Java Solutions: 2020

Monday, October 26, 2020

How to find out all the Java versions installed on a linux machine?

Use the command below to get all the java versions installed.

update-alternatives --display java

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Tuesday, October 20, 2020

Crystal Reports: ORA-12170: TNS:Connect timeout occurred [Database Vendor Code: 12170]

In the SAP Crystal Reports editor, you open the Database Expert and trying to view/edit the command, after you have entered your database login credentials you received the following error.

This can be caused by several issues. The following are some of the ways to fix it.

1. ping the database machine to make sure you can access that machine.

2. Check if the database host of your Oracle Instant Client is using the correct IP address. If you are accessing the database on a remote machine, localhost or 127.0.0.1 will not work.

a. Open your Control Panel.

b. Open the Administrative Tools window.

c. Right-click on the ODBC Data Sources and open it.

d. Select the System DSN tab to look for the Driver used by your data source.

e. Select the Drivers tab and locate your driver.

f. Open a file explorer, go to Program Files (x86)\Oracle Instant Client\<your driver>.

g. Open the tnsnames.ora file in a text editor, change the HOST = <the correct database IP address>

3. Make sure the firewall is not blocking the connection.

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Friday, October 9, 2020

ORA-27125: unable to create shared memory segment; Error: 28: No space left on device

You got the below error when starting up the Oracle database.

SQL> STARTUP

ORA-27125: unable to create shared memory segment

Linux-x86_64 Error: 28: No space left on device

Additional information: 3760

Additional information: 4278190080

This occurs when the Kernel parameter kernel.shmall is too small.

Follow the steps below to fix the problem.

1. Determine the page size.

> getconf PAGE_SIZE

4096

2. Determine the Total System Global Area (SGA).

SQL> SHOW SGA

Total System Global Area 6442450944 bytes

Fixed Size 2938792 bytes

Variable Size 3892316248 bytes

Database Buffers 2533359616 bytes

Redo Buffers 13836288 bytes

3. Calculate the recommended value for shmall.

shmall = SGA / PAGE_SIZE

With SGA = 6 GB and PAGE_SIZE = 4096, the shmall is

shmall = 6 * 1024 * 1024 * 1024 / 4096 = 1572864

4. Update the kernel.shmall parameter.

> vi /etc/sysctl.conf

Scroll down to find kernel.shmall and change it's value to 1572864.

* If you could not find the SGA at step 2, you may try to double the current value of shmall.

5. Apply the change.

> sysctl -p

6. Verify the value.

> cat /proc/sys/kernel/shmall

1572864

7. Login to the Oracle database as sysdba and start the database.

SQL> STARTUP

ORACLE instance started.

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Friday, September 25, 2020

Use clob column in the where clause in an Oracle database; ORA-00932: inconsistent datatypes: expected - got CLOB

There are several ways to fix the ORA-00932: inconsistent datatypes: expected - got CLOB exception.

Let's say you have a clobColumn in the clobTable with the CLOB datatype. You can use it in the WHERE clause of a select, update, or delete statement by one of the following ways.

1. Use the dbms_lob.compare method

SELECT * from clobTable

WHERE dbms_lob.compare(clobColumn, to_clob('<the value of the column>')) = 0

2. If the clobColumn value is less than 4000 characters, you can use the to_char function.

SELECT * from clobTable

WHERE to_char(clobColumn) = '<the value of the column>';

3. Use like instead of equal.

SELECT * from clobTable

WHERE clobColumn like '<the value of the column>';

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Sunday, September 20, 2020

java.sql.SQLException: Listener refused the connection with the following error: ORA-12505, TNS:listener does not currently know of SID given in connect descriptor

You received such a error when you started to connect to your Oracle database via JDBC.

java.sql.SQLException: Listener refused the connection with the following error:
ORA-12505, TNS:listener does not currently know of SID given in connect descriptor

at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:673)
at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:715)
at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:385)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:30)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:564)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
at com.tds.db.DB.connectToDB(DB.java:118)

This means that the TNS listener is running, but it cannot connect you to the database. It may due to:

the database has not been started up,
the database has not registered with the listener, e.g. because the database was started before the listener. (When the database starts, it registers itself with a listener if it is already running. If the listener isn't running, the database doesn't register itself, and if the listener starts, it doesn't go looking for databases that might register with it.)

To fix the problem:

1. login as the oracle user

>$ su - oracle

enter your oracle user password

2. Execute the below command

>$ lsnrctl status

If you see these in your output:

Services Summary...

Service "your database service" has 1 instance(s).

Instance "your database service", status READY, has 1 handler(s) for this service...

It means that your database is up and running.

3. Login to sqlplus as sysdba

>$ sqlplus /NOLOG

SQL> connect / as sysdba;

4. If your database is not running according to step 2, start the database.

SQL> STARTUP

5. Register the listener

SQL> conn system

SQL> alter system set local_listener = 'ADDRESS=(PROTOCOL=TCP)(HOST=localhost)(PORT=1521)' scope = both;

SQL> alter system register;

SQL> quit

6. Check to see if things are right.

$ lsnrctl status

You should see something like below.

LSNRCTL for Linux: Version 12.1.0.2.0 - Production on 18-SEP-2020 17:32:34

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost)(PORT=1521)))

STATUS of the LISTENER

------------------------

Alias LISTENER

Version TNSLSNR for Linux: Version 12.1.0.2.0 - Production

Start Date 02-SEP-2020 16:12:28

Uptime 16 days 1 hr. 20 min. 6 sec

Trace Level off

Security ON: Local OS Authentication

SNMP OFF

Listener Parameter File /12c/app/oracle/product/12.1.0/db_1/network/admin/listener.ora

Listener Log File /12c/app/oracle/diag/tnslsnr/oraclelog/listener/alert/log.xml

Listening Endpoints Summary...

(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=oracleserver)(PORT=1521)))

(DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))

(DESCRIPTION=(ADDRESS=(PROTOCOL=tcps)(HOST=oracleserver)(PORT=5500))(Security=(my_wallet_directory=/12c/app/oracle/admin/db/xdb_wallet))(Presentation=HTTP)(Session=RAW))

Services Summary...

Service "your database service" has 1 instance(s).

Instance "your database service", status READY, has 1 handler(s) for this service...

Service "oracleXDB" has 1 instance(s).

Instance "your database service", status READY, has 1 handler(s) for this service...

The command completed successfully

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Monday, July 6, 2020

git in NetBeans: Contains files that are in conflict - Solved

After you switch to a different branch, you notice that there is a red cylinder mark next to the project icon. When you hover over it, a message shows up and it says "Contains files that are in conflict".

To fix it, right-click on the project, choose Git, then Resolve Conflict.

In the pop-up window, choose either Remove File From Index or Keep Current File Content.

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Wednesday, July 1, 2020

PostgreSQL: add an interval of days represented by a variable to a date

We know that if you want to add 4 days to a date, you do the following.

<your date> + interval '4 days'

However, if you have

int x = 4;

It will not work by:

<your date> + interval 'x days'

The way to make it work is:

<your date> + x * (interval '1 day')

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