# 4. Connecting to Oracle Database

Connections between python-oracledb and Oracle Database are used for executing SQL, PL/SQL, and SODA.

By default, python-oracledb runs in a ‘Thin’ mode which connects directly to Oracle Database. This mode does not need Oracle Client libraries. However, some additional functionality is available when python-oracledb uses them. Python-oracledb is said to be in ‘Thick’ mode when Oracle Client libraries are used. See Enabling python-oracledb Thick mode. Both modes have comprehensive functionality supporting the Python Database API v2.0 Specification.

If you intend to use the Thick mode, then you must call `init_oracle_client()` in the application before any standalone connection or pool is created. The python-oracledb Thick mode loads Oracle Client libraries which communicate over Oracle Net to an existing database. The Oracle Client libraries need to be installed separately. See Installing python-oracledb. Oracle Net is not a separate product: it is how the Oracle Client and Oracle Database communicate.

There are two ways to create a connection to Oracle Database using python-oracledb:

- Standalone connections: Standalone connections are useful when the application needs a single connection to a database. Connections are created by calling `oracledb.connect()`.

- Pooled connections: Connection pooling is important for performance when applications frequently connect and disconnect from the database. Pools support Oracle’s high availability features and are recommended for applications that must be reliable. Small pools can also be useful for applications that want a few connections available for infrequent use. Pools are created with `oracledb.create_pool()` at application initialization time, and then `ConnectionPool.acquire()` can be called to obtain a connection from a pool.

Many connection behaviors can be controlled by python-oracledb connection options. Other settings can be configured in Optional Oracle Net Configuration Files or in Optional Oracle Client Configuration File. These include limiting the amount of time that opening a connection can take, or enabling network encryption.

Note

Creating a connection in python-oracledb Thin mode always requires a connection string, or the database host name and service name, to be specified. The Thin mode cannot use “bequeath” connections and does not reference Oracle environment variables `ORACLE_SID`, `TWO_TASK`, or `LOCAL`.

Note

When using python-oracledb in Thin mode, the `tnsnames.ora` file will not be automatically located. The file’s directory must explicitly be passed to the application, see Optional Oracle Net Configuration Files.

## 4.1. Standalone Connections

Standalone connections are database connections that do not use a python-oracledb connection pool. They are useful for simple applications that use a single connection to a database. Simple connections are created by calling `oracledb.connect()` and passing a database username, the database password for that user, and a ‘data source name’ connection string. Python-oracledb also supports external authentication and so passwords do not need to be in the application.

### 4.1.1. Creating a Standalone Connection

Standalone connections are created by calling `oracledb.connect()`.

A simple standalone connection example:

    import oracledb
    import getpass

    userpwd = getpass.getpass("Enter password: ")

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="dbhost.example.com/orclpdb")

You could alternatively read the password from an environment variable:

    userpwd = os.environ.get("PYTHON_PASSWORD")

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="localhost/orclpdb")

The `oracledb.connect()` method allows the database host name and database service name to be passed as separate parameters. The database listener port can also be passed:

    import os

    userpwd = os.environ.get("PYTHON_PASSWORD")

    connection = oracledb.connect(user="hr", password=userpwd,
                                  host="localhost", port=1521, service_name="orclpdb")

If you like to encapsulate values, parameters can be passed using a ConnectParams Object:

    params = oracledb.ConnectParams(host="my_host", port=my_port, service_name="my_service_name")
    conn = oracledb.connect(user="my_user", password="my_password", params=params)

Some values such as the database host name can be specified as `connect()` parameters, as part of the connect string, and in the `params` object. If a `dsn` is passed, the python-oracledb Thick mode will use the `dsn` string to connect. Otherwise, a connection string is internally constructed from the individual parameters and `params` object values, with the individual parameters having precedence. In python-oracledb’s default Thin mode, a connection string is internally used that contains all relevant values specified. The precedence in Thin mode is that values in any `dsn` parameter override values passed as individual parameters, which themselves override values set in the `params` object. Similar precedence rules also apply to other values.

A single, combined connection string can be passed to `connect()` but this may cause complications if the password contains ‘@’ or ‘/’ characters:

    username="hr"
    userpwd = os.environ.get("PYTHON_PASSWORD")
    host = "localhost"
    port = 1521
    service_name = "orclpdb"

    dsn = f'{username}/{userpwd}@{host}:{port}/{service_name}'
    connection = oracledb.connect(dsn)

#### 4.1.1.1. Closing Connections

Connections should be released when they are no longer needed. You may prefer to let connections be automatically cleaned up when references to them go out of scope. This lets python-oracledb close dependent resources in the correct order:

    with oracledb.connect(user="hr", password=userpwd,
                          dsn="dbhost.example.com/orclpdb") as connection:
        with connection.cursor() as cursor:
            cursor.execute("insert into SomeTable values (:1, :2)",
                           (1, "Some string"))
            connection.commit()

This code ensures that once the block is completed, the connection is closed and resources have been reclaimed by the database. In addition, any attempt to use the variable `connection` outside of the block will simply fail.

Alternatively, you can explicitly close a connection by calling. `Connection.close()`:

    connection = oracledb.connect(user="hr", password=userpwd, dsn="localhost/orclpdb")

    # do something with the connection
    . . .

    # close the connection
    connection.close()

### 4.1.2. Common Connection Errors

Some of the common connection errors that you may encounter in the python-oracledb’s default Thin mode are detailed below. Also see Error Handling in Thin and Thick Modes.

#### 4.1.2.1. Use keyword parameters

If you use:

    connection = oracledb.connect("hr", userpwd, "localhost/orclpdb")

then you will get the error:

    TypeError: connect() takes from 0 to 1 positional arguments but 3 were given

The `oracledb.connect()` method requires keyword parameters to be used

    connection = oracledb.connect(user="hr", password=userpwd, dsn="localhost/orclpdb")

The exception passing a single argument containing the combined credential and connection string. This is supported:

    connection = oracledb.connect("hr/userpwd@localhost/orclpdb")

#### 4.1.2.2. Use the correct credentials

If your username or password are not known by the database that you attempted to connect to, then you will get the error:

    ORA-01017: invalid username/password; logon denied

Find the correct username and password and try reconnecting.

#### 4.1.2.3. Use the correct connection string

If the hostname, port, or service name are incorrect, then the connection will fail with the error:

    DPY-6001: cannot connect to database. Service "doesnotexist" is not
    registered with the listener at host "localhost" port 1521. (Similar to
    ORA-12514)

This error means that Python successfully reached a computer (in this case, “localhost” using the default port 1521) that is running a database. However, the database service you wanted (“doesnotexist”) does not exist there.

Technically, the error means the listener does not know about the service at the moment. So you might also get this error if the database is currently restarting.

This error is similar to the `ORA-12514` error that you may see when connecting with python-oracledb in Thick mode, or with some other Oracle tools.

The solution is to use a valid service name in the connection string. You can:

- Check and fix any typos in the service name you used

- Check if the hostname and port are correct

- Ask your database administrator (DBA) for the correct values

- Wait a few moments and re-try in case the database is restarting

- Review the connection information in your cloud console or cloud wallet, if you are using a cloud database

- Run lsnrctl status on the database machine to find the known service names

## 4.2. Connection Strings

The data source name parameter `dsn` of `oracledb.connect()` and `oracledb.create_pool()` is the Oracle Database connection string that identifies which database service to connect to. The `dsn` string can be one of:

- An Oracle Easy Connect string

- An Oracle Net Connect Descriptor string

- A Net Service Name mapping to a connect descriptor

For more information about naming methods, see Oracle Net Service Reference.

### 4.2.1. Easy Connect Syntax for Connection Strings

An Easy Connect string is often the simplest connection string to use for the data source name parameter `dsn` of `oracledb.connect()` and `oracledb.create_pool()`. This method does not need configuration files such as `tnsnames.ora`.

For example, to connect to the Oracle Database service `orclpdb` that is running on the host `dbhost.example.com` with the default Oracle Database port 1521, use:

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="dbhost.example.com/orclpdb")

If the database is using a non-default port, it must be specified:

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="dbhost.example.com:1984/orclpdb")

The Easy Connect syntax supports Oracle Database service names. It cannot be used with the older System Identifiers (SID).

The latest Easy Connect Plus syntax allows the use of multiple hosts or ports, along with optional entries for the wallet location, the distinguished name of the database server, and even allows some network configuration options be set. This means that a sqlnet.ora file is not needed for some common connection scenarios.

In python-oracledb Thin mode, any unknown Easy Connect options are ignored and are not passed to the database. See Connection String Differences for more information.

In python-oracledb Thick mode, it is the Oracle Client libraries that parse the Easy Connect string. Check the Easy Connect Naming method in Oracle Net Service Administrator’s Guide for the syntax to use in your version of the Oracle Client libraries.

### 4.2.2. Net Service Names for Connection Strings

Connect Descriptor Strings are commonly stored in a tnsnames.ora file and associated with a Net Service Name. This name can be used directly for the data source name parameter `dsn` of `oracledb.connect()` and `oracledb.create_pool()`. For example, given a file `/opt/oracle/config/tnsnames.ora` with the following contents:

    ORCLPDB =
      (DESCRIPTION =
        (ADDRESS = (PROTOCOL = TCP)(HOST = dbhost.example.com)(PORT = 1521))
        (CONNECT_DATA =
          (SERVER = DEDICATED)
          (SERVICE_NAME = orclpdb)
        )
      )

Then you could connect in python-oracledb Thin mode by using the following code:

    connection = oracledb.connect(user="hr", password=userpwd, dsn="orclpdb",
                                  config_dir="/opt/oracle/config")

More options for how python-oracledb locates `tnsnames.ora` files is detailed in Optional Oracle Net Configuration Files. Note in python-oracledb Thick mode, the configuration directory must be set during initialization, not at connection time.

For more information about Net Service Names, see Database Net Services Reference.

### 4.2.3. Oracle Net Connect Descriptor Strings

Full Connect Descriptor strings can be embedded directly in python-oracledb applications:

    dsn = """(DESCRIPTION=
                 (FAILOVER=on)
                 (ADDRESS_LIST=
                   (ADDRESS=(PROTOCOL=tcp)(HOST=sales1-svr)(PORT=1521))
                   (ADDRESS=(PROTOCOL=tcp)(HOST=sales2-svr)(PORT=1521)))
                 (CONNECT_DATA=(SERVICE_NAME=sales.example.com)))"""

    connection = oracledb.connect(user="hr", password=userpwd, dsn=dsn)

The `oracledb.ConnectParams()` and `ConnectParams.get_connect_string()` functions can be used to construct a connect descriptor string from the individual components, see Using the ConnectParams Builder Class. For example:

    cp = oracledb.ConnectParams(host="dbhost.example.com", port=1521, service_name="orclpdb")
    dsn = cp.get_connect_string()
    print(dsn)

This prints:

    (DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=tcp)(HOST=dbhost.example.com)(PORT=1521)))(CONNECT_DATA=(SERVICE_NAME=orclpdb))(SECURITY=(SSL_SERVER_DN_MATCH=True)))

### 4.2.4. JDBC and Oracle SQL Developer Connection Strings

The python-oracledb connection string syntax is different from Java JDBC and the common Oracle SQL Developer syntax. If these JDBC connection strings reference a service name like:

    jdbc:oracle:thin:@hostname:port/service_name

For example:

    jdbc:oracle:thin:@dbhost.example.com:1521/orclpdb

then use Oracle’s Easy Connect syntax in python-oracledb:

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="dbhost.example.com:1521/orclpdb")

