Ways to access Oracle Database in PostgreSQL

tar -xvf unixODBC-2.3.4.tar.gz
cd unixODBC-2.3.4/
./configure --sysconfdir=/etc
make
make install

Binary/Libraries/configuration files location: /usr/local/bin,/usr/local/lib,/etc(odbc.ini,odbcinst.ini)

Install Oracle ODBC Driver

rpm -ivh oracle-instantclient11.2-basic-11.2.0.4.0-1.x86_64.rpm
rpm -ivh oracle-instantclient11.2-odbc-11.2.0.4.0-1.x86_64.rpm
rpm -ivh oracle-instantclient11.2-devel-11.2.0.4.0-1.x86_64.rpm

Binary/Libraries location: /usr/lib/oracle/11.2/client64

tar -zxvf ODBC-Link-1.0.4.tar.gz
cd ODBC-Link-1.0.4
export PATH=/opt/PostgreSQL/9.5/bin:$PATH
which pg_config 
make USE_PGXS=1
make USE_PGXS=1 install

Libraries and SQL files location: /opt/PostgreSQL/9.5/share/postgresql/contrib

Installation will create a ODBC-Link module SQL file in $PGHOME/contrib directory. Load the SQL file, which will create a schema by name “odbclink” with necessary functions in it.

psql -p 5432 -d oratest -U postgres -f /opt/PostgreSQL/9.5/share/postgresql/contrib/odbclink.sql

At this point, we have installed unixODBC Drirver, Oracle ODBC driver and ODBC-Link module for PostgreSQL. As a first step, we need to create a DSN using Oracle ODBC.

Edit /etc/odbcinst.ini file and pass the drivers deifinition

## Driver for Oracle
[MyOracle]
Description     =ODBC for oracle
Driver          =/usr/lib/oracle/11.2/client64/lib/libsqora.so.11.1
UsageCount=1
FileUsage = 1
Driver Logging = 7

Edit /etc/odbc.ini file and create the DSN with driver mentioned in /etd/odbcinst.ini

## Host: pg.raghav-node1.com, PORT: 1521
## Oracle Instance Name: ORA11G, Username: mmruser, Password: mmruser
## ODBC Data source: Ora

[Ora]
Description = myoracledb database
Driver = MyOracle
Trace = yes
TraceFile = /tmp/odbc_oracle.log
Database = //pg.raghav-node1.com:1521/ORA11G
UserID = mmruser
Password = mmruser
Port = 1521

After creating DSN, load all Oracle & unix ODBC driver libraries by setting environment variables and test the connectivity using OS command line tool “dltest” & “iSQL”

[[email protected] ~]# export ORACLE_HOME=/usr/lib/oracle/11.2/client64
[[email protected] ~]# export LD_LIBRARY_PATH=/usr/local/unixODBC-2.3.4/lib:/usr/lib/oracle/11.2/client64/lib
[[email protected] ~]# export ODBCINI=/etc/odbc.ini
[[email protected] ~]# export ODBCSYSINI=/etc/
[[email protected] ~]# export TWO_TASK=//pg.raghav-node1.com:1521/ORA11G
[[email protected] ~]# dltest /usr/lib/oracle/11.2/client64/lib/libsqora.so.11.1
SUCCESS: Loaded /usr/lib/oracle/11.2/client64/lib/libsqora.so.11.1
[[email protected] ~]# isql ora -v
+---------------------------------------+
| Connected!                            |
|                                       |
| sql-statement                         |
| help [tablename]                      |
| quit                                  |
|                                       |
+---------------------------------------+
SQL>

Now, set the same environment variables for postgres user for loading the libraries and restart the PostgreSQL cluster to take effect. Connect to PostgreSQL and call odbclink functions to connect to Oracle database.

[[email protected] ~]#su - postgres
[[email protected] ~]$ export ORACLE_HOME=/usr/lib/oracle/11.2/client64
[[email protected] ~]$ export LD_LIBRARY_PATH=/usr/local/unixODBC-2.3.4/lib:/usr/lib/oracle/11.2/client64/lib
[[email protected] ~]$ export ODBCINI=/etc/odbc.ini
[[email protected] ~]$ export ODBCSYSINI=/etc/
[[email protected] ~]$ export TWO_TASK=//pg.raghav-node1.com:1521/ORA11G
[[email protected] ~]$ dltest /usr/lib/oracle/11.2/client64/lib/libsqora.so.11.1
SUCCESS: Loaded /usr/lib/oracle/11.2/client64/lib/libsqora.so.11.1
[[email protected] ~]$ /opt/PostgreSQL/9.5/bin/pg_ctl -D /opt/PostgreSQL/9.5/data/ stop -mf
[[email protected] ~]$ /opt/PostgreSQL/9.5/bin/pg_ctl -D /opt/PostgreSQL/9.5/data/ start
[[email protected] ~]$ psql
psql.bin (9.5.2)
Type "help" for help.

postgres=# select odbclink.connect(‘DSN=Ora’);
connect
———
1
(1 row)

Cool right…!!!. For retrieving and manipulating data refer to ODBC-Link README file.

