Connecting to Oracle Database¶
Establishing Database Connections¶
There are two ways to connect to Oracle Database using cx_Oracle:
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
cx_Oracle.SessionPool()at application initialization time, and then
SessionPool.acquire()can be called to obtain a connection from a pool.
Many connection behaviors can be controlled by cx_Oracle options. Other settings can be configured in Optional Oracle Net Configuration Files or in Optional Oracle Client Configuration Files. These include limiting the amount of time that opening a connection can take, or enabling network encryption.
Example: Standalone Connection to Oracle Database
import cx_Oracle userpwd = ". . ." # Obtain password string from a user prompt or environment variable connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com/orclpdb1", encoding="UTF-8")
cx_Oracle also supports external authentication so passwords do not need to be in the application.
Connections should be released when they are no longer needed by calling
Connection.close(). Alternatively, you may prefer to let connections
be automatically cleaned up when references to them go out of scope. This lets
cx_Oracle close dependent resources in the correct order. One other approach is
the use of a “with” block, for example:
with cx_Oracle.connect(userName, password, "dbhost.example.com/orclpdb1", encoding="UTF-8") as connection: cursor = connection.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.
Prompt closing of connections is important when using connection pools so connections are available for reuse by other pool users.
The data source name parameter
cx_Oracle.SessionPool() is the Oracle Database connection string
identifying which database service to connect to. The
dsn string can be one
- 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.
Easy Connect Syntax for Connection Strings¶
An Easy Connect string is often the simplest connection string to use for the
data source name parameter
cx_Oracle.SessionPool(). This method does not need configuration files
For example, to connect to the Oracle Database service
orclpdb1 that is
running on the host
dbhost.example.com with the default Oracle
Database port 1521, use:
connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com/orclpdb1", encoding="UTF-8")
If the database is using a non-default port, it must be specified:
connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com:1984/orclpdb1", encoding="UTF-8")
The Easy Connect syntax supports Oracle Database service names. It cannot be used with the older System Identifiers (SID).
The Easy Connect syntax has been extended in recent versions of Oracle Database client since its introduction in 10g. 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.
If you are using Oracle Client 19c, 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 lets some network configuration options be set. This means that a sqlnet.ora file is not needed for some common connection scenarios.
Oracle Net Connect Descriptor Strings¶
cx_Oracle.makedsn() function can be used to construct a connect
descriptor string for the data source name parameter
makedsn() function accepts the database hostname, the port
number, and the service name. It also supports sharding
For example, to connect to the Oracle Database service
orclpdb1 that is
running on the host
dbhost.example.com with the default Oracle
Database port 1521, use:
dsn = cx_Oracle.makedsn("dbhost.example.com", 1521, service_name="orclpdb1") connection = cx_Oracle.connect("hr", userpwd, dsn, encoding="UTF-8")
Note the use of the named argument
service_name. By default, the third
makedsn() is a database System Identifier (SID),
not a service name. However, almost all current databases use service names.
The value of
dsn in this example is the connect descriptor string:
You can manually create similar connect descriptor strings. This lets you extend the syntax, for example to support failover. These strings can be embedded directly in the application:
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 = cx_Oracle.connect("hr", userpwd, dsn, encoding="UTF-8")
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
cx_Oracle.SessionPool(). For example,
tnsnames.ora file with the following contents:
ORCLPDB1 = (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = dbhost.example.com)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = orclpdb1) ) )
then you could connect using the following code:
connection = cx_Oracle.connect("hr", userpwd, "orclpdb1", encoding="UTF-8")
For more information about Net Service Names, see Database Net Services Reference.
