Spanner/src/Database.php
public function close()
    {
        if ($this->session) {
            if ($this->sessionPool) {
                $this->sessionPool->release($this->session);
            } else {
                $this->session->delete();
            }

            $this->session = null;
        }
    }
public function close()
    {
        if ($this->session) {
            if ($this->sessionPool) {
                $this->sessionPool->release($this->session);
            } else {
                $this->session->delete();
            }

            $this->session = null;
        }
    }
public function close ( ) { if ( $ this -> session ) { if ( $ this -> sessionPool ) { $ this -> sessionPool -> release ( $ this -> session ) ; } else { $ this -> session -> delete ( ) ; } $ this -> session = null ; } }
Closes the database connection by returning the active session back to
the session pool queue or by deleting the session if there is no pool
associated.

It is highly important to ensure this is called as it is not always safe
to rely soley on {@see Google\Cloud\Spanner\Database::__destruct()}.

Example:
```
$database->close();
```
Closes the database connection by returning the active session back to the session pool queue or by deleting the session if there is no pool associated .