Lecture 2

Question 1

What is the difference between non-volatile memory and volatile.

Answer 1

Volatile memory keeps data after the device has shutdown, whilst non-volatile memory looses the data

Question 2

Is data directly accessed on disks?

Answer 2

No, data is accessed through RAM. RAM gets data from main memory.

Question 3

What system allows DBMS to interact with both Hard disks and SSD’s

Answer 3

File System

Question 4

Does in-memory DMBS use the same architecture as traditional DMBS?

Answer 4

No.

Question 5

Identify the difference between Platters, Tracks, Blocks and Sectors.

Answer 5

Platter: Disk.
Tracks: ring within a disk.
Sector: A part of a Track.
Block: The unit that describes the data between RAM and hard disk

Question 6

What is data striping and which RAID level uses it?

Answer 6

Data striping: Same data, store it on multiple smaller disks, increasing speed. RAID 0

Question 7

What is data Mirroring and which RAID level uses it?

Answer 7

Data mirroring: storing copies of the data on multiple, same sized, disks. RAID 1

Question 8

What is RAID 0 + 1?

Answer 8

Striping + Mirroring

Question 9

What does RAID level 2 do?

Answer 9

Computes and stores data in separate disks that help in error detection and recovery

Question 10

What does a disk space manager do?

Answer 10

Manages space on the disk, attempting to store pages on subsequent blocks. Lowest Level of Software. Hides details of underlying software.

Question 11

How does the Disk Space Manager use page ids with allocating and deallocating?

Answer 11

When allocating, the DSM will assign a free block to a page ID.
When deallocating, the DSM will use the page ID to deallocate the block

Question 12

What are the 2 ways Disk Space Managers keep track of free blocks? Which one is generally better?

Answer 12

Linked List and Bitmap. Bitmap is better because you can easily track continuous sequences of free blocks

Question 13

What does the buffer manager do?

Answer 13

Responsible for bringing pages from disk to main memory.

Question 14

Define the following terms: Buffer Pool, Frame, Pin Count, Dirty Bit

Answer 14

Buffer Pool: the partition of main memory into frames
Frame: A slot in the buffer pool that holds a disk block
Pin Count: Number of users using a frame
Dirty Bit: If the page brought to main memory has been modified or not.

Question 15

For buffer manager, if the page is in the pool, what do you do?

Answer 15

Increment frames pin count and return frame address

Question 16

For buffer manager, what do you do if the page is NOT in the pool.

Answer 16

Find a frame with a pin count of 0.

If dirty bit is on, write whatever is currently on the page to main memory, turn dirty bit off,

Finally, read and load the page into the selected frame, and return frame address.

Question 17

What are the 4 buffer replacement policies?

Answer 17

Least recently used (LRU)
First in First out (FIFO)
Most Recently Used (MRU)
Random

Question 18

What is a DB File?

Answer 18

A collection of pages, containing records from a DB. Provides a way to logical organize records

Question 19

What operations are supported in heap files?

Answer 19

Create/Destroy files
insert/delete/get records with Id
Scan all records

Question 20

What are the 2 Page layouts to store fixed-length records? How do they handle deletions?

Answer 20

Packed: Store the number of records at the very end. When a record is deleted, move the last record into the now free slot.

Bitmap (unpacked): In last row, store bits representing if the slot is free or not (0 = free, 1 = taken). When we delete, set corresponding bit to 0. (see textbook page 328).