JDBC and Oracle SQL Developer Connection Strings¶
The cx_Oracle connection string syntax is different to Java JDBC and the common Oracle SQL Developer syntax. If these JDBC connection strings reference a service name like:
then use Oracle’s Easy Connect syntax in cx_Oracle:
connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com:1521/orclpdb1", encoding="UTF-8")
Alternatively, if a JDBC connection string uses an old-style Oracle SID “system identifier”, and the database does not have a service name:
then a connect descriptor string from
makedsn() can be used in the
dsn = cx_Oracle.makedsn("dbhost.example.com", 1521, sid="orcl") connection = cx_Oracle.connect("hr", userpwd, dsn, encoding="UTF-8")
Alternatively, create a
tnsnames.ora (see Optional Oracle Net Configuration Files) entry, for
finance = (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = dbhost.example.com)(PORT = 1521)) (CONNECT_DATA = (SID = ORCL) ) )
This can be referenced in cx_Oracle:
connection = cx_Oracle.connect("hr", userpwd, "finance", encoding="UTF-8")
cx_Oracle’s connection pooling lets applications create and maintain a pool of connections to the database. Connection pooling is important for performance when applications frequently connect and disconnect from the database. The pool implementation uses Oracle’s session pool technology which supports Oracle’s high availability features and is recommended for applications that must be reliable. This also means that small pools can be useful for applications that want a few connections available for infrequent use.
A connection pool is created by calling
is generally called during application initialization. The initial pool size
and the maximum pool size are provided at the time of pool creation. When the
pool needs to grow, new connections are created automatically. The pool can
shrink back to the minimum size when connections are no longer in use. For
pools created with external authentication, with
homogeneous set to False, or when using Database Resident Connection Pooling (DRCP), then
the number of connections initially created is zero even if a larger value is
min. Also in these cases the pool increment is always 1,
regardless of the value of
After a pool has been created, connections can be obtained from it by calling
acquire(). These connections can be used in the same way
that standalone connections are used.
Connections acquired from the pool should be released back to the pool using
Connection.close() when they are no
longer required. Otherwise, they will be released back to the pool
automatically when all of the variables referencing the connection go out of
scope. This make connections available for other users of the pool.
The session pool can be completely closed using
The example below shows how to connect to Oracle Database using a connection pool:
# Create the session pool pool = cx_Oracle.SessionPool("hr", userpwd, "dbhost.example.com/orclpdb1", min=2, max=5, increment=1, encoding="UTF-8") # Acquire a connection from the pool connection = pool.acquire() # Use the pooled connection cursor = connection.cursor() for result in cursor.execute("select * from mytab"): print(result) # Release the connection to the pool pool.release(connection) # Close the pool pool.close()
cx_Oracle.SessionPool() options can be used at pool creation. For
getmode value can be set so that any
aquire() call will wait
for a connection to become available if all are currently in use, for example:
# Create the session pool pool = cx_Oracle.SessionPool("hr", userpwd, "dbhost.example.com/orclpdb1", min=2, max=5, increment=1, getmode=cx_Oracle.SPOOL_ATTRVAL_WAIT, encoding="UTF-8")
Applications that are using connections concurrently in multiple threads should
threaded parameter to True when creating a connection pool:
# Create the session pool pool = cx_Oracle.SessionPool("hr", userpwd, "dbhost.example.com/orclpdb1", min=2, max=5, increment=1, threaded=True, encoding="UTF-8")
See ConnectionPool.py for an example.
SessionPool.acquire() returns, cx_Oracle does a lightweight check
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 killed by the DBA, or reached a database resource
manager quota limit. To help in those cases,
will also do a full round-trip ping to the database when it
is about to return a connection that was unused in the pool for 60 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, it won’t catch every failure. Also network timeouts and
session kills may occur after
acquire() and before
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. Oracle’s
Application Continuity can do this automatically in
some cases. Note both the lightweight and full ping connection checks can mask
performance-impacting configuration issues, for example firewalls killing
connections, so monitor the connection rate in AWR
for an unexpected value. You can explicitly initiate a full ping to check
connection liveness with
Connection.ping() but overuse will impact
performance and scalability.
Connection Pool Sizing¶
The Oracle Real-World Performance Group’s recommendation is to use fixed size
connection pools. The values of
max should be the same (and the
increment equal to zero). This avoids connection storms 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
guarantee that the database can handle the upper pool size. For example, if a
pool needs to grow but the database resources are limited, then
SessionPool.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 size before users access the application. With a dynamically
growing pool, the error may occur much later after the pool has been in use for
The Real-World Performance Group also recommends keeping pool sizes small, as 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 cx_Oracle and the database.
Session CallBacks for Setting Pooled Connection State¶
Applications can set “session” state in each connection. Examples of session
state are NLS 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.
enables efficient setting of session state so that connections have a
known session state, without requiring that state to be explicitly set
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.