Alternatively, if a JDBC connection string uses an old-style Oracle Database SID “system identifier”, and the database does not have a service name:

    jdbc:oracle:thin:@hostname:port:sid

For example:

    jdbc:oracle:thin:@dbhost.example.com:1521:orcl

then connect by using the `sid` parameter:

    connection = oracledb.connect(user="hr", password=userpwd,
                                  host="dbhost.example.com", port=1521, sid="orcl")

Alternatively, create a `tnsnames.ora` (see Optional Oracle Net Configuration Files) entry, for example:

    finance =
     (DESCRIPTION =
       (ADDRESS = (PROTOCOL = TCP)(HOST = dbhost.example.com)(PORT = 1521))
       (CONNECT_DATA =
         (SID = ORCL)
       )
     )

This can be referenced in python-oracledb:

    connection = oracledb.connect(user="hr", password=userpwd, dsn="finance")

## 4.3. Using the ConnectParams Builder Class

The ConnectParams class allows you to define connection parameters in a single place. The `oracledb.ConnectParams()` function returns a `ConnectParams` object. The object can be passed to `oracledb.connect()`. For example:

    cp = oracledb.ConnectParams(user="hr", password=userpwd,
                                host="dbhost", port=1521, service_name="orclpdb")
    connection = oracledb.connect(params=cp)

The use of the ConnectParams class is optional because you can pass the same parameters directly to `connect()`. For example, the code above is equivalent to:

    connection = oracledb.connect(user="hr", password=userpwd,
                                  host="dbhost", port=1521, service_name="orclpdb")

If you want to keep credentials separate, you can use ConnectParams just to encapsulate connection string components:

    cp = oracledb.ConnectParams(host="dbhost", port=1521, service_name="orclpdb")
    connection = oracledb.connect(user="hr", password=userpwd, params=cp)

You can use `ConnectParams.get_connect_string()` to get a connection string from a ConnectParams object:

    cp = oracledb.ConnectParams(host="dbhost", port="my_port", service_name="my_service_name")
    dsn = cp.get_connect_string()
    connection = oracledb.connect(user="hr", password=userpwd, dsn=dsn)

To parse a connection string and store components as attributes:

    cp = oracledb.ConnectParams()
    cp.parse_connect_string("host.example.com:1522/orclpdb")

Most parameter values of `oracledb.ConnectParams()` are gettable as attributes. For example, to get the stored host name:

    print(cp.host)

Attributes such as the password are not gettable.

You can set individual attributes using `ConnectParams.set()`:

    cp = oracledb.ConnectParams(host="localhost", port=1521, service_name="orclpdb")

    # set a new port
    cp.set(port=1522)

    # change both the port and service name
    cp.set(port=1523, service_name="orclpdb")

Some values such as the database host name can be specified as `oracledb.connect()`, parameters, as part of the connect string, and in the `params` object. If a `dsn` is passed, the python-oracledb Thick mode will use the `dsn` string to connect. Otherwise, a connection string is internally constructed from the individual parameters and `params` object values, with the individual parameters having precedence. In python-oracledb’s default Thin mode, a connection string is internally used that contains all relevant values specified. The precedence in Thin mode is that values in any `dsn` parameter override values passed as individual parameters, which themselves override values set in the `params` object. Similar precedence rules also apply to other values.

## 4.4. Connection Pooling

Python-oracledb’s connection pooling lets applications create and maintain a pool of open connections to the database. Connection pooling is available in both Thin and Thick modes. Connection pooling is important for performance and scalability when applications need to handle a large number of users who do database work for short periods of time but have relatively long periods when the connections are not needed. The high availability features of pools also make small pools useful for applications that want a few connections available for infrequent use and requires them to be immediately usable when acquired.

In python-oracledb Thick mode, the pool implementation uses Oracle’s session pool technology which supports additional Oracle Database features, for example some advanced high availability features.

### 4.4.1. Creating a Connection Pool

A connection pool is created by calling `oracledb.create_pool()`. Various pool options can be specified as described in `create_pool()` and detailed below.

For example, to create a pool that initially contains one connection but can grow up to five connections:

    pool = oracledb.create_pool(user="hr", password=userpwd, dsn="dbhost.example.com/orclpdb",
                                min=1, max=5, increment=1)

After the pool has been created, your application can get a connection from it by calling `ConnectionPool.acquire()`:

    connection = pool.acquire()

These connections can be used in the same way that Standalone Connections are used.

By default, `acquire()` calls wait for a connection to be available before returning to the application. A connection will be available if the pool currently has idle connections, when another user returns a connection to the pool, or after the pool grows. Waiting allows applications to be resilient to temporary spikes in connection load. Users may have to wait a brief time to get a connection but will not experience connection failures.

You can change the behavior of `acquire()` by setting the `getmode` option during pool creation. For example, the option can be set so that if all the connections are currently in use by the application, any additional `acquire()` call will return an error immediately.

    pool = oracledb.create_pool(user="hr", password=userpwd, dsn="dbhost.example.com/orclpdb",
                                min=2, max=5, increment=1,
                                getmode=oracledb.POOL_GETMODE_NOWAIT)

Note that when using this option value in Thick mode with Oracle Client libraries 12.2 or earlier, the `acquire()` call will still wait if the pool can grow. However, you will get an error immediately if the pool is at its maximum size. With newer Oracle Client libraries and with Thin mode, an error will be returned if the pool has to, or cannot, grow.

When your application has finished performing all required database operations, the pooled connection should be released to make it available for other users of the pool. You can do this with `ConnectionPool.release()` or `Connection.close()`. Alternatively you may prefer to let pooled connections be closed implicitly at the end of scope. For example, by using a `with` statement:

    with pool.acquire() as connection:
        with connection.cursor() as cursor:
            for result in cursor.execute("select * from mytab"):
                print(result)

At application shutdown, the connection pool can be completely closed using `ConnectionPool.close()`:

    pool.close()

To force immediate pool termination when connections are still in use, execute:

    pool.close(force=True)

See connection_pool.py for a runnable example of connection pooling.

Connection Pool Growth

At pool creation, `min` connections are established to the database. When a pool needs to grow, new connections are created automatically limited by the `max` size. The pool `max` size restricts the number of application users that can do work in parallel on the database.

The number of connections opened by a pool can shown with the attribute. `ConnectionPool.opened`. The number of connections the application has obtained with `acquire()` can be shown with `ConnectionPool.busy`. The difference in values is the number of connections unused or ‘idle’ in the pool. These idle connections may be candidates for the pool to close, depending on the pool configuration.

Pool growth is normally initiated when `acquire()` is called and there are no idle connections in the pool that can be returned to the application. The number of new connections created internally will be the value of the `create_pool()` parameter `increment`.

Depending on whether Thin or Thick mode is used and on the pool creation `getmode` value that is set, any `acquire()` call that initiates pool growth may wait until all `increment` new connections are internally opened. However, in this case the cost is amortized because later `acquire()` calls may not have to wait and can immediately return an available connection. Some users set larger `increment` values even for fixed-size pools because it can help a pool re-establish itself if all connections become invalid, for example after a network dropout. In the common case of Thin mode with the default `getmode` of `POOL_GETMODE_WAIT`, any `acquire()` call that initiates pool growth will return after the first new connection is created, regardless of how big `increment` is. The pool will then continue to re-establish connections in a background thread.

A connection pool can shrink back to its minimum size when connections opened by the pool are not used by the application. This frees up database resources while allowing pools to retain connections for active users. Note this is currently applicable to Thick mode only. If connections are idle in the pool (i.e. not currently acquired by the application) and are unused for longer than the pool creation attribute `timeout` value , then they will be closed. The default `timeout` is 0 seconds signifying an infinite time and meaning idle connections will never be closed. The pool creation parameter `max_lifetime_session` also allows pools to shrink. This parameter bounds the total length of time that a connection can exist starting from the time the pool created it. If a connection was created `max_lifetime_session` or longer seconds ago, then it will be closed when it is idle in the pool. In the case when `timeout` and `max_lifetime_session` are both set, the connection will be terminated if either the idle timeout happens or the max lifetime setting is exceeded. Note that when using python-oracledb in Thick mode with Oracle Client libraries prior to 21c, pool shrinkage is only initiated when the pool is accessed so pools in fully dormant applications will not shrink until the application is next used.

For pools created with external authentication, with homogeneous set to False, or when using Database Resident Connection Pooling (DRCP), then the number of connections opened at pool creation is zero even if a larger value is specified for `min`. Also, in these cases the pool increment unit is always 1 regardless of the value of `increment`.

Pool Connection Health

Before `ConnectionPool.acquire()` returns, python-oracledb does a lightweight check similar to `Connection.is_healthy()` to see if the network transport for the selected connection is still open. If it is not, then `acquire()` will clean up the connection and return a different one.

This check will not detect cases such as where the database session has been terminated by the DBA, or reached a database resource manager quota limit. To help in those cases, `acquire()` will also do a full round-trip database ping similar to `Connection.ping()` when it is about to return a connection that was idle in the pool (i.e. not currently acquired by the application) for `ConnectionPool.ping_interval` seconds. If the ping fails, the connection will be discarded and another one obtained before `acquire()` returns to the application.

Because this full ping is time based and may not occur for each `acquire()`, the application may still get an unusable connection. Also, network timeouts and session termination may occur between the calls to `acquire()` and `Cursor.execute()`. To handle these cases, applications need to check for errors after each `execute()` and make application-specific decisions about retrying work if there was a connection failure. When using python-oracledb in Thick mode, Oracle Database features like Application Continuity can do this automatically in some cases.

You can explicitly initiate a full round-trip ping at any time with `Connection.ping()` to check connection liveness but the overuse will impact performance and scalability.

Ensure that the firewall, resource manager or user profile IDLE_TIME do not expire idle sessions, since this will require connections to be recreated which will impact performance and scalability.

A pool’s internal connection re-establishment after lightweight and full pings can mask performance-impacting configuration issues such as firewalls terminating connections. You should monitor AWR reports for an unexpectedly large connection rate.

### 4.4.2. Connection Pool Sizing

The Oracle Real-World Performance Group’s recommendation is to use fixed size connection pools. The values of `min` and `max` should be the same. When using older versions of Oracle Client libraries the `increment` parameter will need to be zero (which is internally treated as a value of one), but otherwise you may prefer a larger size since this will affect how the connection pool is re-established after, for example, a network dropout invalidates all connections.

Fixed size pools avoid connection storms on the database which can decrease throughput. See Guideline for Preventing Connection Storms: Use Static Pools, which contains more details about sizing of pools. Having a fixed size will also guarantee that the database can handle the upper pool size. For example, if a dynamically sized pool needs to grow but the database resources are limited, then `ConnectionPool.acquire()` may return errors such as `ORA-28547`. With a fixed pool size, this class of error will occur when the pool is created, allowing you to change the pool size or reconfigure the database before users access the application. With a dynamically growing pool, the error may occur much later while the application is in use.

The Real-World Performance Group also recommends keeping pool sizes small because they may perform better than larger pools. The pool attributes should be adjusted to handle the desired workload within the bounds of available resources in python-oracledb and the database.

### 4.4.3. Connection Pool Reconfiguration

Some pool settings can be changed dynamically with `ConnectionPool.reconfigure()`. This allows the pool size and other attributes to be changed during application runtime without needing to restart the pool or application.

For example a pool’s size can be changed like:

    pool.reconfigure(min=10, max=10, increment=0)

After any size change has been processed, reconfiguration on the other parameters is done sequentially. If an error such as an invalid value occurs when changing one attribute, then an exception will be generated but any already changed attributes will retain their new values.

