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Oracle RDBMS Server Articles

Three impossibilities with partitioned indexes

There are three restrictions on indexing and partitioning: a unique index cannot be local non-prefixed; a global non-prefixed index is not possible; a bitmap index cannot be global. Why these limitations? I suspect that they are there to prevent us from doing something idiotic.

Are older releases of the database really unsupported?

I see posts on Oracle related forums about various releases (anything that isn't 11.x or 12.x) being "unsupported". This is wrong. Of course you should upgrade any 9i or 10g databases, but you don't have to.

Oracle Database 12c: New Features - Pluggable Databases

mikerajendran's picture

Oracle Database 12c: New Features – Pluggable Databases by Michael Rajendran

Introduction

Oracle has leap forwarded the middleware technologies especially the database technology into the cloud. So far Oracle has been the traditional RDBMS database suitable for the private enterprise data centers within corporate walls.

“ORA-01081: cannot start already-running ORACLE” While creating a new Database

Hi Geeks,

When I was doing a research on Oracle Database creation, through DBCA, last week, I came across a very interesting scenario which I couldn’t stop sharing with you :)

I have a cluster of machines (don’t confuse it with a RAC cluster but just a group of machines required for my application deployment) with 11.2.0.2 installed and a Database instance running.

I got a requirement to remove everything accumulated in the machine as a result of the Oracle installation and the Database creation: The installation directories, the datafiles, oratab entries etc…

After removing all th

1Z0-052 Oracle DBA Admin 1 OCA Study Guide by Matthew Morris: Review

Matthew Morris (who makes many constructive and knowledgeable contributions to the forum) has written a series of study guides for the OCA/OCP exams. I asked him if I could have a copy of one to review. The result: it's very good. This is a copy of the review I put up on Amazon.

How to move a table from one schema to another

The other day, I was asked how to move a table from one schema to another. The answer, as we all know, is "you can't do that: you have to create a new table as a copy of the old one, or use export/import. It will take a long long time." Not true.

Oracle Data Guard 11g – Overview Client Failover Configuration

Reference partitioning and partitionwise joins

Why do you sometimes not get partitionwise joins? Because the optimizer isn't clever enough. Reference partitioning has many benefits, one of which is that the optimizer understands it. You will always get a partitionwise join if your tables are reference partitioned.

Progress status of an index rebuild or creation, or other long operations.

David Lozano Lucas's picture

When we launch a long operation, such as a RMAN backup or rebuild of a large index, we can come to despair of not having an estimate of the time it may take. We can even come to think that is doing nothing.

For the progress of a long operation we can query the view V$SESSION_LONGOPS, first obtaining the process ID from V$SESSION. In the case of DBA, we know exactly which user is rebuilding the index, so we can simplify it into a single query.

The following example shows the progress of the reconstruction of a partition of an index.

Constraints and performance: you want as many constraints as possible

Several times I have had to deal with people who do not want to define constraints. I have never understood why they don't, because my experience is that the more constraints you can define, the better Oracle will perform. If anyone knows where the idea that not defining constraints is a Good Thing comes from, I would be interested to know.

Following are two very simple examples of constraints allowing the optimizer to develop better plans.

First, foreign key constraints. These give the optimizer a lot of information about the data that may mean it can cut out whole tables from a query.