The session callback can be a Python function or a PL/SQL procedure.
There are three common scenarios for
- 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.
- When using Database Resident Connection Pooling (DRCP): use a PL/SQL callback with tagging.
sessionCallback parameter is a Python procedure, it will be called
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 initSession(connection, requestedTag): cursor = connection.cursor() cursor.execute("ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI'") # Create the pool with session callback defined pool = cx_Oracle.SessionPool("hr", userpwd, "orclpdb1", sessionCallback=initSession, encoding="UTF-8") # Acquire a connection from the pool (will always have the new date format) connection = pool.acquire()
If needed, the
initSession() 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
In this example tagging was not being used, so the
Note: 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
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;""")
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.
When cx_Oracle is using Oracle Client libraries 12.2 or later, then cx_Oracle
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
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 initSession(connection, requestedTag): if requestedTag == "NLS_DATE_FORMAT=SIMPLE": sql = "ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD'" elif requestedTag == "NLS_DATE_FORMAT=FULL": sql = "ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI'" cursor = connection.cursor() cursor.execute(sql) connection.tag = requestedTag pool = cx_Oracle.SessionPool("hr", userpwd, "orclpdb1", sessionCallback=initSession, encoding="UTF-8") # Two connections with different session state: connection1 = pool.acquire(tag = "NLS_DATE_FORMAT=SIMPLE") connection2 = pool.acquire(tag = "NLS_DATE_FORMAT=FULL")
See SessionCallback.py for an example.
When cx_Oracle 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
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
In cx_Oracle set
sessionCallback to the name of the PL/SQL procedure. For
pool = cx_Oracle.SessionPool("hr", userpwd, "dbhost.example.com/orclpdb1:pooled", sessionCallback="myPlsqlCallback", encoding="UTF-8") connection = pool.acquire(tag="NLS_DATE_FORMAT=SIMPLE", # DRCP options, if you are using DRCP cclass='MYCLASS', purity=cx_Oracle.ATTR_PURITY_SELF)
See SessionCallbackPLSQL.py for an example.
Heterogeneous and Homogeneous Connection Pools¶
By default, connection pools are ‘homogeneous’, meaning that all connections
use the same database credentials. However, if the pool option
is False at the time of pool creation, then a ‘heterogeneous’ pool will be
created. This allows different credentials to be used each time a connection
is acquired from the pool with
When a heterogeneous pool is created by setting
homogeneous to False and no
credentials are supplied during pool creation, then a user name and password
may be passed to
acquire() as shown in this example:
pool = cx_Oracle.SessionPool(dsn="dbhost.example.com/orclpdb1", homogeneous=False, encoding="UTF-8") connection = pool.acquire(user="hr", password=userpwd)
Database Resident Connection Pooling (DRCP)¶
Database Resident Connection Pooling (DRCP) enables database resource sharing for applications 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.
Applications can choose whether or not to use pooled connections at runtime.
For efficiency, it is recommended that DRCP connections should be used in conjunction with cx_Oracle’s local connection pool.
Using DRCP in Python
Using DRCP with cx_Oracle applications involves the following steps:
- Configuring and enabling DRCP in the database
- Configuring the application to use a DRCP connection
- Deploying the application
Configuring and enabling DRCP
Every instance of Oracle Database uses a single, default connection
pool. The pool can be configured and administered by a DBA using the
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
set a single parameter:
EXECUTE DBMS_CONNECTION_POOL.ALTER_PARAM( pool_name => 'SYS_DEFAULT_CONNECTION_POOL', param_name => 'MAX_THINK_TIME', param_value => '1200')
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.
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
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, 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:
Once enabled this way, the pool automatically restarts when the database
instance restarts, unless explicitly stopped with the
The pool cannot be stopped while connections are open.
Application Deployment for DRCP
In order to use DRCP, the
purity parameters should
be passed to
cclass is not set, the pooled server sessions will not be reused optimally,
and the DRCP statistic views will record large values for NUM_MISSES.
purity can be one of
ATTR_PURITY_DEFAULT. The value
ATTR_PURITY_SELF allows reuse of
both the pooled server process and session memory, giving maximum benefit from
DRCP. See the Oracle documentation on benefiting from scalability.
