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Oracle Indexes

Myth: Bitmap Indexes With High Distinct Columns (Blow Out)

I just couldn’t resist.   One of the great myths in Oracle is that bitmap indexes are only suitable and should only be used with columns that have so-called low cardinality (few distinct) values. A classic example of this myth being propagated is in this latest Burleson news item, “Oracle bitmap index maximum distinct values“, from Feb 16 [...]

How Does An Execution Plan Suddenly Change When The Statistics (And Everything Else) Remains The Same ? (In Limbo)

I’ve slipped this post in as there have been a number of discussions recently on how execution plans have changed while nothing else appears to have changed in the database. How can an execution plan suddenly change when no one has made any changes to the database ?   By no changes, it means that there [...]

Index Block Dumps and Index Tree Dumps Part I: (Knock On Wood)

I thought before I jump into a topic that requires looking at a number of index block dumps, it might be worth briefly recapping how one goes about dumping index blocks in Oracle.   A block dump is simply a formatted representation of the contents of a particular Oracle database block.  Although I’ll be focusing [...]

The CPU Costing Model – A Few Thoughts Part II

As previously discussed, the formula used by the CBO using the CPU costing model is basically:
 
(sum of all the single block I/Os x average wait time for a single block I/O +
 sum of all the multiblock I/Os x average wait time for a multiblock I/O +
 sum of all the required CPU cycles / CPU cycles per second)
/
average [...]

2 Year Anniversary !!

A little anniversary slipped by unnoticed this past weekend. Which isn’t really too surprising considering how busy things have been lately, with Christmas just around the corner.
I’ve now been at this blogging lark for 2 whole years !!
Hopefully, there are a few people out there just that little bit wiser now regarding how indexes work [...]