Search

Top 60 Oracle Blogs

Recent comments

Clustering Factor

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 [...]

Cost of Virtual Indexes (Little Lies)

I’ve previously discussed Virtual Indexes and how they can be used to do basic “what if” analysis if such an index really existed. However, a recent comment on the OTN forums regarding using them to compare index costs made me think a follow-up post regarding the dangers of Virtual Indexes might be warranted. The big advantage of [...]

Dynamic Sampling And Indexes

There is a lot more to say about Dynamic Sampling and indexes, and I'll try to cover these basics in my Dynamic Sampling series on AllThingsOracle.com, but two recent discussions on the OTN forums and on Charles Hooper's blog prompted me to publish this blog post.

These discussions revolved around the following issues with Dynamic Sampling and indexes:

1. CREATE INDEX On Empty Table

Why Is My Index Not Being Used Solution (Eclipse)

Well done to everyone that got the correct answer Indeed, the subtle but significant difference between the two demos was that demo one created the table in a tablespace called USER_DATA with manual segment space management (with freelists/freelist groups set to 1), while demo two created the table in a tablespace called USER_DATA1 with automatic segment space management. [...]

Rebuilding Indexes and the Clustering Factor Solution (Move On)

Excellent !! This quiz created quite a bit of debate and it was nice to sit back and read some interesting discussions. The Clustering Factor is basically the measurement of how well aligned the data in the underlining table is in relation to the index and is the number of table related I/Os required to read the entire table via a [...]

Rebuilding Indexes and the Clustering Factor Quiz (One Of The Few)

Today’s question has been prompted by various recent comments regarding the Clustering Factor (CF) of an index and how to change the CF requires a reorg of the underlining table. It used to be quite a common myth that if the CF of an index was greater that “X” or based on some nonsensical formula the [...]

Concatenated Bitmap Indexes Part I (Two Of Us)

Although Bitmap Indexes are commonly created on one column, you can create multi-column, concatenated Bitmap indexes as well.   Many of the same issues and factors in deciding to create a single, multi-column index vs. several, single column indexes apply to Bitmap indexes as they do with B-Tree indexes, although there are a number of [...]

Myth: Bitmap Indexes With High Distinct Columns (Supermassive Black Hole)

As discussed in my previous post, it’s a silly myth to suggest a bitmap index should only be used for so-called “low cardinality” columns else the resultant index would be “huge”. I thought it might be worth a quick refresh to see a simple little demonstration why such claims are a nonsense.  There is in fact no limit to [...]