msphpsql: Connection pooling does not work within Linux

We have just installed the latest SQL 13 drivers and the latest sqlsrv and sqlsrv_pdo PHP extensions. Connection pooling does not seem to be working.

• OS: CentOS 7.2
• PHP: PHP 7.0.12
• SQL Driver: ODBC Driver 13 for SQL Server

Summary of test: We created a test script which will connect to the DB. After the script executes the connection is closed, confirmed by the DB.

odbcinst.ini:

[ODBC]
Pooling = Yes

[ODBC Driver 13 for SQL Server]
Description=Microsoft ODBC Driver 13 for SQL Server
Driver=/opt/microsoft/msodbcsql/lib64/libmsodbcsql-13.0.so.1.0
UsageCount=1
CPTimeout=120

Test script which includes some timing:

$startTime = microtime(true);
function printElapsedTimeSinceLastEvent($event=''){
	global $startTime;
	$elapsed = microtime(true) - $startTime;
	echo $event . round($elapsed*1000) ."\n";
	$startTime = microtime(true);
}

// Connection sqlsrv driver
$pdo = new PDO ("sqlsrv:server=10.12.12.123;database=aDatabaseName",'coolUser','someAwesomePassword');
printElapsedTimeSinceLastEvent("Connected: ");
$stmt = $pdo->prepare("SELECT TOP 10 * FROM users");
$stmt->execute();
printElapsedTimeSinceLastEvent("Execute: ");
$array = $stmt->fetchAll(PDO::FETCH_ASSOC);
printElapsedTimeSinceLastEvent("Fetch: ");

3 consecutive outputs of script:

Connected: 149
Execute: 109
Fetch: 2

Connected: 149
Execute: 100
Fetch: 2

Connected: 152
Execute: 108
Fetch: 2

Using SQL Studio and running EXEC sp_who2 we can see the connections are closed after each run. Using sqlsrv on Windows does keep connections open as expected and does show up in sp_who2 output.

On Windows where we confirmed connection pooling does exist the connection time is significantly faster as one would expect with connection pooling.