---
title: "Connection Pooling (Microsoft Drivers for PHP for SQL Server) | Microsoft Docs"
ms.custom: ""
ms.date: "08/01/2018"
ms.prod: sql
ms.prod_service: connectivity
ms.reviewer: ""
ms.technology: connectivity
ms.topic: conceptual
helpviewer_keywords: 
  - "connection pooling support"
ms.assetid: 4d9a83d4-08de-43a1-975c-0a94005edc94
author: David-Engel
ms.author: v-daenge
---
# Connection Pooling (Microsoft Drivers for PHP for SQL Server)
[!INCLUDE[Driver_PHP_Download](../../includes/driver_php_download.md)]

The following are important points to note about connection pooling in the [!INCLUDE[ssDriverPHP](../../includes/ssdriverphp_md.md)]:  
  
-   The [!INCLUDE[ssDriverPHP](../../includes/ssdriverphp_md.md)] uses ODBC connection pooling.  
  
-   By default, connection pooling is enabled in Windows. In Linux and macOS, connections are pooled only if connection pooling is enabled for ODBC (see [Enabling/Disabling connection pooling](#enablingdisabling-connection-pooling)). When connection pooling is enabled and you connect to a server, the driver attempts to use a pooled connection before it creates a new one. If an equivalent connection is not found in the pool, a new connection is created and added to the pool. The driver determines whether connections are equivalent based on a comparison of connection strings.  
  
-   When a connection from the pool is used, the connection state is reset.  
  
-   Closing the connection returns the connection to the pool.  
  
For more information about connection pooling, see [Driver Manager Connection Pooling](../../odbc/reference/develop-app/driver-manager-connection-pooling.md).  
  
## Enabling/Disabling connection pooling
### Windows
You can force the driver to create a new connection (instead of looking for an equivalent connection in the connection pool) by setting the value of the *ConnectionPooling* attribute in the connection string to **false** (or 0).  
  
If the *ConnectionPooling* attribute is omitted from the connection string or if it is set to **true** (or 1), the driver only creates a new connection if an equivalent connection does not exist in the connection pool.  
  
For information about other connection attributes, see [Connection Options](../../connect/php/connection-options.md).  
### Linux and macOS
The *ConnectionPooling* attribute cannot be used to enable/disable connection pooling. 

Connection pooling can be enabled/disabled by editing the odbcinst.ini configuration file. The driver should be reloaded for the changes to take effect.

Setting `Pooling` to `Yes` and a positive `CPTimeout` value in the odbcinst.ini file enables connection pooling. 
```
[ODBC]
Pooling=Yes

[ODBC Driver 13 for SQL Server]
CPTimeout=<int value>
```
  
Minimally, the odbcinst.ini file should look something like this example:

```
[ODBC]
Pooling=Yes

[ODBC Driver 13 for SQL Server]
Description=Microsoft ODBC Driver 13 for SQL Server
Driver=/opt/microsoft/msodbcsql/lib64/libmsodbcsql-13.1.so.3.0
UsageCount=1
CPTimeout=120
```

Setting `Pooling` to `No` in the odbcinst.ini file forces the driver to create a new connection.
```
[ODBC]
Pooling=No
```

## Remarks
- In Linux or macOS, all connections will be pooled if pooling is enabled in the odbcinst.ini file. This means the ConnectionPooling connection option has no effect. To disable pooling, set Pooling=No in the odbcinst.ini file and reload the drivers.
  - unixODBC <= 2.3.4 (Linux and macOS) might not return proper diagnostic information, such as error messages, warnings and informative messages
  - for this reason, SQLSRV and PDO_SQLSRV drivers might not be able to properly fetch long data (such as xml, binary) as strings. Long data can be fetched as streams as a workaround. See the example below for SQLSRV.

```
<?php
$connectionInfo = array("Database"=>"test", "UID"=>"username", "PWD"=>"password");

$conn1 = sqlsrv_connect("servername", $connectionInfo);

$longSample = str_repeat("a", 8500);
$xml1 = 
'<ParentXMLTag>
  <ChildTag01>'.$longSample.'</ChildTag01>
</ParentXMLTag>';

// Create table and insert xml string into it
sqlsrv_query($conn1, "CREATE TABLE xml_table (field xml)");
sqlsrv_query($conn1, "INSERT into xml_table values ('$xml1')");

// retrieve the inserted xml
$column1 = getColumn($conn1);

// return the connection to the pool
sqlsrv_close($conn1);

// This connection is from the pool
$conn2 = sqlsrv_connect("servername", $connectionInfo);
$column2 = getColumn($conn2);

sqlsrv_query($conn2, "DROP TABLE xml_table");
sqlsrv_close($conn2);

function getColumn($conn)
{
    $tsql = "SELECT * from xml_table";
    $stmt = sqlsrv_query($conn, $tsql);
    sqlsrv_fetch($stmt);
    // This might fail in Linux and macOS
    // $column = sqlsrv_get_field($stmt, 0, SQLSRV_PHPTYPE_STRING(SQLSRV_ENC_CHAR));
    // The workaround is to fetch it as a stream
    $column = sqlsrv_get_field($stmt, 0, SQLSRV_PHPTYPE_STREAM(SQLSRV_ENC_CHAR));
    sqlsrv_free_stmt($stmt);
    return ($column);
}
?>
```


## See Also  
[How to: Connect Using Windows Authentication](../../connect/php/how-to-connect-using-windows-authentication.md)

[How to: Connect Using SQL Server Authentication](../../connect/php/how-to-connect-using-sql-server-authentication.md)