Using Oracle’s Easy Connect syntax, the connection would look like:
connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com/orcl:pooled", encoding="UTF-8")
Or if you connect using a Net Service Name named
connection = cx_Oracle.connect("hr", userpwd, "customerpool", encoding="UTF-8")
Then only the Oracle Network configuration file
to be modified:
customerpool = (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp) (HOST=dbhost.example.com) (PORT=1521))(CONNECT_DATA=(SERVICE_NAME=CUSTOMER) (SERVER=POOLED)))
If these changes are made and the database is not actually configured for DRCP, or the pool is not started, then connections will not succeed and an error will be returned to the Python application.
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.
The example below shows how to connect to Oracle Database using Database Resident Connection Pooling:
connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com/orcl:pooled", cclass="MYCLASS", purity=cx_Oracle.ATTR_PURITY_SELF, encoding="UTF-8")
The example below shows connecting to Oracle Database using DRCP and cx_Oracle’s connection pooling:
mypool = cx_Oracle.SessionPool("hr", userpwd, "dbhost.example.com/orcl:pooled", encoding="UTF-8") connection = mypool.acquire(cclass="MYCLASS", purity=cx_Oracle.ATTR_PURITY_SELF)
Python scripts where cx_Oracle connections do not go out of scope quickly
(which releases them), or do not currently use
should be examined to see if
close() can be used, which
then allows maximum use of DRCP pooled servers by the database:
# Do some database operations connection = mypool.acquire(cclass="MYCLASS", purity=cx_Oracle.ATTR_PURITY_SELF) . . . connection.close(); # Do lots of non-database work . . . # Do some more database operations connection = mypool.acquire(cclass="MYCLASS", purity=cx_Oracle.ATTR_PURITY_SELF) . . . connection.close();
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 are:
DBA_CPOOL_INFO displays configuration information about the DRCP pool. The
columns are equivalent to the
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
INACTIVE otherwise. Note 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
V$SESSION view shows information about the currently active DRCP
sessions. It can also be joined with
V$SESSION.PADDR = V$PROCESS.ADDR to correlate the views.
V$CPOOL_STATS view displays information about the DRCP statistics for
an instance. The V$CPOOL_STATS view can be used to assess how efficient the
pool settings are. T his example query shows an application using the pool
effectively. The low number of misses indicates that servers and sessions were
reused. The wait count shows just over 1% of requests had to wait for a pooled
server to become available:
NUM_REQUESTS NUM_HITS NUM_MISSES NUM_WAITS ------------ ---------- ---------- ---------- 10031 99990 40 1055
cclass was set (allowing pooled servers and sessions to be
reused) then NUM_MISSES will be low. If the pool maxsize is too small for
the connection load, then NUM_WAITS will be high.
V$CPOOL_CC_STATS 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$cpool_cc_stats; CCLASS_NAME NUM_REQUESTS NUM_HITS NUM_MISSES -------------------------------- ------------ ---------- ---------- HR.MYCLASS 100031 99993 38
V$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$CPOOL_CONN_INFO to, for example, identify
misconfigured machines that do not have the connection class set correctly.
This view maps the machine name to the class name:
SQL> SELECT cclass_name, machine FROM v$cpool_conn_info; CCLASS_NAME MACHINE --------------------------------------- ------------ CJ.OCI:SP:wshbIFDtb7rgQwMyuYvodA cjlinux . . .
In this example you would examine applications on
cjlinux and make
cclass is set.
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.
The following proxy examples use these schemas. The
mysessionuser schema is
granted access to use the password of
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 = cx_Oracle.connect("myproxyuser", "myproxyuserpw", "dbhost.example.com/orclpdb1", encoding="UTF-8") # PROXY_USER: None # SESSION_USER: MYPROXYUSER # Basic Authentication with a proxy connection = cx_Oracle.connect(user="myproxyuser[mysessionuser]", "myproxyuserpw", "dbhost.example.com/orclpdb1", encoding="UTF-8") # PROXY_USER: MYPROXYUSER # SESSION_USER: MYSESSIONUSER
Pooled connection examples:
# Basic Authentication without a proxy pool = cx_Oracle.SessionPool("myproxyuser", "myproxyuser", "dbhost.example.com/orclpdb1", encoding="UTF-8") connection = pool.acquire() # PROXY_USER: None # SESSION_USER: MYPROXYUSER # Basic Authentication with proxy pool = cx_Oracle.SessionPool("myproxyuser[mysessionuser]", "myproxyuser", "dbhost.example.com/orclpdb1", homogeneous=False, encoding="UTF-8") 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.
