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Clustering Factor

Rebuilding Indexes: Danger With Clustering Factor Calculation (Chilly Down)

Let me start by saying if you don’t already following Jonathan Lewis’s excellent Oracle blog, do yourself a favour. In a recent article, Jonathan highlighted a danger with rebuilding indexes (or indeed creating an index) when used in relation to collecting index statistics with the TABLE_CACHED_BLOCKS preference. I’ve discussed the importance of the TABLE_CACHED_BLOCKS statistics […]

Answer: Anything Wrong With Query Performance? (Red Right Hand)

I of course attract a highly clever readership :). As some have commented, for a single table to require 1000+ consistent gets to retrieve 1000 rows implies that each row needs to be accessed from a different block. This in turn implies the Clustering Factor for this index to be relatively bad and the associated […]

Improve Data Clustering on Multiple Columns Concurrently (Two Suns in the Sunset)

I’ve had a couple of recent discussions around clustering and how if you attempt to improve the clustering of a table based on a column, you thereby ruin the current clustering that might exist for a different column. The common wisdom being you can only order the data one way and if you change the […]

12.2 Online Conversion of a Non-Partitioned Table to a Partitioned Table (A Small Plot Of Land)

In my previous post, I discussed how you can now move heap tables online with Oracle Database 12.2 and how this can be very beneficial in helping to address issues with the Clustering Factor of key indexes. A problem with this technique is that is requires the entire table to be effectively reorganised when most of […] Introduction to Attribute Clustering (The Division Bell)

One of the really cool new features introduced in is Attribute Clustering. This new table based attribute allows you to very easily cluster data in close physical proximity based on the content of specific columns. As I’ve discussed many times, indexes love table data that is physically clustered in a similar manner to the index … … Continue reading

Clustering Factor Calculation Improvement Part III (Too Much Rope)

In my previous post, I discussed how for larger tables that really do have randomised data, not even setting the new TABLE_CACHED_BLOCKS to its 255 maximum value is going to make any real difference to the resultant Clustering Factor (CF) of an index. The 255 maximum value here protects us somewhat from abusing this capability […]

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 […]

Storage Indexes vs Database Indexes Part II: Clustering Factor (Fast Track)

Two posts in two days !! Well, with Christmas just around the corner, I thought I better finish off a couple of blog posts before I get fully immersed in the festive season The Clustering Factor (CF) is the most important index related statistic, with the efficiency of an index performing multi-row range scans very much […]

Indexes vs. Full Table Scan: Picture vs. 1000 Words (Pictures Of Lily)

I’m in the process of writing a number of new presentations and in one I’ve included a favorite little graph of mine that I’ve used over the years to help illustrate the relationship between the cost of using an index vs. the cost of using a Full Table Scan (FTS). It’s occurred to me that I’ve never actually [...]