Also, a great resource is the Oracle Concepts Guide:
Specifically the section on Intro to Indexes
http://download.oracle.com
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Question
Database Indexes
I am preparing for interviews and wondering to see if I can collect some consolidated knowledge on database indexes ?
Just wondering if some one can answer or point to appropriate resources for the the following -
Indexing
Types of Indexing
Clustered Indexing
Indexing Algorithms for database
Differences and Advantages and disadvantages of each.
Thank You,
Jagadeesh.
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Answers
check this link...
http://www.careerride.com/
There are some tips (not so known!) about indexing:
1. Indexes speed up SELECT but speed down DML operations
2. When not to use indexes: small tables, more then 2-4% of the rows extracted by the SELECT, rare used SELECT
3. Indexes do not work (are not considered by the Optimizer) prior collecting statistics over the table and the indexes
4. After bulk changes the DBA should collect statistics again
There are other details, but the above mentioned (by the Experts) sources are good base.
I concur with mrjoltcola on Tom Kyte books.
Another great author, particularly on indexes is Richard Foote
http://richardfoote.wordpr
in particular, I recommend this (it's gets pretty deep, but well worth the effort)
http://richardfoote.files.
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by: mrjoltcolaPosted on 2009-09-24 at 21:29:15ID: 25420030
Unless you have some specific questions, the best book I can recommend is "anything by Tom Kyte", I own all of them.
Expert Oracle Database Architecture, Tom Kyte
http://www.amazon.com/Expe
I promise you, if you order it, wait the 3-4 days for shipping, then spend a couple of evenings reading it, you'll learn all you want to know.
Otherwise some basics.
1) The standard index is the B-Tree
2) Clustered indexing in Oracle is a bit different than other databases. Oracle has Index Organized Tables (IOT) which is akin to SQL Server / Sybase's single table cluster index. It is the ordering of table rows by the index key. In Oracle an index cluster can be a multi-table cluster that stores rows of multiple tables by a shared key (so table joins can actually use a single scan).
3) Hash indexing can result in faster random access, but less efficient in range searches and more storage overhead. B-Tree indexes are ordered by key, so work well for range scans when ordering by the index key. Bitmap indexing works well for low-cardinality columns but are bad for concurrent access and also may need frequent rebuilding after a lot of changes