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.
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
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.
First create a new wallet as the
mkstore -wrl "/home/oracle/wallet_dir" -create
This will prompt for a new password for the wallet.
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/orclpdb1 myuser myuserpw
Method 2 - Using a connect name identifier:
mkstore -wrl "/home/oracle/wallet_dir" -createCredential mynetalias myuser myuserpw
The alias key
mynetaliasimmediately following the
-createCredentialoption 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
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 = orclpdb1) ) )
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.
Add the following wallet location entry in the sqlnet.ora file, using the
DIRECTORYyou 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.
Ensure the configuration files are in a default location or set 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 = cx_Oracle.connect(dsn="mynetalias", encoding="UTF-8")
pool = cx_Oracle.SessionPool(externalauth=True, homogeneous=False, dsn="mynetalias", encoding="UTF-8") pool.acquire()
dsn must match the one used in the wallet.
After connecting, the query:
SELECT SYS_CONTEXT('USERENV', 'SESSION_USER') FROM DUAL;
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 = cx_Oracle.connect(user="[mysessionuser]", dsn="mynetalias", encoding="UTF-8") # PROXY_USER: MYUSER # SESSION_USER: MYSESSIONUSER
Pooled connection example:
# External Authentication with proxy pool = cx_Oracle.SessionPool(externalauth=True, homogeneous=False, dsn="mynetalias", encoding="UTF-8") pool.acquire(user="[mysessionuser]") # PROXY_USER: MYUSER # SESSION_USER: MYSESSIONUSER
The following usage is not supported:
pool = cx_Oracle.SessionPool("[mysessionuser]", externalauth=True, homogeneous=False, dsn="mynetalias", encoding="UTF-8") pool.acquire()
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.
Login to your computer. The commands used in these steps assume the operating system user name is “oracle”.
Login to SQL*Plus as the SYSTEM user and verify the value for the
SQL> SHOW PARAMETER os_authent_prefix NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ os_authent_prefix string ops$
Create an Oracle database user using the
os_authent_prefixdetermined 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 = cx_Oracle.connect(dsn="mynetalias", encoding="UTF-8")
Your session user will be
If your database is not on the same computer as python, you can perform testing
by setting the database configuration parameter
Beware this is insecure.
See Oracle Database Security Guide for more information about Operating System Authentication.
mode parameter of the function
the database privilege that you want to associate with the user.
The example below shows how to connect to Oracle Database as SYSDBA:
connection = cx_Oracle.connect("sys", syspwd, "dbhost.example.com/orclpdb1", mode=cx_Oracle.SYSDBA, encoding="UTF-8") cursor = con.cursor() sql = "GRANT SYSOPER TO hr" cursor.execute(sql)
This is equivalent to executing the following in SQL*Plus:
CONNECT sys/syspwd AS SYSDBA GRANT SYSOPER TO hr;
Securely Encrypting Network Traffic to Oracle Database¶
You can encrypt data transferred between the Oracle Database and the Oracle Client libraries used by cx_Oracle so that unauthorized parties are not able to view plain text values as the data passes over the network. The easiest configuration is Oracle’s native network encryption. The standard SSL protocol can also be used if you have a PKI, but setup is necessarily more involved.
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, on either the database server and/or on each cx_Oracle ‘client’ machine. 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
$ORACLE_HOME/network/admin/sqlnet.ora file. Set the checksum negotiation
to always validate a checksum and set the checksum type to your desired value.