During reconfiguration of a pool’s size, the behavior of `ConnectionPool.acquire()` depends on the pool creation `getmode` value in effect when `acquire()` is called, see `ConnectionPool.reconfigure()`. Closing connections or closing the pool will wait until after pool reconfiguration is complete.

Calling `reconfigure()` is the only way to change a pool’s `min`, `max` and `increment` values. Other attributes such as `wait_timeout` can be passed to `reconfigure()` or they can be set directly, for example:

    pool.wait_timeout = 1000

### 4.4.4. Session CallBacks for Setting Pooled Connection State

Applications can set “session” state in each connection. Examples of session state are NLS globalization settings from `ALTER SESSION` statements. Pooled connections will retain their session state after they have been released back to the pool. However, because pools can grow or connections in the pool can be recreated, there is no guarantee a subsequent `acquire()` call will return a database connection that has any particular state.

The `create_pool()` parameter `session_callback` enables efficient setting of session state so that connections have a known session state, without requiring that state to be explicitly set after every `acquire()` call. The callback is internally invoked when `acquire()` is called and runs first.

The session callback can be a Python function or a PL/SQL procedure.

Connections can also be tagged when they are released back to the pool. The tag is a user-defined string that represents the session state of the connection. When acquiring connections, a particular tag can be requested. If a connection with that tag is available, it will be returned. If not, then another session will be returned. By comparing the actual and requested tags, applications can determine what exact state a session has, and make any necessary changes.

Connection tagging and PL/SQL callbacks are only available in python-oracledb Thick mode. Python callbacks can be used in python-oracledb Thin and Thick modes.

There are three common scenarios for `session_callback`:

- When all connections in the pool should have the same state, use a Python callback without tagging.

- When connections in the pool require different state for different users, use a Python callback with tagging.

- With Database Resident Connection Pooling (DRCP), use a PL/SQL callback with tagging.

#### 4.4.4.1. Python Callback

If the `session_callback` parameter is a Python procedure, it will be called whenever `acquire()` will return a newly created database connection that has not been used before. It is also called when connection tagging is being used and the requested tag is not identical to the tag in the connection returned by the pool.

An example is:

    # Set the NLS_DATE_FORMAT for a session
    def init_session(connection, requested_tag):
        with connection.cursor() as cursor:
            cursor.execute("alter session set nls_date_format = 'YYYY-MM-DD HH24:MI'")

    # Create the pool with session callback defined
    pool = oracledb.create_pool(user="hr", password=userpwd, dsn="localhost/orclpdb",
                                session_callback=init_session)

    # Acquire a connection from the pool (will always have the new date format)
    connection = pool.acquire()

If needed, the `init_session()` procedure is called internally before `acquire()` returns. It will not be called when previously used connections are returned from the pool. This means that the ALTER SESSION does not need to be executed after every `acquire()` call. This improves performance and scalability.

In this example tagging was not being used, so the `requested_tag` parameter is ignored.

Note that if you need to execute multiple SQL statements in the callback, use an anonymous PL/SQL block to save round-trips of repeated `execute()` calls. With ALTER SESSION, pass multiple settings in the one statement:

    cursor.execute("""
            begin
                execute immediate
                        'alter session set nls_date_format = ''YYYY-MM-DD''
                                           nls_language = AMERICAN';
                -- other SQL statements could be put here
            end;""")

#### 4.4.4.2. Connection Tagging

Connection tagging is used when connections in a pool should have differing session states. In order to retrieve a connection with a desired state, the `tag` attribute in `acquire()` needs to be set.

Note

Connection tagging is only supported in the python-oracledb Thick mode. See Enabling python-oracledb Thick mode .

When python-oracledb is using Oracle Client libraries 12.2 or later, then python-oracledb uses ‘multi-property tags’ and the tag string must be of the form of one or more “name=value” pairs separated by a semi-colon, for example `"loc=uk;lang=cy"`.

When a connection is requested with a given tag, and a connection with that tag is not present in the pool, then a new connection, or an existing connection with cleaned session state, will be chosen by the pool and the session callback procedure will be invoked. The callback can then set desired session state and update the connection’s tag. However, if the `matchanytag` parameter of `acquire()` is True, then any other tagged connection may be chosen by the pool and the callback procedure should parse the actual and requested tags to determine which bits of session state should be reset.

The example below demonstrates connection tagging:

    def init_session(connection, requested_tag):
        if requested_tag == "NLS_DATE_FORMAT=SIMPLE":
            sql = "ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD'"
        elif requested_tag == "NLS_DATE_FORMAT=FULL":
            sql = "ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI'"
        cursor = connection.cursor()
        cursor.execute(sql)
        connection.tag = requested_tag

    pool = oracledb.create_pool(user="hr", password=userpwd, dsn="orclpdb",
                                 session_callback=init_session)

    # Two connections with different session state:
    connection1 = pool.acquire(tag="NLS_DATE_FORMAT=SIMPLE")
    connection2 = pool.acquire(tag="NLS_DATE_FORMAT=FULL")

See session_callback.py for an example.

#### 4.4.4.3. PL/SQL Callback

Note

PL/SQL Callbacks are only supported in the python-oracledb Thick mode. See Enabling python-oracledb Thick mode.

When python-oracledb uses Oracle Client 12.2 or later, the session callback can also be the name of a PL/SQL procedure. A PL/SQL callback will be initiated only when the tag currently associated with a connection does not match the tag that is requested. A PL/SQL callback is most useful when using Database Resident Connection Pooling (DRCP) because DRCP does not require a round-trip to invoke a PL/SQL session callback procedure.

The PL/SQL session callback should accept two VARCHAR2 arguments:

    PROCEDURE myPlsqlCallback (
        requestedTag IN  VARCHAR2,
        actualTag    IN  VARCHAR2
    );

The logic in this procedure can parse the actual tag in the session that has been selected by the pool and compare it with the tag requested by the application. The procedure can then change any state required before the connection is returned to the application from `acquire()`.

If the `matchanytag` attribute of `acquire()` is True, then a connection with any state may be chosen by the pool.

Oracle ‘multi-property tags’ must be used. The tag string must be of the form of one or more “name=value” pairs separated by a semi-colon, for example `"loc=uk;lang=cy"`.

In python-oracledb set `session_callback` to the name of the PL/SQL procedure. For example:

    pool = oracledb.create_pool(user="hr", password=userpwd,
                                 dsn="dbhost.example.com/orclpdb:pooled",
                                 session_callback="MyPlsqlCallback")

    connection = pool.acquire(tag="NLS_DATE_FORMAT=SIMPLE",
                              # DRCP options, if you are using DRCP
                              cclass='MYCLASS',
                              purity=oracledb.ATTR_PURITY_SELF)

See session_callback_plsql.py for an example.

### 4.4.5. Heterogeneous and Homogeneous Connection Pools

By default, connection pools are ‘homogeneous’, meaning that all connections use the same database credentials. Both python-oracledb Thin and Thick modes support homogeneous pools.

Creating Heterogeneous Pools

The python-oracledb Thick mode additionally supports Heterogeneous pools, allowing different user names and passwords to be passed to each `acquire()` call.

To create an heterogeneous pool, set the `create_pool()` parameter `homogeneous` to False:

    pool = oracledb.create_pool(dsn="dbhost.example.com/orclpdb", homogeneous=False)
    connection = pool.acquire(user="hr", password=userpwd)

### 4.4.6. Using the PoolParams Builder Class

The PoolParams class allows you to define connection and pool parameters in a single place. The `oracledb.PoolParams()` function returns a `PoolParams` object. This is a subclass of the ConnectParams class with additional pool-specific attributes such as the pool size. A `PoolParams` object can be passed to `oracledb.create_pool()`. For example:

    pp = oracledb.PoolParams(min=1, max=2, increment=1)
    pool = oracledb.create_pool(user="hr", password=userpw, dsn="dbhost.example.com/orclpdb",
                                params=pp)

The use of the PoolParams class is optional because you can pass the same parameters directly to `create_pool()`. For example, the code above is equivalent to:

    pool = oracledb.create_pool(user="hr", password=userpw, dsn="dbhost.example.com/orclpdb",
                                min=1, max=2, increment=1)

Most PoolParams arguments are gettable as properties. They may be set individually using the `set()` method:

    pp = oracledb.PoolParams()
    pp.set(min=5)
    print(pp.min) # 5

Some values such as the database host name, can be specified as `oracledb.create_pool()` parameters, as part of the connect string, and in the `params` object. If a `dsn` is passed, the python-oracledb Thick mode will use the `dsn` string to connect. Otherwise, a connection string is internally constructed from the individual parameters and `params` object values, with the individual parameters having precedence. In python-oracledb’s default Thin mode, a connection string is internally used that contains all relevant values specified. The precedence in Thin mode is that values in any `dsn` parameter override values passed as individual parameters, which themselves override values set in the `params` object. Similar precedence rules also apply to other values.

## 4.5. Database Resident Connection Pooling (DRCP)

Database Resident Connection Pooling (DRCP) enables database resource sharing for applications which use a large number of connections that run in multiple client processes or run on multiple middle-tier application servers. By default, each connection from Python will use one database server process. DRCP allows pooling of these server processes. This reduces the amount of memory required on the database host. The DRCP pool can be shared by multiple applications.

DRCP is useful for applications which share the same database credentials, have similar session settings (for example date format settings or PL/SQL package state), and where the application gets a database connection, works on it for a relatively short duration, and then releases it.

For efficiency, it is recommended that DRCP connections should be used in conjunction with python-oracledb’s local connection pool. However, although using DRCP with standalone connections is not as efficient it does allow the database to reuse database server processes which can provide a performance benefit for applications that cannot use a local connection pool.

Although applications can choose whether or not to use pooled connections at runtime, care must be taken to configure the database appropriately for the number of expected connections, and also to stop inadvertent use of non-DRCP connections leading to a database server resource shortage. Conversely, avoid using DRCP connections for long-running operations.

For more information about DRCP, see Oracle Database Concepts Guide and for DRCP Configuration, see Oracle Database Administrator’s Guide.

Using DRCP with python-oracledb applications involves the following steps:

1. Configuring and enabling DRCP in the database

2. Configuring the application to use a DRCP connection

3. Deploying the application

### 4.5.1. Enabling DRCP in Oracle Database

Every Oracle Database uses a single, default DRCP connection pool. From Oracle Database 21c, each pluggable database can optionally have its own pool. Note that DRCP is already enabled in Oracle Autonomous Database and pool management is different to the steps below.

DRCP pools can be configured and administered by a DBA using the `DBMS_CONNECTION_POOL` package:

    EXECUTE DBMS_CONNECTION_POOL.CONFIGURE_POOL(
        pool_name => 'SYS_DEFAULT_CONNECTION_POOL',
        minsize => 4,
        maxsize => 40,
        incrsize => 2,
        session_cached_cursors => 20,
        inactivity_timeout => 300,
        max_think_time => 600,
        max_use_session => 500000,
        max_lifetime_session => 86400)

Alternatively, the method `DBMS_CONNECTION_POOL.ALTER_PARAM()` can set a single parameter:

    EXECUTE DBMS_CONNECTION_POOL.ALTER_PARAM(
        pool_name => 'SYS_DEFAULT_CONNECTION_POOL',
        param_name => 'MAX_THINK_TIME',
        param_value => '1200')

The `inactivity_timeout` setting terminates idle pooled servers, helping optimize database resources. To avoid pooled servers permanently being held onto by a selfish Python script, the `max_think_time` parameter can be set. The parameters `num_cbrok` and `maxconn_cbrok` can be used to distribute the persistent connections from the clients across multiple brokers. This may be needed in cases where the operating system per-process descriptor limit is small. Some customers have found that having several connection brokers improves performance. The `max_use_session` and `max_lifetime_session` parameters help protect against any unforeseen problems affecting server processes. The default values will be suitable for most users. See the Oracle DRCP documentation for details on parameters.

