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Data Warehouse Design Mistakes 1: Lack of Foreign Key Constraints

This post is part of a series that discusses some common issues in data warehouses.

Refreshing Materialized Views with Referential Integrity Constraints

I have a number of tables on a reporting system which have referential integrity constraints, and whose contents are replicated from a primary system. I am going to create materialized views on these prebuilt tables to manage incremental refresh. However, the referential integrity means that some materialized view will have to be refreshed before others which refer to them.

Indexing Foreign Key Constraints With Invisible Indexes (Invisible People)

In my previous post I discussed when deleting rows from parent tables, how Bitmap Indexes based on the FK constraint can prevent the expensive Full Tables Scans (FTS) on the child tables but not the associated exclusive table locks. Last year, I discussed how it was possible in Oracle Database 12c to have multiple indexes on the same column list. […]

Indexing Foreign Key Constraints With Bitmap Indexes (Locked Out)

Franck Pachot made a very valid comment in my previous entry on Indexing Foreign Keys (FK) that the use of a Bitmap Index on the FK columns does not avoid the table locks associated with deleting rows from the parent table. Thought I might discuss why this is the case and why only a B-Tree index does […]

Indexing Foreign Keys (Helden)

A recent question on an internal forum asked whether an index on a Foreign Key (FK) constraint designed to avoid locking issues associated with deletes on the parent tables needs to precisely match the columns in the FK. Could the columns in the index potentially be a different order or be appended with additional columns ? The answer is […]

Oracle11g: New Locking Modes When Policing FK Constraints (A Wolf at the Door)

As I’ve been focusing mainly with Oracle 11g at work these days, thought I might look at a number of Oracle 11g related topics in the coming weeks.   To start with, there’s been a subtle but potentially significant change introduced in Oracle 11g (since 11.1.0.6) with regard to the manner in which locks are [...]

An Essay on Science

Richard Feynman defined science as "the belief in the ignorance of experts." Science begins by questioning established ideas. ...Even those ideas promoted by so-called experts.

The value of science that's obvious to everybody is the chance you might discover some valuable truth that nobody else has discovered before. That's the glamorous idea that might motivate you to begin the hard work that science sometimes requires. Science is also valuable to you when you learn that an established idea, no matter how much you may not like it, really is true after all. That second value of science is not as glamorous, but it's just as important. My little prayer with respect to that possibility is, "If an idea I believe is wrong, please let me find out before anybody else does."

Everyone can do science. Not just "scientists"; all of us. But you need to do science "right," or it's not science. Do it right, and you accumulate a little bit of truth. Do it wrong, and and you've wasted your time, or worse, you've doomed yourself to waste more of your time in the future, too.

The difference between "right" and "wrong" in science is not some snooty, bureaucratic concept. You don't need a license or a blessing to do science right. You just need to ensure that the cause-effect relationships you choose to believe are actually correct. One of the rules for doing science right is that you measure instead of just asserting your opinion.

Different people have different thresholds of skepticism. Some people believe new ideas, whether they're true or false, with very little persuasion. The people who are persuaded easily to believe false things cannot contribute much useful new knowledge to their communities (irrespective of how much they might publish).