Using Foreign DataWrappers

An SQL/MED(SQL Management of External Data) extension to the SQL Standard allows managing external data stored outside the database. SQL/MED provides two components Foreign data wrappers and Datalink. PostgreSQL introduced Foreign Data Wrapper(FDW) in 9.1 version with read-only support and in 9.3 version write support of this SQL Standard. Today, the latest version has a number of features around it and many varieties of FDW available to access different remote SQL databases.

Oracle_fdw provides an easy and efficient way to access Oracle Database. IMO,its one of the coolest method to access the remote database. To compile Oracle_FDW with PostgreSQL 9.5, we need Oracle Instant Client libraries and pg_config set in PATH. We can use the same Oracle Instant Client libraries used for ODBC-Link. Let’s see how it works.

First, set environment variables with OIC libraries and pg_config

export PATH=/opt/PostgreSQL/9.5/bin:$PATH
export ORACLE_HOME=/usr/lib/oracle/11.2/client64
export LD_LIBRARY_PATH=/usr/lib/oracle/11.2/client64/lib

Unzip the oracle_fdw module and compile it with PostgreSQL 9.5

unzip oracle_fdw-1.4.0.zip
cd oracle_fdw-1.4.0/
make 
make install

Now switch as ‘postgres’ user and restart the cluster by loading Oracle Instant Client libraries required for oracle_fdw extension and create the extension inside the database.

[[email protected] 9.5]$ export ORACLE_HOME=/usr/lib/oracle/11.2/client64/lib
[[email protected] 9.5]$ export LD_LIBRARY_PATH=/usr/lib/oracle/11.2/client64/lib:$LD_LIBRARY_PATH
[[email protected] 9.5]$ /opt/PostgreSQL/9.5/bin/pg_ctl -D /opt/PostgreSQL/9.5/data/ stop -mf
[[email protected] 9.5]$ /opt/PostgreSQL/9.5/bin/pg_ctl -D /opt/PostgreSQL/9.5/data/ start
[[email protected] 9.5]$ psql
Password:
psql.bin (9.5.2)
Type "help" for help.

postgres=# create extension oracle_fdw;
CREATE EXTENSION

Now you can access the Oracle database.

postgres=# CREATE SERVER oradb FOREIGN DATA WRAPPER oracle_fdw OPTIONS (dbserver '//pg.raghav-node1.com/ORA11G');
CREATE SERVER
postgres=# GRANT USAGE ON FOREIGN SERVER oradb TO postgres;
GRANT
postgres=# CREATE USER MAPPING FOR postgres SERVER oradb OPTIONS (user 'scott', password 'tiger');
CREATE USER MAPPING
postgres=#
postgres=# CREATE FOREIGN TABLE oratab (ecode integer,name char(30)) SERVER oradb OPTIONS(schema 'SCOTT',table 'EMP');
CREATE FOREIGN TABLE
postgres=# select * from oratab limit 3;
 ecode |              name
-------+--------------------------------
  7369 | SMITH
  7499 | ALLEN
  7521 | WARD
(3 rows)

Using Oracle Call Interface(OCI) Drivers

Oracle Call Interface(OCI) a type-2 driver freely available on Oracle site which allows the client to connect to Oracle database. EDB Postgres Advanced Server (also called EPAS) a proprietary product has built-in OCI-based database link module called dblink_ora, which connects to Oracle database using Oracle OCI drivers. All you have to do to use dblink_ora module, install EPAS(not covering installation) and tell EPAS where it can find Oracle OCI driver libraries. We can make use of same Oracle Instant Client by specifying its libraries location in LD_LIBRARY_PATH environment variable and to take effect restart the EPAS cluster.

First, switch as “enterprisedb” user, load the libraries and restart the cluster. That’s all, we are good to access Oracle database.

[[email protected] ~]$ export LD_LIBRARY_PATH=/usr/lib/oracle/11.2/client64/lib
[[email protected] bin]$ /opt/PostgresPlus/9.5AS/bin/pg_ctl -D /opt/PostgresPlus/9.5AS/data/ restart
[[email protected] bin]$ psql
psql.bin (9.5.0.5)
Type "help" for help.

edb=# select dblink_ora_connect(‘oraconn’,’localhost’,’edbora’,’edbuser’,’edbuser’,1521);
dblink_ora_connect
——————–
OK
(1 row)

Note: EPAS connects to the Oracle Database using Oracle Instant Client library “libclntsh.so”. If you won’t find the library in Oracle Client Library location then create the symbolic link with libclntsh.so pointing to the libclntsh.so.version.number. Refer to documentation.

In the example, dblink_ora_connect establishes a connection to an Oracle database with the user-specified connection information. Later using link name(‘oraconn’ in my case) we can perform operations like SELECT,INSERT,DELETE,UPDATE & COPY using dblink_ora* functions. All functions you can refer from the EnterpriseDB documentation here.

All the above methods will be very handy if you are working on migration projects. Hope its helpful. Thank you

–Raghav