In general, if pool parameters are changed, then the pool should be restarted. Otherwise, server processes will continue to use old settings.

There is a `DBMS_CONNECTION_POOL.RESTORE_DEFAULTS()` procedure to reset all values.

When DRCP is used with RAC, each database instance has its own connection broker and pool of servers. Each pool has the identical configuration. For example, all pools start with `minsize` server processes. A single DBMS_CONNECTION_POOL command will alter the pool of each instance at the same time. The pool needs to be started before connection requests begin. The command below does this by bringing up the broker, which registers itself with the database listener:

    EXECUTE DBMS_CONNECTION_POOL.START_POOL()

Once enabled this way, the pool automatically restarts when the database instance restarts, unless explicitly stopped with the `DBMS_CONNECTION_POOL.STOP_POOL()` command:

    EXECUTE DBMS_CONNECTION_POOL.STOP_POOL()

The pool cannot be stopped while connections are open.

### 4.5.2. Coding Applications to use DRCP

To use DRCP, application connection establishment must request a DRCP pooled server. The best practice is also to specify a user-chosen connection class name. A ‘purity’ of the connection session state can optionally be specified. See the Oracle Database documentation on benefiting from scalability for more information on purity and connection classes.

To request the database, use a DRCP pooled server and you can use a specific connection string in `oracledb.create_pool()` or `oracledb.connect()` like one of the following syntaxes.

For example with the Easy Connect syntax:

    dsn = "dbhost.example.com/orcl:pooled"

Alternatively, add `(SERVER=POOLED)` to the connect descriptor such as used in an Oracle Network configuration file `tnsnames.ora`:

    customerpool = (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)
              (HOST=dbhost.example.com)
              (PORT=1521))(CONNECT_DATA=(SERVICE_NAME=CUSTOMER)
              (SERVER=POOLED)))

You can also specify to use a DRCP pooled server by setting the `server_type` parameter when creating a standalone connection or creating a python-oracledb connection pool. For example:

    pool = oracledb.create_pool(user="hr", password=userpwd, dsn="dbhost.example.com/orclpdb",
                                min=2, max=5, increment=1,
                                server_type="pooled")

DRCP Connection Class Names

The best practice is to specify a `cclass` class name when creating a python-oracledb connection pool. This user-chosen name provides some partitioning of DRCP session memory so reuse is limited to similar applications. It provides maximum pool sharing if multiple application processes are started. A class name also allows better DRCP usage tracking in the database. In the database monitoring views, the class name shown will be the value specified in the application prefixed with the user name.

To create a connection pool requesting a DRCP pooled server and specifying a class name you can call:

    pool = oracledb.create_pool(user="hr", password=userpwd, dsn="dbhost.example.com/orclpdb:pooled",
                                min=2, max=5, increment=1,
                                cclass="MYAPP")

The python-oracledb connection pool size does not need to match the DRCP pool size. The limit on overall execution parallelism is determined by the DRCP pool size.

Connection class names can also be passed to `acquire()`, if desired:

    pool = oracledb.create_pool(user="hr", password=userpwd, dsn="dbhost.example.com/orclpdb:pooled",
                                min=2, max=5, increment=1,
                                cclass="MYAPP")

    connection = mypool.acquire(cclass="OTHERAPP")

If a pooled server of a requested class is not available, a server with new session state is used. If the DRCP pool cannot grow, a server with a different class may be used and its session state cleared.

If `cclass` is not set, then the pooled server sessions will not be reused optimally, and the DRCP statistic views may record large values for NUM_MISSES.

DRCP Connection Purity

DRCP allows the connection session memory to be reused or cleaned each time a connection is acquired from the pool. The pool or connection creation `purity` parameter can be one of `PURITY_NEW`, `PURITY_SELF`, or `PURITY_DEFAULT`. The value `PURITY_SELF` allows reuse of both the pooled server process and session memory, giving maximum benefit from DRCP. By default, python-oracledb pooled connections use `PURITY_SELF` and standalone connections use `PURITY_NEW`.

To limit session sharing, you can explicitly require that new session memory be allocated each time `acquire()` is called:

    pool = oracledb.create_pool(user="hr", password=userpwd, dsn="dbhost.example.com/orclpdb:pooled",
                                min=2, max=5, increment=1,
                                cclass="MYAPP", purity=oracledb.PURITY_NEW)

Setting the Connection Class and Purity in the Connection String

For the python-oracledb Thin mode, you can specify the class and purity in the connection string itself. This removes the need to modify an existing application when you want to use DRCP:

    dsn = "localhost/orclpdb:pooled?pool_connection_class=MYAPP&pool_purity=self"

Recent versions of Oracle Client libraries also support this syntax. However, explicitly specifying the purity as SELF in this way may cause some unusable connections in a python-oracledb Thick mode connection pool not to be terminated. In summary, if you cannot programmatically set the class name and purity, or cannot use python-oracledb Thin mode, then avoid explicitly setting the purity as a connection string parameter when using a python-oracledb connection pooling in Thick mode.

Closing Connections when using DRCP

Similar to using a python-oracledb connection pool, Python scripts where python-oracledb connections do not go out of scope quickly (which releases them), or do not currently use `Connection.close()` or `ConnectionPool.release()` should be examined to see if the connections can be closed earlier. This allows maximum reuse of DRCP pooled servers by other users:

    pool = oracledb.create_pool(user="hr", password=userpwd, dsn="dbhost.example.com/orclpdb:pooled",
                                min=2, max=5, increment=1,
                                cclass="MYAPP")

    # Do some database operations
    connection = mypool.acquire()
    . . .
    connection.close();             # <- Add this to release the DRCP pooled server

    # Do lots of non-database work
    . . .

    # Do some more database operations
    connection = mypool.acquire()   # <- And get a new pooled server only when needed
    . . .
    connection.close();

### 4.5.3. Monitoring DRCP

Data dictionary views are available to monitor the performance of DRCP. Database administrators can check statistics such as the number of busy and free servers, and the number of hits and misses in the pool against the total number of requests from clients. The views include:

- `DBA_CPOOL_INFO`

- `V$PROCESS`

- `V$SESSION`

- `V$CPOOL_STATS`

- `V$CPOOL_CC_STATS`

- `V$CPOOL_CONN_INFO`

DBA_CPOOL_INFO View

`DBA_CPOOL_INFO` displays configuration information about the DRCP pool. The columns are equivalent to the `dbms_connection_pool.configure_pool()` settings described in the table of DRCP configuration options, with the addition of a `STATUS` column. The status is `ACTIVE` if the pool has been started and `INACTIVE` otherwise. Note that the pool name column is called `CONNECTION_POOL`. This example checks whether the pool has been started and finds the maximum number of pooled servers:

    SQL> SELECT connection_pool, status, maxsize FROM dba_cpool_info;

    CONNECTION_POOL              STATUS        MAXSIZE
    ---------------------------- ---------- ----------
    SYS_DEFAULT_CONNECTION_POOL  ACTIVE             40

V$PROCESS and V$SESSION Views

The `V$SESSION` view shows information about the currently active DRCP sessions. It can also be joined with `V$PROCESS` through `V$SESSION.PADDR = V$PROCESS.ADDR` to correlate the views.

V$CPOOL_STATS View

The `V$CPOOL_STATS` view displays information about the DRCP statistics for an instance. The V$CPOOL_STATS view can be used to assess how efficient the pool settings are. This example query shows an application using the pool effectively. The low number of misses indicates that servers and sessions were reused. The wait count shows just over 1% of requests had to wait for a pooled server to become available:

    NUM_REQUESTS   NUM_HITS NUM_MISSES  NUM_WAITS
    ------------ ---------- ---------- ----------
           10031      99990         40       1055

If `cclass` was set (allowing pooled servers and sessions to be reused), then NUM_MISSES will be low. If the pool maxsize is too small for the connection load, then NUM_WAITS will be high.

V$CPOOL_CC_STATS View

The view `V$CPOOL_CC_STATS` displays information about the connection class level statistics for the pool per instance:

    SQL> SELECT cclass_name, num_requests, num_hits, num_misses
         FROM v$cpool_cc_stats;

    CCLASS_NAME                      NUM_REQUESTS   NUM_HITS NUM_MISSES
    -------------------------------- ------------ ---------- ----------
    HR.MYCLASS                             100031      99993         38

The class name columns shows the database user name appended with the connection class name.

V$CPOOL_CONN_INFO View

The `V$POOL_CONN_INFO` view gives insight into client processes that are connected to the connection broker, making it easier to monitor and trace applications that are currently using pooled servers or are idle. This view was introduced in Oracle 11gR2.

You can monitor the view `V$CPOOL_CONN_INFO` to, for example, identify misconfigured machines that do not have the connection class set correctly. This view maps the machine name to the class name. In python-oracledb Thick mode, the class name will be default to one like shown below:

    SQL> SELECT cclass_name, machine FROM v$cpool_conn_info;

    CCLASS_NAME                             MACHINE
    --------------------------------------- ------------
    CJ.OCI:SP:wshbIFDtb7rgQwMyuYvodA        cjlinux

In this example, you would examine applications on `cjlinux` and make them set `cclass`.

When connecting to Oracle Autonomous Database on shared infrastructure (ADB-S), the `V$CPOOL_CONN_INFO` view can be used to track the number of connection hits and misses to show the pool efficiency.

## 4.6. Connecting Using Proxy Authentication

Proxy authentication allows a user (the “session user”) to connect to Oracle Database using the credentials of a “proxy user”. Statements will run as the session user. Proxy authentication is generally used in three-tier applications where one user owns the schema while multiple end-users access the data. For more information about proxy authentication, see the Oracle documentation.

An alternative to using proxy users is to set `Connection.client_identifier` after connecting and use its value in statements and in the database, for example for monitoring.

The following proxy examples use these schemas. The `mysessionuser` schema is granted access to use the password of `myproxyuser`:

    CREATE USER myproxyuser IDENTIFIED BY myproxyuserpw;
    GRANT CREATE SESSION TO myproxyuser;

    CREATE USER mysessionuser IDENTIFIED BY itdoesntmatter;
    GRANT CREATE SESSION TO mysessionuser;

    ALTER USER mysessionuser GRANT CONNECT THROUGH myproxyuser;

After connecting to the database, the following query can be used to show the session and proxy users:

    SELECT SYS_CONTEXT('USERENV', 'PROXY_USER'),
           SYS_CONTEXT('USERENV', 'SESSION_USER')
    FROM DUAL;

Standalone connection examples:

    # Basic Authentication without a proxy
    connection = oracledb.connect(user="myproxyuser", password="myproxyuserpw",
                                  dsn="dbhost.example.com/orclpdb")
    # PROXY_USER:   None
    # SESSION_USER: MYPROXYUSER

    # Basic Authentication with a proxy
    connection = oracledb.connect(user="myproxyuser[mysessionuser]", password="myproxyuserpw",
                                  dsn="dbhost.example.com/orclpdb")
    # PROXY_USER:   MYPROXYUSER
    # SESSION_USER: MYSESSIONUSER

Pooled connection examples:

    # Basic Authentication without a proxy
    pool = oracledb.create_pool(user="myproxyuser", password="myproxyuserpw",
                                dsn="dbhost.example.com/orclpdb")
    connection = pool.acquire()
    # PROXY_USER:   None
    # SESSION_USER: MYPROXYUSER

    # Basic Authentication with proxy
    pool = oracledb.create_pool(user="myproxyuser[mysessionuser]", password="myproxyuserpw",
                                dsn="dbhost.example.com/orclpdb",
                                homogeneous=False)

    connection = pool.acquire()
    # PROXY_USER:   MYPROXYUSER
    # SESSION_USER: MYSESSIONUSER

Note the use of a heterogeneous pool in the example above. This is required in this scenario.

