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Oracle Cost Based Optimizer

Clustering Factor Calculation Improvement Part II (Blocks On Blocks)

My previous post on the new TABLE_CACHED_BLOCKS statistics gathering preference certainly generated some interest My blog hits for the week have gone off the charts !! One of the concerns raised by this new capability was that setting such a preference might result in really unrealistic and inaccurate Clustering Factor (CF) values, especially for those […]

Important !! Clustering Factor Calculation Improvement (Fix You)

Believe me, this article is worth reading I’m currently not allowed to discuss Oracle 12c Database goodies but I am allowed to discuss things perhaps initially intended for 12c that are currently available and already back-ported to 11g. This includes a wonderful improvement in the manageability of how the Clustering Factor (CF) of an index can now […]

Concatenated Bitmap Indexes Part II (Everybody’s Got To Learn Sometime)

A basic little post to conclude this discussion. The issues regarding whether to go for single column indexes vs. concatenated indexes are similar for Bitmap indexes as they are for B-Tree indexes.   It’s generally more efficient to access a concatenated index as it’s only the one index with less processing and less throwaway rowids/rows [...]

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 [...]

The CPU Costing Model: A Few Thoughts Part V (Reality)

There’s plenty more I could talk about regarding the CBO CPU costing model and system statistics but I’ll make this my final little comment on this subject for now.   As previously discussed, the CPU costing model basically takes the time it takes to perform the all necessary I/O related activities and all the time it takes to [...]

The CPU Costing Model: A Few Thoughts Part IV (Map of the Problematique)

It’s called the CPU Costing model because among other things, it includes the time associated with performing CPU operations.   The CPU Costing model formula once again:   (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 [...]

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 [...]

The CPU Costing Model: A Few Thoughts Part I

In the coming days, I’ll post a series of little entries highlighting a specific point in relation to the use of system statistics and the CPU cost model. In my previous post, we looked at how the cost of a FTS is calculated using the CPU costing model and how this generally results in an increase in the associated FTS [...]