DataStorage

Question 1

What is a database page (block)?

Answer 1

A fixed-size block of data that serves as the fundamental unit of data storage and transfer in a DBMS

Question 2

What is the typical size range of database pages?

Answer 2

512 bytes to 32 kilobytes

Question 3

What are the three key rules for database pages?

Answer 3

1) Pages contain only one type of data 2) A record cannot span multiple pages 3) No record is larger than a page

Question 4

What are fixed-length records?

Answer 4

Records where all fields have a predefined fixed size

Question 5

What is the main advantage of fixed-length records?

Answer 5

Simplicity in record access and management

Question 6

What are the two main problems with fixed-length records?

Answer 6

1) Records may cross block boundaries 2) Difficult to delete records

Question 7

What is a slotted page header?

Answer 7

A header containing number of record entries end of free space and location/size of each record

Question 8

What are the two components of variable-length record storage?

Answer 8

1) Initial part with fixed-length information 2) Contents of variable-length attributes

Question 9

How are variable-length attributes represented?

Answer 9

Using a pair (offset length) where offset shows where data begins and length shows size in bytes

Question 10

What is a null-value bitmap?

Answer 10

A bitmap that indicates which attributes have NULL values in a record

Question 11

What are the two main solutions for storing Large Objects (LOBs)?

Answer 11

1) Segmentation (breaking into smaller pieces) 2) File System Storage

Question 12

What is heap file organization?

Answer 12

Records are placed anywhere in the file where space is available

Question 13

What is sequential file organization?

Answer 13

Records are stored in sequential order based on a search key

Question 14

What is multitable clustering file organization?

Answer 14

Records from multiple related tables are stored in the same file

Question 15

What is a free-space map?

Answer 15

Array with one entry per block indicating the fraction of block that is free

Question 16

Why is writing free-space map to disk periodically better than immediately?

Answer 16

Writing immediately for every update would be very expensive

Question 17

What are the five main types of file organization?

Answer 17

Heap Sequential B+-tree Hashing Multitable clustering

Question 18

What is table partitioning?

Answer 18

Dividing records into smaller relations typically based on attribute values

Question 19

What is the data dictionary?

Answer 19

System catalog that stores metadata about the database

Question 20

What are the main components of a database buffer system?

Answer 20

Buffer (portion of main memory) and Buffer manager (subsystem for allocation)

Question 21

What is a pinned block?

Answer 21

A block that cannot be evicted from buffer because it’s being read by a process

Question 22

What is the difference between S and X locks?

Answer 22

S (shared) locks for reading X (exclusive) locks for updating only one process can get X lock

Question 23

What is LRU replacement policy?

Answer 23

Removes the block that hasn’t been accessed for the longest time

Question 24

What is MRU replacement policy?

Answer 24

Removes the most recently used block

Question 25

What is toss-immediate strategy?

Answer 25

Frees block space as soon as final tuple is processed

Question 26

What is column-oriented storage?

Answer 26

Storage method where each column is stored separately instead of storing rows together

Question 27

What are the main benefits of column-oriented storage?

Answer 27

Reduced I/O better compression improved CPU cache performance vector processing

Question 28

What are the main drawbacks of column-oriented storage?

Answer 28

Costly tuple reconstruction complex updates decompression overhead

Question 29

What type of workload is column-oriented storage best suited for?

Answer 29

OLAP (Online Analytical Processing) workloads

Question 30

What is the pin count used for in buffer management?

Answer 30

Tracks multiple concurrent pinning operations to prevent premature block eviction

Question 31

Why don’t databases rely on OS for memory management?

Answer 31

OS uses FIFO policy which isn’t efficient for data-processing systems that know their workflow