## 4.7. Connecting Using External Authentication

Instead of storing the database username and password in Python scripts or environment variables, database access can be authenticated by an outside system. External Authentication allows applications to validate user access by an external password store (such as an Oracle Wallet), by the operating system, or with an external authentication service.

Note

Connecting to Oracle Database using external authentication is only supported in the python-oracledb Thick mode. See Enabling python-oracledb Thick mode.

### 4.7.1. Using an Oracle Wallet for External Authentication

The following steps give an overview of using an Oracle Wallet. Wallets should be kept securely. Wallets can be managed with Oracle Wallet Manager.

In this example the wallet is created for the `myuser` schema in the directory `/home/oracle/wallet_dir`. The `mkstore` command is available from a full Oracle client or Oracle Database installation. If you have been given wallet by your DBA, skip to step 3.

1. First create a new wallet as the `oracle` user:

       mkstore -wrl "/home/oracle/wallet_dir" -create

   This will prompt for a new password for the wallet.

2. Create the entry for the database user name and password that are currently hardcoded in your Python scripts. Use either of the methods shown below. They will prompt for the wallet password that was set in the first step.

   Method 1 - Using an Easy Connect string:

       mkstore -wrl "/home/oracle/wallet_dir" -createCredential dbhost.example.com/orclpdb myuser myuserpw

   Method 2 - Using a connect name identifier:

       mkstore -wrl "/home/oracle/wallet_dir" -createCredential mynetalias myuser myuserpw

   The alias key `mynetalias` immediately following the `-createCredential` option will be the connect name to be used in Python scripts. If your application connects with multiple different database users, you could create a wallet entry with different connect names for each.

   You can see the newly created credential with:

       mkstore -wrl "/home/oracle/wallet_dir" -listCredential

3. Skip this step if the wallet was created using an Easy Connect String. Otherwise, add an entry in tnsnames.ora for the connect name as follows:

       mynetalias =
           (DESCRIPTION =
               (ADDRESS = (PROTOCOL = TCP)(HOST = dbhost.example.com)(PORT = 1521))
               (CONNECT_DATA =
                   (SERVER = DEDICATED)
                   (SERVICE_NAME = orclpdb)
               )
           )

   The file uses the description for your existing database and sets the connect name alias to `mynetalias`, which is the identifier used when adding the wallet entry.

4. Add the following wallet location entry in the sqlnet.ora file, using the `DIRECTORY` you created the wallet in:

       WALLET_LOCATION =
           (SOURCE =
               (METHOD = FILE)
               (METHOD_DATA =
                   (DIRECTORY = /home/oracle/wallet_dir)
               )
           )
       SQLNET.WALLET_OVERRIDE = TRUE

   Examine the Oracle documentation for full settings and values.

5. Ensure the configuration files are in a default location or TNS_ADMIN is set to the directory containing them. See Optional Oracle Net Configuration Files.

With an Oracle wallet configured, and readable by you, your scripts can connect using:

    connection = oracledb.connect(externalauth=True, dsn="mynetalias")

or:

    pool = oracledb.create_pool(externalauth=True, homogeneous=False,
                                dsn="mynetalias")
    pool.acquire()

The `dsn` must match the one used in the wallet.

After connecting, the query:

    SELECT SYS_CONTEXT('USERENV', 'SESSION_USER') FROM DUAL;

will show:

    MYUSER

Note

Wallets are also used to configure Transport Layer Security (TLS) connections. If you are using a wallet like this, you may need a database username and password in `oracledb.connect()` and `oracledb.create_pool()` calls.

External Authentication and Proxy Authentication

The following examples show external wallet authentication combined with proxy authentication. These examples use the wallet configuration from above, with the addition of a grant to another user:

    ALTER USER mysessionuser GRANT CONNECT THROUGH myuser;

After connection, you can check who the session user is with:

    SELECT SYS_CONTEXT('USERENV', 'PROXY_USER'),
           SYS_CONTEXT('USERENV', 'SESSION_USER')
    FROM DUAL;

Standalone connection example:

    # External Authentication with proxy
    connection = oracledb.connect(user="[mysessionuser]", dsn="mynetalias")
    # PROXY_USER:   MYUSER
    # SESSION_USER: MYSESSIONUSER

You can also explicitly set the `externalauth` parameter to True in standalone connections as shown below. The `externalauth` parameter is optional.

    # External Authentication with proxy when externalauth is set to True
    connection = oracledb.connect(user="[mysessionuser]", dsn="mynetalias",
                                  externalauth=True)
    # PROXY_USER:   MYUSER
    # SESSION_USER: MYSESSIONUSER

Pooled connection example:

    # External Authentication with proxy
    pool = oracledb.create_pool(externalauth=True, homogeneous=False,
                                dsn="mynetalias")
    pool.acquire(user="[mysessionuser]")
    # PROXY_USER:   MYUSER
    # SESSION_USER: MYSESSIONUSER

The following usage is not supported:

    pool = oracledb.create_pool(user="[mysessionuser]", externalauth=True,
                                homogeneous=False, dsn="mynetalias")
    pool.acquire()

### 4.7.2. Operating System Authentication

With Operating System authentication, Oracle allows user authentication to be performed by the operating system. The following steps give an overview of how to implement OS Authentication on Linux.

1. Log in to your computer. The commands used in these steps assume the operating system user name is “oracle”.

2. Log in to SQL*Plus as the SYSTEM user and verify the value for the `OS_AUTHENT_PREFIX` parameter:

       SQL> SHOW PARAMETER os_authent_prefix

       NAME                                 TYPE        VALUE
       ------------------------------------ ----------- ------------------------------
       os_authent_prefix                    string      ops$

3. Create an Oracle database user using the `os_authent_prefix` determined in step 2, and the operating system user name:

>     CREATE USER ops$oracle IDENTIFIED EXTERNALLY;
>     GRANT CONNECT, RESOURCE TO ops$oracle;

In Python, connect using the following code:

    connection = oracledb.connect(dsn="mynetalias")

Your session user will be `OPS$ORACLE`.

If your database is not on the same computer as Python, you can perform testing by setting the database configuration parameter `remote_os_authent=true`. Beware of security concerns because this is insecure.

See Oracle Database Security Guide for more information about Operating System Authentication.

## 4.8. Token-Based Authentication

Token-Based Authentication allows users to connect to a database by using an encrypted authentication token without having to enter a database username and password. The authentication token must be valid and not expired for the connection to be successful. Users already connected will be able to continue work after their token has expired but they will not be able to reconnect without getting a new token.

The two authentication methods supported by python-oracledb are Open Authorization (OAuth 2.0) and Oracle Cloud Infrastructure (OCI) Identity and Access Management (IAM).

### 4.8.1. Connecting Using OAuth 2.0 Token-Based Authentication

Oracle Cloud Infrastructure (OCI) users can be centrally managed in a Microsoft Azure Active Directory (Azure AD) service. Open Authorization (OAuth 2.0) token-based authentication allows users to authenticate to Oracle Database using Azure AD OAuth2 tokens. Currently, only Azure AD tokens are supported. Ensure that you have a Microsoft Azure account and your Oracle Database is registered with Azure AD. See Configuring the Oracle Autonomous Database for Microsoft Azure AD Integration for more information. Both Thin and Thick modes of the python-oracledb driver support OAuth 2.0 token-based authentication.

When using python-oracledb in Thick mode, Oracle Client libraries 19.15 (or later), or 21.7 (or later) are needed.

OAuth 2.0 token-based authentication can be used for both standalone connections and connection pools. Tokens can be specified using the connection parameter introduced in python-oracledb 1.1. Users of earlier python-oracledb versions can alternatively use OAuth 2.0 Token-Based Authentication Connection Strings.

#### 4.8.1.1. OAuth2 Token Generation And Extraction

There are different ways to retrieve Azure AD OAuth2 tokens. Some of the ways to retrieve the OAuth2 tokens are detailed in Examples of Retrieving Azure AD OAuth2 Tokens. You can also retrieve Azure AD OAuth2 tokens by using Azure Identity client library for Python.

##### 4.8.1.1.1. Example of Using a TokenHandlerOAuth Class

Here, as an example, we are using a Python script to automate the process of generating and reading the Azure AD OAuth2 tokens.

    import json
    import os

    import oracledb
    import requests

    class TokenHandlerOAuth:

        def __init__(self,
                     file_name="cached_token_file_name",
                     api_key="api_key",
                     client_id="client_id",
                     client_secret="client_secret"):
            self.token = None
            self.file_name = file_name
            self.url = \
                f"https://login.microsoftonline.com/{api_key}/oauth2/v2.0/token"
            self.scope = \
                f"https://oracledevelopment.onmicrosoft.com/{client_id}/.default"
            if os.path.exists(file_name):
                with open(file_name) as f:
                    self.token = f.read().strip()
            self.api_key = api_key
            self.client_id = client_id
            self.client_secret = client_secret

        def __call__(self, refresh):
            if self.token is None or refresh:
                post_data = dict(client_id=self.client_id,
                                 grant_type="client_credentials",
                                 scope=self.scope,
                                 client_secret=self.client_secret)
                r = requests.post(url=self.url, data=post_data)
                result = json.loads(r.text)
                self.token = result["access_token"]
                with open(self.file_name, "w") as f:
                    f.write(self.token)
            return self.token

The TokenHandlerOAuth class uses a callable to generate and read the OAuth2 tokens. When the callable in the TokenHandlerAuth class is invoked for the first time to create a standalone connection or pool, the `refresh` parameter is False which allows the callable to return a cached token, if desired. The expiry date is then extracted from this token and compared with the current date. If the token has not expired, then it will be used directly. If the token has expired, the callable is invoked the second time with the `refresh` parameter set to True.

See Example of Using a Curl Command for an alternative way to generate the tokens.

#### 4.8.1.2. Standalone Connection Creation with OAuth2 Access Tokens

For OAuth 2.0 Token-Based Authentication, the `access_token` connection parameter must be specified. This parameter should be a string (or a callable that returns a string) specifying an Azure AD OAuth2 token.

Standalone connections can be created in the python-oracledb Thick and Thin modes using OAuth 2.0 token-based authentication. In the examples below, the `access_token` parameter is set to a callable.

In python-oracledb Thin mode

When connecting to Oracle Cloud Database with mutual TLS (mTLS) using OAuth2 tokens in the python-oracledb Thin mode, you need to explicitly set the `config_dir`, `wallet_location`, and `wallet_password` parameters of `connect()`. See, Connecting to Oracle Cloud Autonomous Databases. The following example shows a standalone connection creation using OAuth 2.0 token based authentication in the python-oracledb Thin mode. For information on TokenHandlerOAuth() used in the example, see Example of Using a TokenHandlerOAuth Class.

    connection = oracledb.connect(access_token=TokenHandlerOAuth(),
                                  dsn=mydb_low,
                                  config_dir="path_to_extracted_wallet_zip",
                                  wallet_location="location_of_pem_file",
                                  wallet_password=wp)

In python-oracledb Thick mode

In the python-oracledb Thick mode, you can create a standalone connection using OAuth2 tokens as shown in the example below. For information on TokenHandlerOAuth() used in the example, see Example of Using a TokenHandlerOAuth Class.

    connection = oracledb.connect(access_token=TokenHandlerOAuth(),
                                  externalauth=True,
                                  dsn=mydb_low)

#### 4.8.1.3. Connection Pool Creation with OAuth2 Access Tokens

For OAuth 2.0 Token-Based Authentication, the `access_token` connection parameter must be specified. This parameter should be a string (or a callable that returns a string) specifying an Azure AD OAuth2 token.

