Chapter 27 Flashcards
In which situation index slows down database performance mostly
When database is write-intensive
What are the two ways to access data
- non-keyed access
- keyed access
Does Non-keyed access uses index
No
What are special index structures
Inverted index
Bitmap index
Cluster index
Join index
What is inverted index
An inverted index is an optimized structure that is built primarily for retrieval, with update being only a secondary consideration.
Does search engines uses inverted index
Yes
What is the worst case of inverted index
O(n)
What are Bitmap Indexes
Index consists of a number of bitmaps
What is length of the bit vector
The length of the bit vector is the number of records in the base table.
Does bitmaps are good for high-cardiniality
No
What are advantages of Bitmap Index
Very low storage space
What is faster in database retrieval, bitmap index or B-tree index
bitmap index
What is the disadvantage of bitmap Index
Locking of many rows
What is Cluster Index
A cluster index defines the sort order on the base table. The big advantage of a cluster index is that all the rows with the same cluster index value will be placed into adjacent locations in a small number of data blocks like a cluster.
When Cluster Index is best
O (n log n)
