Fixing Common Oracle Database Problems

Lots of businesses use Oracle databases to keep their important stuff. These databases mostly work fine, but yeah, sometimes they run into issues. Anyone who's worked with Oracle knows the feeling when things go wrong.

Don't worry, though — these problems happen to everyone. Most fixes are actually pretty easy once you know what you are doing. I'll show you the usual Oracle headaches and how to fix them.

1. The "Snapshot Too Old" Error (ORA-01555)

What's Happening

Oracle is basically saying, "I can't remember what that data looked like anymore" when your query runs too long.

Why It Happens

• Oracle already overwrote the old data it was keeping for reference.
• Your query is taking longer than Oracle is set to remember things.
• You are committing changes too often in a loop.

How to Fix It

• Tell Oracle to remember things longer.
  SQL

   

  ALTER SYSTEM SET UNDO_RETENTION = 2000;

• Don't put COMMIT statements inside loops.
• Improve the performance of the queries by adding appropriate indexes.

2. The "Resource Busy" Error (ORA-00054)

What's Happening

You are trying to update something that someone/process is already using.

Why It Happens

Another user or process has locked the table or row you want.

How to Fix It

• Find out who is blocking it.
  SQL

   

  SELECT 
       s1.sid AS blocked_session_id,
       s1.serial# AS blocked_serial_num,
       s1.username AS blocked_user,
       s1.machine AS blocked_machine,
       s1.blocking_session AS blocking_session_id,
       s1.sql_id AS blocked_sql_id
  FROM 
       v$session s1
  WHERE 
       s1.blocking_session IS NOT NULL
  ORDER BY 
       s1.blocking_session;

• If needed, kill the process or just tell Oracle to wait a bit instead of giving up right away.
  SQL

   

  ALTER SYSTEM KILL SESSION 'sid, serial#' IMMEDIATE;

3. Sudden Disconnection Error (ORA-03113)

What's Happening

Your connection to the database dropped unexpectedly.

Why It Happens

• Network issues
• The database crashed or restarted
• Software bugs

How to Fix It

• Keep an eye on logs for alerts and make sure the database has not crashed.
• Look at the trace files for clues.
• Make sure your network is stable.
• Update Oracle if it's a known bug.

4. Permission Denied Error (ORA-01031)

What's Happening

Oracle won't let you do something because you don't have permission.

Why It Happens

Your user account doesn't have the right privileges.

How to Fix It

• Get the permission you need.
  SQL

   

  GRANT CREATE TABLE TO username;

• For looking at someone else's data.
  SQL

   

  GRANT SELECT ON hr.employees TO app_user;

5. Password Expired Error (ORA-28001)

What's Happening

The user's password has expired.

Why It Happens

Oracle is enforcing password expiration rules.

How to Fix It

• Reset the password:
  SQL

   

  ALTER USER username IDENTIFIED BY new_password;

• Or stop passwords from expiring.
  SQL

   

  ALTER PROFILE DEFAULT LIMIT PASSWORD_LIFE_TIME UNLIMITED;

6. Can't Connect Error (ORA-12154)

What's Happening

Oracle doesn't understand how to connect to the database you are asking for.

Why It Happens

The connection info is wrong or missing in your setup files.

How to Fix It

• Check your tnsnames.ora file for mistakes.
• Make sure the service name matches.
• Try the simple connection format instead.

sqlplus user/password@//host:port/service_name

7. No More Space Error (ORA-01653)

What's Happening

You can't add more data because you are out of space.

Why It Happens

Your database file is full and cannot grow automatically.

How to Fix It

• Add another data file:
  SQL

   

  ALTER TABLESPACE users ADD DATAFILE '/path/users10.dbf' 
  SIZE 250M AUTOEXTEND ON MAXSIZE 500M;

• Let your existing file grow automatically.
  SQL

   

  ALTER DATABASE DATAFILE '/path/users11.dbf' RESIZE 500M;

• Keep an eye on your space.
  SQL

   

  SELECT tablespace_name, used_space, tablespace_size
  FROM dba_tablespace_usage_metrics;

8. Internal Error (ORA-00600)

What's Happening

Oracle came across a problem that it doesn’t know how to handle.

Why It Happens

• Memory or data corruption
• Hardware failures
• Incompatible parameter settings

How to Fix It

• Run DBVERIFY or ANALYZE commands to check if the database is corrupted; if so, then it has to be restored from the backup.
• Work with Oracle support and share the logs and errors to help debug.

9. Super Slow Queries

What's Happening

This is a common problem where the query performance degrades with an increase in data.

Why It Happens

• Poorly written SQL
• Missing indexes
• Outdated statistics
• Running the queries without filters

How to Fix It

• See how Oracle is running your query.
  SQL

   

  EXPLAIN PLAN FOR type_your_query_here;
  SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

• Add indexes where needed.
• WHERE clauses should be used properly to return the correct result.
• Update the statistics.
  SQL

   

  EXEC DBMS_STATS.GATHER_TABLE_STATS('schema', 'table_name');

10. Corrupted Data

What's Happening

Part of your database file got corrupted or damaged.

Why It Happens

• Hardware failures
• Sudden shutdowns
• Software bugs

How to Fix It

• Find the bad blocks.
  SQL

   

  SELECT * FROM v$database_block_corruption;

• Use RMANto repair them.
  SQL

   

  RMAN> BLOCKRECOVER DATAFILE 5 BLOCK 233 TO 245;

• Mark blocks that can't be fixed.
  SQL

   

  EXEC DBMS_REPAIR.ADMIN_TABLES(TRUE, FALSE, 'REPAIR_TABLE');

11. High CPU Usage by Oracle Applications

What's Happening

Oracle is using too much CPU and slowing everything down.

Why It Happens

• Inefficient queries
• Missing indexes
• Too many background processes

How to Fix It

• Find the queries that consume high CPU.
  SQL

   

  SELECT * FROM v$sql ORDER BY cpu_time DESC FETCH FIRST 20 ROWS ONLY;

• Fix those queries.
• Run performance reports if you have the license.
• Consider moving old data to archives.

Tips to Avoid Problems

• Always have backups. This is the key to any database management as the system can always be reverted to avoid any data loss.
• Update statistics regularly. Oracle needs current info to work well
• Check logs often. Catch problems early by analyzing the logs periodically
• Test before production. Try changes in a test/stage environment first so that the majority of issues are caught before promoting the code to prod.
• Set up automatic health checks. Schedules can help keep everything aligned by running the processes on time.

Conclusion

Working with Oracle databases gets easier with practice. A lot of the problems you will run into are just the same few issues that everyone deals with. 

The more you work with these issues, the faster you'll spot and fix them. Hopefully, this article makes your database work a little easier and less stressful.