The `externalauth` parameter must be set to True in the python-oracledb Thick mode. The `homogeneous` parameter must be set to True in both the python-oracledb Thin and Thick modes.

Connection pools can be created in the python-oracledb Thick and Thin modes using OAuth 2.0 token-based authentication. In the examples below, the `access_token` parameter is set to a callable.

Note that the `access_token` parameter should be set to a callable. This is useful when the connection pool needs to expand and create new connections but the current token has expired. In such case, the callable should return a string specifying the new, valid Azure AD OAuth2 token.

In python-oracledb Thin mode

When connecting to Oracle Cloud Database with mutual TLS (mTLS) using OAuth2 tokens in the python-oracledb Thin mode, you need to explicitly set the `config_dir`, `wallet_location`, and `wallet_password` parameters of `create_pool()`. See, Connecting to Oracle Cloud Autonomous Databases. The following example shows a connection pool creation using OAuth 2.0 token based authentication in the python-oracledb Thin mode. For information on TokenHandlerOAuth() used in the example, see Example of Using a TokenHandlerOAuth Class.

    connection = oracledb.create_pool(access_token=TokenHandlerOAuth(),
                                      homogeneous=True, dsn=mydb_low,
                                      config_dir="path_to_extracted_wallet_zip",
                                      wallet_location="location_of_pem_file",
                                      wallet_password=wp
                                      min=1, max=5, increment=2)

In python-oracledb Thick mode

In the python-oracledb Thick mode, you can create a connection pool using OAuth2 tokens as shown in the example below. For information on TokenHandlerOAuth() used in the example, see Example of Using a TokenHandlerOAuth Class.

    pool = oracledb.create_pool(access_token=TokenHandlerOAuth(),
                                externalauth=True, homogeneous=True,
                                dsn=mydb_low, min=1, max=5, increment=2)

#### 4.8.1.4. OAuth 2.0 Token-Based Authentication Connection Strings

The connection string used by python-oracledb can specify the directory where the token file is located. This syntax is usable with older versions of python-oracledb. However, it is recommended to use connection parameters introduced in python-oracledb 1.1 instead. See OAuth 2.0 Token-Based Authentication.

Note

OAuth 2.0 Token-Based Authentication Connection Strings is only supported in the python-oracledb Thick mode. See Enabling python-oracledb Thick mode.

There are different ways to retrieve Azure AD OAuth2 tokens. Some of the ways to retrieve the OAuth2 tokens are detailed in Examples of Retrieving Azure AD OAuth2 Tokens. You can also retrieve Azure AD OAuth2 tokens by using Azure Identity client library for Python.

##### 4.8.1.4.1. Example of Using a Curl Command

Here, as an example, we are using Curl with a Resource Owner Password Credential (ROPC) Flow, that is, a `curl` command is used against the Azure AD API to get the Azure AD OAuth2 token:

    curl -X POST -H 'Content-Type: application/x-www-form-urlencoded'
    https://login.microsoftonline.com/your_tenant_id/oauth2/v2.0/token
    -d 'client_id=your_client_id'
    -d 'grant_type=client_credentials'
    -d 'scope=https://oracledevelopment.onmicrosoft.com/your_client_id/.default'
    -d 'client_secret=your_client_secret'

This command generates a JSON response with token type, expiration, and access token values. The JSON response needs to be parsed so that only the access token is written and stored in a file. You can save the value of `access_token` generated to a file and set `TOKEN_LOCATION` to the location of token file. See Example of Using a TokenHandlerOAuth Class for an example of using the TokenHandlerOAuth class to generate and read tokens.

The Oracle Net parameters `TOKEN_AUTH` and `TOKEN_LOCATION` must be set when you are using the connection string syntax. Also, the `PROTOCOL` parameter must be `tcps` and `SSL_SERVER_DN_MATCH` should be `ON`.

You can set `TOKEN_AUTH=OAUTH`. There is no default location set in this case, so you must set `TOKEN_LOCATION` to either of the following:

- A directory, in which case, you must create a file named `token` which contains the token value

- A fully qualified file name, in which case, you must specify the entire path of the file which contains the token value

You can either set `TOKEN_AUTH` and `TOKEN_LOCATION` in a sqlnet.ora file or alternatively, you can specify it inside a connect descriptor stored in tnsnames.ora file, for example:

    db_alias =
        (DESCRIPTION =
            (ADDRESS=(PROTOCOL=TCPS)(PORT=1522)(HOST=xxx.oraclecloud.com))
            (CONNECT_DATA=(SERVICE_NAME=xxx.adb.oraclecloud.com))
            (SECURITY =
                (SSL_SERVER_CERT_DN="CN=xxx.oraclecloud.com,OU=Oracle BMCS US, \
                 O=Oracle Corporation,L=Redwood City,ST=California,C=US")
                (TOKEN_AUTH=OAUTH)
                (TOKEN_LOCATION="/home/user1/mytokens/oauthtoken")
            )
        )

The `TOKEN_AUTH` and `TOKEN_LOCATION` values in a connection string take precedence over the `sqlnet.ora` settings.

Standalone connection example:

    connection = oracledb.connect(dsn=db_alias, externalauth=True)

Connection pool example:

    pool = oracledb.create_pool(dsn=db_alias, externalauth=True,
                                homogeneous=False, min=1, max=2, increment=1)

    connection = pool.acquire()

### 4.8.2. Connecting Using OCI IAM Token-Based Authentication

Oracle Cloud Infrastructure (OCI) Identity and Access Management (IAM) provides its users with a centralized database authentication and authorization system. Using this authentication method, users can use the database access token issued by OCI IAM to authenticate to the Oracle Cloud Database. Both Thin and Thick modes of the python-oracledb driver support OCI IAM token-based authentication.

When using python-oracledb in Thick mode, Oracle Client libraries 19.14 (or later), or 21.5 (or later) are needed.

OCI IAM token-based authentication can be used for both standalone connections and connection pools. Tokens can be specified using the connection parameter introduced in python-oracledb 1.1. Users of earlier python-oracledb versions can alternatively use OCI IAM Token-Based Authentication Connection Strings.

#### 4.8.2.1. OCI IAM Token Generation and Extraction

Authentication tokens can be generated through execution of an Oracle Cloud Infrastructure command line interface (OCI-CLI) command

    oci iam db-token get

On Linux, a folder `.oci/db-token` will be created in your home directory. It will contain the token and private key files needed by python-oracledb.

##### 4.8.2.1.1. Example of Using a TokenHandlerIAM Class

Here, as an example, we are using a Python script to automate the process of generating and reading the OCI IAM tokens.

    import os

    import oracledb

    class TokenHandlerIAM:

        def __init__(self,
                     dir_name="dir_name",
                     command="oci iam db-token get"):
            self.dir_name = dir_name
            self.command = command
            self.token = None
            self.private_key = None

        def __call__(self, refresh):
            if refresh:
                if os.system(self.command) != 0:
                    raise Exception("token command failed!")
            if self.token is None or refresh:
                self.read_token_info()
            return (self.token, self.private_key)

        def read_token_info(self):
            token_file_name = os.path.join(self.dir_name, "token")
            pkey_file_name = os.path.join(self.dir_name, "oci_db_key.pem")
            with open(token_file_name) as f:
                self.token = f.read().strip()
            with open(pkey_file_name) as f:
                if oracledb.is_thin_mode():
                    self.private_key = f.read().strip()
                else:
                    lines = [s for s in f.read().strip().split("\n")
                             if s not in ('-----BEGIN PRIVATE KEY-----',
                                          '-----END PRIVATE KEY-----')]
                    self.private_key = "".join(lines)

The TokenHandlerIAM class uses a callable to generate and read the OCI IAM tokens. When the callable in the TokenHandlerIAM class is invoked for the first time to create a standalone connection or pool, the `refresh` parameter is False which allows the callable to return a cached token, if desired. The expiry date is then extracted from this token and compared with the current date. If the token has not expired, then it will be used directly. If the token has expired, the callable is invoked the second time with the `refresh` parameter set to True.

#### 4.8.2.2. Standalone Connection Creation with OCI IAM Access Tokens

For OCI IAM Token-Based Authentication, the `access_token` connection parameter must be specified. This parameter should be a 2-tuple (or a callable that returns a 2-tuple) containing the token and private key.

Standalone connections can be created in the python-oracledb Thick and Thin modes using OCI IAM token-based authentication. In the examples below, the `access_token` parameter is set to a callable.

In python-oracledb Thin mode

When connecting to Oracle Cloud Database with mutual TLS (mTLS) using OCI IAM tokens in the python-oracledb Thin mode, you need to explicitly set the `config_dir`, `wallet_location`, and `wallet_password` parameters of `connect()`. See, Connecting to Oracle Cloud Autonomous Databases. The following example shows a standalone connection creation using OCI IAM token based authentication in the python-oracledb Thin mode. For information on TokenHandlerIAM() used in the example, see Example of Using a TokenHandlerIAM Class.

    connection = oracledb.connect(access_token=TokenHandlerIAM(),
                                  dsn=mydb_low,
                                  config_dir="path_to_extracted_wallet_zip",
                                  wallet_location="location_of_pem_file",
                                  wallet_password=wp)

In python-oracledb Thick mode

In the python-oracledb Thick mode, you can create a standalone connection using OCI IAM tokens as shown in the example below. For information on TokenHandlerIAM() used in the example, see Example of Using a TokenHandlerIAM Class.

    connection = oracledb.connect(access_token=TokenHandlerIAM(),
                                  externalauth=True,
                                  dsn=mydb_low)

#### 4.8.2.3. Connection Pool Creation with OCI IAM Access Tokens

For OCI IAM Token-Based Authentication, the `access_token` connection parameter must be specified. This parameter should be a 2-tuple (or a callable that returns a 2-tuple) containing the token and private key.

The `externalauth` parameter must be set to True in the python-oracledb Thick mode. The `homogeneous` parameter must be set to True in both the python-oracledb Thin and Thick modes.

Connection pools can be created in the python-oracledb Thick and Thin modes using OCI IAM token-based authentication. In the examples below, the `access_token` parameter is set to a callable.

Note that the `access_token` parameter should be set to a callable. This is useful when the connection pool needs to expand and create new connections but the current token has expired. In such case, the callable should return a 2-tuple (token, private key) specifying the new, valid access token.

In python-oracledb Thin mode

When connecting to Oracle Cloud Database with mutual TLS (mTLS) using OCI IAM tokens in the python-oracledb Thin mode, you need to explicitly set the `config_dir`, `wallet_location`, and `wallet_password` parameters of `create_pool()`. See, Connecting to Oracle Cloud Autonomous Databases. The following example shows a connection pool creation using OCI IAM token based authentication in the python-oracledb Thin mode. For information on TokenHandlerIAM() used in the example, see Example of Using a TokenHandlerIAM Class.

    connection = oracledb.connect(access_token=TokenHandlerIAM(),
                                  homogeneous=True, dsn=mydb_low,
                                  config_dir="path_to_extracted_wallet_zip",
                                  wallet_location="location_of_pem_file",
                                  wallet_password=wp
                                  min=1, max=5, increment=2)

In python-oracledb Thick mode

In the python-oracledb Thick mode, you can create a connection pool using OCI IAM tokens as shown in the example below. For information on TokenHandlerIAM() used in the example, see Example of Using a TokenHandlerIAM Class.

    pool = oracledb.create_pool(access_token=TokenHandlerIAM(),
                                externalauth=True,
                                homogeneous=True,
                                dsn=mydb_low,
                                min=1, max=5, increment=2)

#### 4.8.2.4. OCI IAM Token-Based Authentication Connection Strings

The connection string used by python-oracledb can specify the directory where the token and private key files are located. This syntax is usable with older versions of python-oracledb. However, it is recommended to use connection parameters introduced in python-oracledb 1.1 instead. See OCI IAM Token-Based Authentication.