The network encryption settings can similarly be set. For example, to use the
SHA512 checksum and AES256 encryption use:
SQLNET.CRYPTO_CHECKSUM_SERVER = required SQLNET.CRYPTO_CHECKSUM_TYPES_SERVER = (SHA512) SQLNET.ENCRYPTION_SERVER = required SQLNET.ENCRYPTION_TYPES_SERVER = (AES256)
If you definitely know that the database server enforces integrity and
encryption, then you do not need to configure cx_Oracle separately. However
you can also, or alternatively, do so depending on your business needs. Create
sqlnet.ora on your client machine and locate it with other
Optional Oracle Net Configuration Files:
SQLNET.CRYPTO_CHECKSUM_CLIENT = required SQLNET.CRYPTO_CHECKSUM_TYPES_CLIENT = (SHA512) SQLNET.ENCRYPTION_CLIENT = required SQLNET.ENCRYPTION_TYPES_CLIENT = (AES256)
The client and server sides can negotiate the protocols used if the settings indicate more than one value is accepted.
Note that these are example settings only. You must review your security requirements and read the documentation for your Oracle version. In particular review the available algorithms for security and performance.
NETWORK_SERVICE_BANNER column of the database view
V$SESSION_CONNECT_INFO can be used to verify the
encryption status of a connection.
For more information on Oracle Data Network Encryption and Integrity, configuring SSL network encryption and Transparent Data Encryption of data-at-rest in the database, see Oracle Database Security Guide.
After connecting, passwords can be changed by calling
# Get the passwords from somewhere, such as prompting the user oldpwd = getpass.getpass("Old Password for %s: " % username) newpwd = getpass.getpass("New Password for %s: " % 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
of the function
# Get the passwords from somewhere, such as prompting the user oldpwd = getpass.getpass("Old Password for %s: " % username) newpwd = getpass.getpass("New Password for %s: " % username) connection = cx_Oracle.connect(username, oldpwd, "dbhost.example.com/orclpdb1", newpassword=newpwd, encoding="UTF-8")
Connecting to Autononmous Databases¶
To enable connection to Oracle Autonomous Database in Oracle Cloud, a wallet needs be downloaded from the cloud GUI, and cx_Oracle needs to be configured to use it. A database username and password is still required. The wallet only enables SSL/TLS.
Install the Wallet and Network Configuration Files¶
From the Oracle Cloud console for the database, download the wallet zip file. It contains the wallet and network configuration files. Note: keep wallet files in a secure location and share them only with authorized users.
Unzip the wallet zip file.
For cx_Oracle, 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
The other files and the wallet password are not needed.
Place these files as shown in Optional Oracle Net Configuration Files.
Run Your Application¶
tnsnames.ora file contains net service names for various levels of
database service. For example, if you create a database called CJDB1 with the
Always Free services from the Oracle Cloud Free Tier, then you might decide to use the
connection string in
Update your application to use your schema username, its database password, and a net service name, for example:
connection = cx_Oracle.connect("scott", userpwd, "cjdb1_high", encoding="UTF-8")
Once you have set Oracle environment variables required by your application,
TNS_ADMIN, you can start your application.
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 Transaction Processing Dedicated Deployments manual.
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. Successful connection depends on specific proxy configurations. Oracle does not recommend doing this when performance is critical.
sqlnet.ora and add a line:
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:
- cjdb1_high = (description=
- (address= (https_proxy=myproxy.example.com)(https_proxy_port=80) (protocol=tcps)(port=1522)(host= … )
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.
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
maxSessionsPerShard 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 = cx_Oracle.connect("hr", userpwd, "dbhost.example.com/orclpdb1", encoding="UTF-8", shardingkey=["SCOTT"])
Numbers keys can be used in a similar way:
connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com/orclpdb1", encoding="UTF-8", shardingkey=)
When sharding by DATE, you can connect like:
import datetime d = datetime.datetime(2014, 7, 3) connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com/orclpdb1", encoding="UTF-8", shardingkey=[d])
When sharding by RAW, you can connect like:
b = b'\x01\x04\x08'; connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com/orclpdb1", encoding="UTF-8", shardingkey=[b])
Multiple keys can be specified, for example:
keyArray = [70, "SCOTT", "gold", b'\x00\x01\x02'] connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com/orclpdb1", encoding="UTF-8", shardingkey=keyArray)
A super sharding key example is:
connection = cx_Oracle.connect("hr", userpwd, "dbhost.example.com/orclpdb1", encoding="UTF-8", supershardingkey=["goldclass"], shardingkey=["SCOTT"])