.
*/
public $persistent_connection = false;
/**
* @var string Database connection host
*/
public $host = '';
/**
* @var string Database connection user
*/
public $user = '';
/**
* @var string Database connection password
*/
public $password = '';
/**
* @var string Database connection database name
*/
public $database = '';
/**
* ADOdbLoadBalancerConnection constructor to setup the ADODB object.
*
* @param $driver
* @param string $type
* @param int $weight
* @param bool $persistent_connection
* @param string $argHostname
* @param string $argUsername
* @param string $argPassword
* @param string $argDatabaseName
*/
public function __construct(
$driver,
$type = 'write',
$weight = 1,
$persistent_connection = false,
$argHostname = '',
$argUsername = '',
$argPassword = '',
$argDatabaseName = ''
) {
if ($type !== 'write' && $type !== 'readonly') {
return false;
}
$this->adodb_obj = ADONewConnection($driver);
$this->type = $type;
$this->weight = $weight;
$this->persistent_connection = $persistent_connection;
$this->host = $argHostname;
$this->user = $argUsername;
$this->password = $argPassword;
$this->database = $argDatabaseName;
return true;
}
/**
* Anonymous function that is called and must return TRUE for the connection to be usable.*
* The first argument is the type of connection to test.
* Useful to check things like replication lag.
* @param callable $callback
* @return void
*/
function setConnectionTestCallback($callback) {
$this->connection_test_callback = $callback;
}
/**
* @return callable|null
*/
function getConnectionTestCallback() {
return $this->connection_test_callback;
}
/**
* Returns the ADODB object for this connection.
*
* @return bool
*/
public function getADOdbObject()
{
return $this->adodb_obj;
}
}