Note

OCI IAM Token-Based Authentication Connection Strings is only supported in the python-oracledb Thick mode. See Enabling python-oracledb Thick mode.

The Oracle Cloud Infrastructure command line interface (OCI-CLI) can be used externally to get tokens and private keys from OCI IAM, for example with the OCI-CLI `oci iam db-token get` command.

The Oracle Net parameter `TOKEN_AUTH` must be set when you are using the connection string syntax. Also, the `PROTOCOL` parameter must be `tcps` and `SSL_SERVER_DN_MATCH` should be `ON`.

You can set `TOKEN_AUTH=OCI_TOKEN` in a `sqlnet.ora` file. Alternatively, you can specify it in a connect descriptor, for example:

    db_alias =
        (DESCRIPTION =
            (ADDRESS=(PROTOCOL=TCPS)(PORT=1522)(HOST=xxx.oraclecloud.com))
            (CONNECT_DATA=(SERVICE_NAME=xxx.adb.oraclecloud.com))
            (SECURITY =
                (SSL_SERVER_CERT_DN="CN=xxx.oraclecloud.com,OU=Oracle BMCS US, \
                 O=Oracle Corporation,L=Redwood City,ST=California,C=US")
                (TOKEN_AUTH=OCI_TOKEN)
            )
        )

The default location for the token and private key is the same default location that the OCI-CLI tool writes to. For example `~/.oci/db-token/` on Linux.

If the token and private key files are not in the default location then their directory must be specified with the `TOKEN_LOCATION` parameter in a sqlnet.ora file or in a connect descriptor stored inside tnsnames.ora file, for example:

    db_alias =
        (DESCRIPTION =
            (ADDRESS=(PROTOCOL=TCPS)(PORT=1522)(HOST=xxx.oraclecloud.com))
            (CONNECT_DATA=(SERVICE_NAME=xxx.adb.oraclecloud.com))
            (SECURITY =
                (SSL_SERVER_CERT_DN="CN=xxx.oraclecloud.com,OU=Oracle BMCS US, \
                 O=Oracle Corporation,L=Redwood City,ST=California,C=US")
                (TOKEN_AUTH=OCI_TOKEN)
                (TOKEN_LOCATION="/path/to/token/folder")
            )
        )

The `TOKEN_AUTH` and `TOKEN_LOCATION` values in a connection string take precedence over the `sqlnet.ora` settings.

Standalone connection example:

    connection = oracledb.connect(dsn=db_alias, externalauth=True)

Connection pool example:

    pool = oracledb.create_pool(dsn=db_alias, externalauth=True,
                                homogeneous=False, min=1, max=2, increment=1)

    connection = pool.acquire()

## 4.9. Privileged Connections

The `mode` parameter of the function `oracledb.connect()` specifies the database privilege that you want to associate with the user.

The example below shows how to connect to Oracle Database as SYSDBA:

    connection = oracledb.connect(user="sys", password=syspwd,
                                  dsn="dbhost.example.com/orclpdb",
                                  mode=oracledb.AUTH_MODE_SYSDBA)

    with connection.cursor() as cursor:
        cursor.execute("GRANT SYSOPER TO hr")

This is equivalent to executing the following in SQL*Plus:

    CONNECT sys/syspwd AS SYSDBA
    GRANT SYSOPER TO hr;

## 4.10. Securely Encrypting Network Traffic to Oracle Database

You can encrypt data transferred between the Oracle Database and python-oracledb so that unauthorized parties are not able to view plain text values as the data passes over the network.

Both python-oracledb Thin and Thick modes support TLS. Refer to the Oracle Database Security Guide for more configuration information.

### 4.10.1. Native Network Encryption

The python-oracledb Thick mode can additionally use Oracle Database’s native network encryption.

With native network encryption, the client and database server negotiate a key using Diffie-Hellman key exchange. This provides protection against man-in-the-middle attacks.

Native network encryption can be configured by editing Oracle Net’s optional sqlnet.ora configuration file. The file on either the database server and/or on each python-oracledb ‘client’ machine can be configured. Parameters control whether data integrity checking and encryption is required or just allowed, and which algorithms the client and server should consider for use.

As an example, to ensure all connections to the database are checked for integrity and are also encrypted, create or edit the Oracle Database `$ORACLE_HOME/network/admin/sqlnet.ora` file. Set the checksum negotiation to always validate a checksum and set the checksum type to your desired value. The network encryption settings can similarly be set. For example, to use the SHA512 checksum and AES256 encryption use:

    SQLNET.CRYPTO_CHECKSUM_SERVER = required
    SQLNET.CRYPTO_CHECKSUM_TYPES_SERVER = (SHA512)
    SQLNET.ENCRYPTION_SERVER = required
    SQLNET.ENCRYPTION_TYPES_SERVER = (AES256)

If you definitely know that the database server enforces integrity and encryption, then you do not need to configure python-oracledb separately. However, you can also, or alternatively do so, depending on your business needs. Create a `sqlnet.ora` on your client machine and locate it with other Optional Oracle Net Configuration Files:

    SQLNET.CRYPTO_CHECKSUM_CLIENT = required
    SQLNET.CRYPTO_CHECKSUM_TYPES_CLIENT = (SHA512)
    SQLNET.ENCRYPTION_CLIENT = required
    SQLNET.ENCRYPTION_TYPES_CLIENT = (AES256)

The client and server sides can negotiate the protocols used if the settings indicate more than one value is accepted.

Note that these are example settings only. You must review your security requirements and read the documentation for your Oracle version. In particular, review the available algorithms for security and performance.

The `NETWORK_SERVICE_BANNER` column of the database view V$SESSION_CONNECT_INFO can be used to verify the encryption status of a connection.

## 4.11. Resetting Passwords

After connecting to Oracle Database, passwords can be changed by calling `Connection.changepassword()`:

    # Get the passwords from somewhere, such as prompting the user
    oldpwd = getpass.getpass(f"Old Password for {username}: ")
    newpwd = getpass.getpass(f"New Password for {username}: ")

    connection.changepassword(oldpwd, newpwd)

When a password has expired and you cannot connect directly, you can connect and change the password in one operation by using the `newpassword` parameter of the function `oracledb.connect()` constructor:

    # Get the passwords from somewhere, such as prompting the user
    oldpwd = getpass.getpass(f"Old Password for {username}: ")
    newpwd = getpass.getpass(f"New Password for {username}: ")

    connection = oracledb.connect(user=username, password=oldpwd,
                                  dsn="dbhost.example.com/orclpdb",
                                  newpassword=newpwd)

## 4.12. Connecting to Oracle Cloud Autonomous Databases

Python applications can connect to Oracle Autonomous Database (ADB) in Oracle Cloud using one-way TLS (Transport Layer Security) or mutual TLS (mTLS). One-way TLS and mTLS provide enhanced security for authentication and encryption.

A database username and password are still required for your application connections. If you need to create a new database schema so you do not login as the privileged ADMIN user, refer to the relevant Oracle Cloud documentation, for example see Create Database Users in the Oracle Autonomous Database manual.

### 4.12.1. One-way TLS Connection to Oracle Autonomous Database

With one-way TLS, python-oracledb applications can connect to Oracle ADB without using a wallet. Both Thin and Thick modes of the python-oracledb driver support one-way TLS. Applications that use the python-oracledb Thick mode, can connect to the Oracle ADB through one-way TLS only when using Oracle Client library versions 19.14 (or later) or 21.5 (or later).

To enable one-way TLS for an ADB instance, complete the following steps in an Oracle Cloud console in the Autonomous Database Information section of the ADB instance details:

1. Click the Edit link next to Access Control List to update the Access Control List (ACL). The Edit Access Control List dialog box is displayed.

2. In the Edit Access Control List dialog box, select the type of address list entries and the corresponding values. You can include the required IP addresses, hostnames, or Virtual Cloud Networks (VCNs). The ACL limits access to only the IP addresses or VCNs that have been defined and blocks all other incoming traffic.

3. Navigate back to the ADB instance details page and click the Edit link next to Mutual TLS (mTLS) Authentication. The Edit Mutual TLS Authentication is displayed.

4. In the Edit Mutual TLS Authentication dialog box, deselect the Require mutual TLS (mTLS) authentication check box to disable the mTLS requirement on Oracle ADB and click Save Changes.

5. Navigate back to the ADB instance details page and click DB Connection on the top of the page. A Database Connection dialog box is displayed.

6. In the Database Connection dialog box, select TLS from the Connection Strings drop-down list.

7. Copy the appropriate Connection String of the database instance used by your application.

Applications can connect to your Oracle ADB instance using the database credentials and the copied connect descriptor. For example, to connect as the ADMIN user:

    cs = '''(description = (retry_count=20)(retry_delay=3)(address=(protocol=tcps)
               (port=1522)(host=xxx.oraclecloud.com))(connect_data=(service_name=xxx.adb.oraclecloud.com))
               (security=(ssl_server_dn_match=yes)(ssl_server_cert_dn="CN=xxx.oraclecloud.com,OU=Oracle BMCS US,
               O=Oracle Corporation, L=Redwood City, T=California, C=US")))'''

    connection = oracledb.connect(user="admin", password=pw, dsn=cs)

You can download the ADB connection wallet using the DB Connection button and extract the `tnsnames.ora` file, or create one yourself if you prefer to keep connections strings out of application code, see Net Service Names for Connection Strings.

You may be interested in the blog post Easy wallet-less connections to Oracle Autonomous Databases in Python.

### 4.12.2. Mutual TLS (mTLS) Connection to Oracle Autonomous Database

To enable python-oracledb connections to Oracle Autonomous Database in Oracle Cloud using mTLS, a wallet needs to be downloaded from the cloud console. mTLS is sometimes called Two-way TLS.

#### 4.12.2.1. Install the Wallet and Network Configuration Files

From the Oracle Cloud console for the database, download the wallet zip file using the DB Connection button. The zip contains the wallet and network configuration files. When downloading the zip, the cloud console will ask you to create a wallet password. This password is used by python-oracledb in Thin mode, but not in Thick mode.

Note: keep wallet files in a secure location and only share them and the password with authorized users.

In python-oracledb Thin mode

For python-oracledb in Thin mode, only two files from the zip are needed:

- `tnsnames.ora` - Maps net service names used for application connection strings to your database services

- `ewallet.pem` - Enables SSL/TLS connections in Thin mode. Keep this file secure

If you do not have a PEM file, see Creating a PEM File for python-oracledb Thin Mode.

Unzip the wallet zip file and move the required files to a location such as `/opt/OracleCloud/MYDB`.

