Data Storage & Organization

Question 1

What is transfer size?

Answer 1

the unit of memory that can be individually accessed, read and written

Question 2

What is latency?

Answer 2

the time it takes for info to be delivered after the initial request is made

Question 3

What is bandwidth?

Answer 3

The rate at which info can be delivered.

Question 4

What is Processor cache?

Answer 4

Faster memory storing recently used data that reduces the average memory access time.

Question 5

What is a Solid State Drive?

Answer 5

• uses flash memory for storage

Question 6

What is RAID (Redundant Arrays of Independent Disks) ?

Answer 6

a disk organization technique that utilize a large number of inexpensive, mass-market disks to provide increased reliability, performance and storage.

Question 7

What do RAIDs do?

Answer 7

store extra data incase of disk failure.

• Mirror or shadow
• duplicates entires disks on multiple disks

Question 8

What is mean time to failure (MTTF)?

Answer 8

the average time the device is expected to run continuously without any failure.

Question 9

Explain RAID Level 0

and what is its capacity?

Answer 9

Striping at the block level (non-redundant)

• used for high performance where data loss is not crucial (parallesism)

Capacity: N

Question 10

Explain RAID Level 1 and what is its capacity?

Answer 10

Mirrored disks (redundancy)

• for apps that require redundancy (protection from disk failure)

Capacity: N/2

Question 11

Explain RAID Level 2

Answer 11

Memory-Style-Error-Correcting-Codes with bit stripping

Question 12

Explain RAID Level 5 and what is its capacity?

Answer 12

• offers both reliability & increased performance

Capacity: N-1

Question 13

Explain RAID Level 6 and what is its capacity?

Answer 13

• offers extra redundancy compared to Level 5
• used to deal with multiple drive failures

Capacity: N - X
X = # of parity drives such as 2)

Question 14

What is a block-level interface

Answer 14

Allows the program to read & write a chunk of memory called a block (or page) from the device

Question 15

What is a byte-level interface

Answer 15

allows the program to read & write individually addressable bytes from the device

Question 16

What is a file-level interface

Answer 16

abstracts away the device addressable characteristics & provides a standard byte-level interface for files to programs running on the OS

Question 17

Hierarchy of a database

Answer 17

Database is made up of files

• each file contains blocks
• each block contains records
• each record contains fields
• each field is a representation of a data item in a record

Question 18

What does a record consist of?

Answer 18

One or more fields grouped together

Question 19

What are the two main types of records? And what are they?

Answer 19

1. Variable-length records: the size of the record varies

2. Fixed-length records: all records have the same size

Question 20

4 situations where variable formats are useful

Answer 20

1. The data doesn’t have a regular structure in most cases
2. The data values are sparse in the records
3. There are repeating fields in the records
4. The data evolves quickly so schema evolution is challenging

Question 21

3 disadvantages of variable formats

Answer 21

1. Waste space by repeating schema info for every record
2. Allocating variable-sized records efficiently is challenging
3. Query processing is more difficult and less efficient when the structure of the data varies

Question 22

What are the 6 issues related to storing records in blocks? Describe each one.

Answer 22

1. Separation
   - how do we separate adjacent records
2. Spanning
   - can a record cross a block boundary?
3. Clustering
   - can a block cross a block boundary?
4. Splitting
   - are records allocated in multiple blocks?
5. Ordering
   - are the records sorted in any way?
6. Addressing
   - how do we reference a given record?

Question 23

What are the 2 options when records do not fit in a block?

Describe them

Answer 23

Unspanned
- waste space at the end of the block

Spanned
- Start a records at the end of a block and continue on the next

Question 24

What is clustering?

6 storing issues

Answer 24

allocating records of different types together on the same block (or same file) cause they are frequently accessed together.

Question 25

What is split record?

6 storing issues

Answer 25

a records where portions of the record are allocated on multiple blocks for reasons other than spanning

Question 26

What is ordering records

6 storing issues

Answer 26

when the records in a file (block) are sorted based on the value of one or more fields

Question 27

What are the 2 methods of ordering records, describe them.

6 storing issues

Answer 27

1. Physically ordered
   - the records are allocated in blocks in sorted order
2. Logical ordered
   - the records are not physical sorted, but each records contains a pointer to the next in the sorted order

Question 28

What is addressing records?

6 storing issues

Answer 28

A method for defining a unique value or address to reference a particular record

Question 29

What are the 2 methods of addressing records, describe them.
(6 storing issues)
(Think ordering records)

Answer 29

1. Physically addressed
   - a record has a physical address based on the device where its located
2. Logically addressed
   - A record has a key value or some other identifier that can be used to lookup its physical address

Question 30

What is pointer swizzling?

Answer 30

the process for converting disk pointers to memory pointers and vice versa when blocks move between memory and disk

Question 31

What is a buffer and a buffer manager?

Answer 31

A buffer is a portion of main memory available to store copies of disk blocks

A buffer manager is a subsystem responsible for allocating buffer space in main memory

Question 32

What is buffer replacement strategy ?

Answer 32

determines which block should be removed from the buffer when space is required