Lecture 4

Question 1

What are disadvantages of static hasing?

Answer 1

If data file has a lot of deletions, a lot of space gets wasted. Conversely, if a file grows a lot, long overflow chains develop

Question 2

In extendible hashing, what do we do with the directory once we receive a collision?

Answer 2

Double the size of it

Question 3

In extendible hashing when do collisions occur and how do we handle them?

Answer 3

When data entries have the same value. We handle them through overflow pages

Question 4

In extendible hashing, how many I/O’s are needed?

Answer 4

If directory can fit in main memory, only 1, otherwise multiple.

Question 5

What is heap file bad at?

Answer 5

Equality Search and deletion

Question 6

What is sorted file bad at?

Answer 6

Insert and Delete

Question 7

What is unclustered hash and idnex bad at?

Answer 7

Scan and Range search

Question 8

What is index only evaluation?

Answer 8

Answering a query by using ONLY the index

Question 9

What is a composite key? What are the advantages and disadvantages?

Answer 9

In the case of indexing, when we have a search key with 2 query parameters. Allows for more index only evaluations.

However they are costly to maintain because they need more updates and take up more space

Question 10

What is a bitmap index and when is it useful?

Answer 10

When we use bits to determine what the value of a row is.
On columns that have a few values (ex: boolean)

Question 11

What is a spatial index used for?

Answer 11

Geospatial queries, GIS.