Connection can be made using your database credentials and setting the `dsn` parameter to the desired network alias from the `tnsnames.ora` file. The `config_dir` parameter indicates the directory containing `tnsnames.ora`. The `wallet_location` parameter is the directory containing the PEM file. In this example the files are in the same directory. The `wallet_password` parameter should be set to the password created in the cloud console when downloading the wallet. For example, to connect as the ADMIN user using the `mydb_low` network service name:

    connection = oracledb.connect(user="admin", password=pw, dsn="mydb_low",
                                  config_dir="/opt/OracleCloud/MYDB",
                                  wallet_location="/opt/OracleCloud/MYDB",
                                  wallet_password=wp)

In python-oracledb Thick mode

For python-oracledb in Thick mode, only these files from the zip are needed:

- `tnsnames.ora` - Maps net service names used for application connection strings to your database services

- `sqlnet.ora` - Configures Oracle Network settings

- `cwallet.sso` - Enables SSL/TLS connections in Thick mode. Keep this file secure

Unzip the wallet zip file. There are two options for placing the required files:

- Move the three files to the `network/admin` directory of the client libraries used by your application. For example if you are using Instant Client 19c and it is in `$HOME/instantclient_19_15`, then you would put the wallet files in `$HOME/instantclient_19_15/network/admin/`.

  Connection can be made using your database credentials and setting the `dsn` parameter to the desired network alias from the `tnsnames.ora` file. For example, to connect as the ADMIN user using the `mydb_low` network service name:

      connection = oracledb.connect(user="admin", password=pw, dsn="mydb_low")

- Alternatively, move the three files to any accessible directory, for example `/opt/OracleCloud/MYDB`.

  Then edit `sqlnet.ora` and change the wallet location directory to the directory containing the `cwallet.sso` file. For example:

      WALLET_LOCATION = (SOURCE = (METHOD = file) (METHOD_DATA = (DIRECTORY="/opt/OracleCloud/MYDB")))
      SSL_SERVER_DN_MATCH=yes

  Since the `tnsnames.ora` and `sqlnet.ora` files are not in the default location, your application needs to indicate where they are, either with the `config_dir` parameter to `oracledb.init_oracle_client()`, or using the `TNS_ADMIN` environment variable. See Optional Oracle Net Configuration Files. (Neither of these settings are needed, and you do not need to edit `sqlnet.ora`, if you have put all the files in the `network/admin` directory.)

  For example, to connect as the ADMIN user using the `mydb_low` network service name:

      oracledb.init_oracle_client(config_dir="/opt/OracleCloud/MYDB")

      connection = oracledb.connect(user="admin", password=pw, dsn="mydb_low")

In python-oracle Thick mode, to create mTLS connections in one Python process to two or more Oracle Autonomous Databases, move each `cwallet.sso` file to its own directory. For each connection use different connection string `WALLET_LOCATION` parameters to specify the directory of each `cwallet.sso` file. It is recommended to use Oracle Client libraries 19.17 (or later) when using multiple wallets.

#### 4.12.2.2. Access Through a Proxy

If you are behind a firewall, you can tunnel TLS/SSL connections via a proxy using HTTPS_PROXY in the connect descriptor or setting connection attributes. Successful connection depends on specific proxy configurations. Oracle does not recommend doing this when performance is critical.

In python-oracledb Thin mode

The proxy settings can be passed during connection creation:

    connection = oracledb.connect(user="admin", password=pw, dsn="mydb_low",
                                  config_dir="/opt/OracleCloud/MYDB",
                                  wallet_location="/opt/OracleCloud/MYDB", wallet_password=wp,
                                  https_proxy='myproxy.example.com', https_proxy_port=80)

Alternatively, edit `tnsnames.ora` and add an `HTTPS_PROXY` proxy name and `HTTPS_PROXY_PORT` port to the connect descriptor address list of any service name you plan to use, for example:

    mydb_low = (description=
        (address=
        (https_proxy=myproxy.example.com)(https_proxy_port=80)
        (protocol=tcps)(port=1522)(host= . . . )

    connection = oracledb.connect(user="admin", password=pw, dsn="mydb_low",
                                  config_dir="/opt/OracleCloud/MYDB",
                                  wallet_location="/opt/OracleCloud/MYDB", wallet_password=wp)

In python-oracledb Thick mode

Edit `sqlnet.ora` and add a line:

    SQLNET.USE_HTTPS_PROXY=on

Edit `tnsnames.ora` and add an `HTTPS_PROXY` proxy name and `HTTPS_PROXY_PORT` port to the connect descriptor address list of any service name you plan to use, for example:

    mydb_high = (description=
        (address=
        (https_proxy=myproxy.example.com)(https_proxy_port=80)
        (protocol=tcps)(port=1522)(host= . . . )

#### 4.12.2.3. Using the Easy Connect Syntax with Autonomous Database

When python-oracledb is using Oracle Client libraries 19c or later, you can optionally use the Easy Connect syntax to connect to Oracle Autonomous Database.

The mapping from the cloud `tnsnames.ora` entries to an Easy Connect Plus string is:

    protocol://host:port/service_name?wallet_location=/my/dir&retry_count=N&retry_delay=N

For example, if your `tnsnames.ora` file had an entry:

    cjjson_high = (description=(retry_count=20)(retry_delay=3)
        (address=(protocol=tcps)(port=1522)
        (host=adb.ap-sydney-1.oraclecloud.com))
        (connect_data=(service_name=abc_cjjson_high.adb.oraclecloud.com))
        (security=(ssl_server_cert_dn="CN=adb.ap-sydney-1.oraclecloud.com,OU=Oracle ADB SYDNEY,O=Oracle Corporation,L=Redwood City,ST=California,C=US")))

Then your applications can connect using the connection string:

    dsn = "tcps://adb.ap-sydney-1.oraclecloud.com:1522/abc_cjjson_high.adb.oraclecloud.com?wallet_location=/Users/cjones/Cloud/CJJSON&retry_count=20&retry_delay=3"
    connection = oracledb.connect(user="hr", password=userpwd, dsn=dsn)

The `wallet_location` parameter needs to be set to the directory containing the `cwallet.sso` or `ewallet.pem` file from the wallet zip. The other wallet files, including `tnsnames.ora`, are not needed when you use the Easy Connect Plus syntax.

You can add other Easy Connect parameters to the connection string, for example:

    dsn = dsn + "&https_proxy=myproxy.example.com&https_proxy_port=80"

With python-oracledb Thin mode, the wallet password needs to be passed as a connection parameter.

#### 4.12.2.4. Creating a PEM File for python-oracledb Thin Mode

For mutual TLS in python-oracledb Thin mode, the certificate must be Privacy Enhanced Mail (PEM) format. If you are using Oracle Autonomous Database and your wallet zip file does not already include a PEM file, then you can convert the PKCS12 `ewallet.p12` file to PEM format using third party tools or the script below.

For example, invoke the conversion script by passing the wallet password and the directory containing the PKCS file:

    python create_pem.py --wallet-password 'xxxxx' /Users/scott/cloud_configs/MYDBDIR

Once the PEM file has been created, you can use it by passing its directory location as the `wallet_location` parameter to `oracledb.connect()` or `oracledb.create_pool()`. These methods also accept a `wallet_password` parameter. See Mutual TLS (mTLS) Connection to Oracle Autonomous Database.

Script to convert from PKCS12 to PEM

    # create_pem.py

    import argparse
    import getpass
    import os

    from cryptography.hazmat.primitives.serialization \
            import pkcs12, Encoding, PrivateFormat, BestAvailableEncryption, \
                   NoEncryption

    # parse command line
    parser = argparse.ArgumentParser(description="convert PKCS#12 to PEM")
    parser.add_argument("wallet_location",
                        help="the directory in which the PKCS#12 encoded "
                             "wallet file ewallet.p12 is found")
    parser.add_argument("--wallet-password",
                        help="the password for the wallet which is used to "
                             "decrypt the PKCS#12 encoded wallet file; if not "
                             "specified, it will be requested securely")
    parser.add_argument("--no-encrypt",
                        dest="encrypt", action="store_false", default=True,
                        help="do not encrypt the converted PEM file with the "
                             "wallet password")
    args = parser.parse_args()

    # validate arguments and acquire password if one was not specified
    pkcs12_file_name = os.path.join(args.wallet_location, "ewallet.p12")
    if not os.path.exists(pkcs12_file_name):
        msg = f"wallet location {args.wallet_location} does not contain " \
               "ewallet.p12"
        raise Exception(msg)
    if args.wallet_password is None:
        args.wallet_password = getpass.getpass()

    pem_file_name = os.path.join(args.wallet_location, "ewallet.pem")
    pkcs12_data = open(pkcs12_file_name, "rb").read()
    result = pkcs12.load_key_and_certificates(pkcs12_data,
                                              args.wallet_password.encode())
    private_key, certificate, additional_certificates = result
    if args.encrypt:
        encryptor = BestAvailableEncryption(args.wallet_password.encode())
    else:
        encryptor = NoEncryption()
    with open(pem_file_name, "wb") as f:
        f.write(private_key.private_bytes(Encoding.PEM, PrivateFormat.PKCS8,
                                          encryptor))
        f.write(certificate.public_bytes(Encoding.PEM))
        for cert in additional_certificates:
            f.write(cert.public_bytes(Encoding.PEM))
    print("PEM file", pem_file_name, "written.")

## 4.13. Connecting to Sharded Databases

Oracle Sharding can be used to horizontally partition data across independent databases. A database table can be split so each shard contains a table with the same columns but a different subset of rows. These tables are known as sharded tables. Sharding is configured in Oracle Database, see the Oracle Sharding manual. Sharding requires Oracle Database and Oracle Client libraries 12.2, or later.

Note

Sharding is only supported in the python-oracledb Thick mode. See Enabling python-oracledb Thick mode.

The `oracledb.connect()` and `ConnectionPool.acquire()` functions accept `shardingkey` and `supershardingkey` parameters that are a sequence of values used to route the connection directly to a given shard. A sharding key is always required. A super sharding key is additionally required when using composite sharding, which is when data has been partitioned by a list or range (the super sharding key), and then further partitioned by a sharding key.

When creating a connection pool, the `oracledb.create_pool()` attribute `max_sessions_per_shard` can be set. This is used to balance connections in the pool equally across shards. It requires Oracle Client libraries 18.3 or later.

Shard key values may be of type string (mapping to VARCHAR2 shard keys), number (NUMBER), bytes (RAW), or date (DATE). Multiple types may be used in each array. Sharding keys of TIMESTAMP type are not supported.

When connected to a shard, queries will only return data from that shard. For queries that need to access data from multiple shards, connections can be established to the coordinator shard catalog database. In this case, no shard key or super shard key is used.

As an example of direct connection, if sharding had been configured on a single VARCHAR2 column like:

    CREATE SHARDED TABLE customers (
      cust_id NUMBER,
      cust_name VARCHAR2(30),
      class VARCHAR2(10) NOT NULL,
      signup_date DATE,
      cust_code RAW(20),
      CONSTRAINT cust_name_pk PRIMARY KEY(cust_name))
      PARTITION BY CONSISTENT HASH (cust_name)
      PARTITIONS AUTO TABLESPACE SET ts1;

then direct connection to a shard can be made by passing a single sharding key:

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="dbhost.example.com/orclpdb",
                                  shardingkey=["SCOTT"])

Numbers keys can be used in a similar way:

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="dbhost.example.com/orclpdb",
                                  shardingkey=[110])

When sharding by DATE, you can connect like:

    import datetime

    d = datetime.datetime(2014, 7, 3)

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="dbhost.example.com/orclpdb",
                                  shardingkey=[d])

When sharding by RAW, you can connect like:

    b = b'\x01\x04\x08';

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="dbhost.example.com/orclpdb",
                                  shardingkey=[b])

Multiple keys can be specified, for example:

    key_list = [70, "SCOTT", "gold", b'\x00\x01\x02']

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="dbhost.example.com/orclpdb",
                                  shardingkey=key_list)

A super sharding key example is:

    connection = oracledb.connect(user="hr", password=userpwd,
                                  dsn="dbhost.example.com/orclpdb",
                                  supershardingkey=["goldclass"],
                                  shardingkey=["SCOTT"])