The top advice from Oracle experts in 2008

Whether you have a question about Oracle errors, backups, upgrades or jobs, SearchOracle.com has an expert panel ready to help. This year our experts answered questions on all these topics and more - - here's a look back at some of our most popular expert questions and answers of 2008.

TABLE OF CONTENTS
1. What is the ORA-03113 error?
2. How to get history of modified data from Oracle databases
3. How DDL and DML commands work in Oracle
4. How to do a hot backup when Oracle Database is up
5. When should an Oracle database be reorganized?
6. Tips for how to size an Oracle server
7. When to use CHECK constraints in SQL
8. When to do a manual upgrade vs. export and import
9. What is the difference between a database engineer, architect and administrator?
10. How to archive and decommission a database

What is the ORA-03113 error?
Q: We have an Oracle 10g database and get the ORA-03113 error sporadically. This is a science application where we query time-series data from a vb.net application. We can query successfully all day with some parameters (location, variable identifier, and date range) but when the date range changes beyond a (arbitrary?) limit (e.g. 2003 to 2007 works every time, but 2002 to 2007 fails every time), this error appears. We get a similar error using Oracle's sqldeveloper, though the error message text is different. Where do we start looking for answers?

A: ORA-3113 errors mean that your network connection to the database was severed. In my experience, there are two problem areas. One, something in the network failed between the client and the database. Two, a bug in the database caused the session to be terminated and the client thinks a network error was the cause. If you are sure your network is fine, then it is probably a bug. Make sure you have the 10.2.0.3 patchset installed. After that, file a Service Request with Oracle Support. Only they will be able to help you with the ORA-3113 error.


What is the ORA-03113 error?
Q: How can you get the history of data modified from an Oracle database?

A: There are a few options at your disposal. After the fact, you can mine your archived redo logs using Oracle's Log Miner utility. Before the fact, you can set up auditing to record changes...


How DDL and DML commands work in Oracle
Q: What happens in the background when we execute DDL or DML commands?

A: First, Oracle parses the statement and ensures that the statement is syntactically correct and semantically correct. Next, Oracle verifies that the user has permissions to perform the statement. If the user can execute the statement, Oracle obtains all locks necessary for the statement to complete. Once the locks have all been obtained, Oracle executes the statement. In some cases, results are returned. If results are returned from the statement, Oracle fetches those results and places the result set in an area called a 'cursor'. The cursor is passed back to the application.


Hot backup when Oracle Database is up
Q: What is the procedure for doing a hot backup when the database is up?

A: There are two ways. The preferred way with Oracle's databases today is to use RMAN. The following will perform a hot backup using RMAN.
Read expert Brian Peasland's recommended steps for using RMAN and learn more about RMAN and hot backups.

When should an Oracle database be reorganized?
Q: When should a database be reorganized?

A: Never. A well-designed database should never need reorganization. It used to be that a DBA would perform a weekly or monthly reorg to help database performance. But today's Oracle databases do not need regularly scheduled reorgs to perform well. Bad design can throw this theory out the window though.

Tips for how to size an Oracle server
Q: Do you have any suggestions on where I can find the following information, with recommended server hardware specifications for how to size an Oracle server? I'll be using storage area network (SAN) storage.
Number of processors
Quantity of RAM

I've searched the Oracle site and even though there are a number of white papers, I haven't seen anything like the old 9i sizing guide.

A: I have not seen any sites or other pieces of information that would give you the information that you seek. And I would be leery of the information presented. The amount of memory, processors, and other system resources are not dictated by the total volume of data in the database.

CHECK constraints
Q: How can I create a constraint to not allow a date prior to 1 Jan 2007 to be entered?

A: This is accomplished with a CHECK constraint. Here's an example:
create table documents
( id integer not null primary key
, title varchar(99) not null
, added date not null
, constraint only_new_ones
check ( added>= '2007-01-01' )
);

Manual upgrade vs. export and import
I am ready to upgrade. My database size is 200gb and it is an unsupported version of Oracle to upgrade to 10g(8.1.6.2 to 10g). It's O/S is on HP-UX, so could you tell me whether the best process for upgrade is to follow the manual upgrade process or by using the export & import to the new Oracle Database? If I follow the manual method then I have to apply the 8i to 8i Patches then to 10g . If I follow exp/imp then I need more down time. Which process should I follow?

A: If you perform the manual upgrade process, then you will have to be at least at Oracle 8.1.7 before you can begin. So to go from 8.1.6.2 to 10g, you will need two upgrades with this path. If you use export/import, then you will only need one upgrade. On average, each manual upgrade will take about 1 hour, but this time can vary. So without knowing more about your environment, the manual upgrade process will require about 2 hours of downtime. Using export/import for a 200GB database will probably take longer. So the big question to answer here is how much downtime can you take for the upgrade? If you had a larger downtime window, then you might use exp/imp for the upgrade. The exp/imp method also lets you perform some reorganization like moving objects to new tablespaces.

What is the difference between a database engineer, architect and administrator?
Q: Could you please explain the differences between a database engineer, a database architect and a database administrator?

A: Great question! It can get pretty confusing as these titles (and many more including database developer, data architect, data analyst, data modeler, database designer, etc.) are often intermixed, used improperly, or redefined by the companies using them. The definition really depends on the actual job descriptions as defined by the various companies posting them. I will do my best, however, to differentiate and simplify them for you...

How to archive and decommission a database
Q: What would be the best way to archive and decommission a 5GB Oracle 7.3 Database? This data needs to be available for at least 20 years from now in case a regulatory agency requires it, and we are afraid that in the future we won't be able to recover it to a newer version of Oracle.

A: I use Oracle's export utility for this type of task. Your database isn't too large, so exp will work. The nice thing about exp is that future versions of Oracle will still be able to read the resulting dump file. So perform the following:
exp userid=system/manager file=my_db.dmp log=my_db.log full=y

The resulting files can then be written to DVD or some other media for long term storage.

Source: Shayna Garlick @ searchoracle.techtarget.com

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