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John Watson's blog

The COST column of EXPLAIN PLAN

The COST column cannot be used to compare execution plans. Punkt.

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 Database 11g Release 2: Performance Tuning Tips and Techniques (Richard Niemiec)

I've been asked by the publishers to review "Oracle Database 11g Release 2: Performance Tuning Tips and Techniques" by Richard Niemiec of TUSC. Conclusion: it is good but not perfect. This is an extended version of the review I put up on Amazon.

Please use ANSI join syntax

The old Oracle join syntax really should be consigned to history.

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.

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.

Hints on OCA/OCP exam technique

Part of my job is teaching for Oracle University, and I'm often asked about OCP exam technique. Here are a few hints. The OCM exam is very different, and the confidentiality rules forbid me from discussing it, so please don't ask.

11.2 Grid Infrastructure networking enhancements

This note is an attempt to summarize some of the 11gR2 facilities that allow for greater virtualization of resources, reducing reliance on networking facilities supplied by the operating system. All corrections welcome.