Communication between two databases (Oracle, VirtualBox) - oracle

Question

Currently I am trying to understand how can two databases communicate to each other (for instance: get data from one to another).
Detailed description
I have two Oracle databases, one on Windows and latter on Oracle VirtualBox. On Windows DB I have one user (PAI) with single table called TESTME. On VirtualBox, only user (PAI_VB) was created. Now, I want to display the content of the TESTME table from SQL Developer from VB.
I have done
I want to display table TESTME using LINK statement:
CREATE DATABASE LINK LINK_TO_PAI
CONNECT TO PAI IDENTIFIED BY PAI
USING 'DESCRIPTION = (ADDRESS=(PROTOCOL=TCP)(HOST=myIP)(PORT=1521))
(CONNECT_DATA=(SERVICE_NAME=XE))';
Note: data from 'DESCRIPTION' section were taken from tnsname.ora file on Windows.
Having that, via following query I will manage to display table:
SELECT * FROM PAI.TESTME#LINK_TO_PAI;
Unfortunately, it does not work.
Error from console
ORA-12154: TNS:could not resolve the connect identifier specified
12154. 00000 - "TNS:could not resolve the connect identifier specified"
*Cause: A connection to a database or other service was requested using
a connect identifier, and the connect identifier specified could not
be resolved into a connect descriptor using one of the naming methods
configured. For example, if the type of connect identifier used was a
net service name then the net service name could not be found in a
naming method repository, or the repository could not be
located or reached.
*Action:
- If you are using local naming (TNSNAMES.ORA file):
- Make sure that "TNSNAMES" is listed as one of the values of the
NAMES.DIRECTORY_PATH parameter in the Oracle Net profile
Questions
Could you please propose solution to my problem (I know that in *Action section there is a hint but still I cannot solve it).
Maybe, you could introduce me another way to make communication between two databases possible.
EDIT
I managed to connect from my VB machine to one on Win10 via SQLDeveloper and SQLPlus. Unfortunately, using Oracle LINK I can not access data from database.
SOLVED !!
I managed to solve my issue. The problem laid in LINK. Since following part:
'DESCRIPTION = (ADDRESS=(PROTOCOL=TCP)(HOST=myIP)(PORT=1521))
(CONNECT_DATA=(SERVICE_NAME=XE))'
was inside tnsnames.ora file i should define my link as follows:
CREATE DATABASE LINK LINK_TO_PAI
CONNECT TO PAI IDENTIFIED BY PAI
USING 'xe';
After that minor change, I was able to freely us LINK in my example. Cheers :)

Answer 1

Here's what you need to have for a working database link:
Network connectivity between the two hosts.
Oracle Listener process running on the host you want to connect to.
Correct TNS entry while creating the link.
Correct username and password to connect to the remote database.
The TNS-12154 error you're getting means the database running on the virtual host can't get to XE's listener using the description you gave it.
Make sure you're using the correct IP address when trying to connect to your Windows host from your virtual machine.
Run tnsping from your virtual environment to see if it can get to the Windows host listener.
tnsping 'DESCRIPTION = (ADDRESS=(PROTOCOL=TCP)(HOST=your_windows_host_ip_from_step_1)(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=XE))'
or just tnsping XE if you have the TNS entry stored as XE in tnsnames.ora file on your virtual machine.
See also: Oracle documentation — Testing Connections.
Once you get OK response from tnsping try connecting to XE with sqlplus (sqlplus PAI/PAI#XE) or via SQL Developer running on the virtual host. If you can connect that way your database link should also work with the same TNS entry.

Answer 2

This is a tricky part of oracle because there are a number of diverent ways to make a connection.
I suggest that you begin to make sure that you have a tnsnames.ora file both on windows and in your virtualbox environment. What os are you running in VirtualBox by the way?
In both tnsnames.ora files both databases should be named. Easiest to make them identical.
Then connect with sql*plus from windows to your database in VirtualBox and from VirtualBox to your database on Windows.
Just to make sure your network and tns config are OK.
If this works recreate your db-link with the servce alias from tnsnames after using. This should work.