caching

Question 1

cold storage

Answer 1

data not accessed frequently

Question 2

what is an example of something that would be stored on cold storage

Answer 2

backup data

Question 3

hard disk

Answer 3

rotating and magnetic
usually used for hard storage

Question 4

solid state drive

Answer 4

flash memory with fast access times

Question 5

what type of memory are disks

Answer 5

non volatile

Question 6

network file system

Answer 6

remote server/cloud based storage

Question 7

what type of memory is ram

Answer 7

volatile

Question 8

how is ram packaged

Answer 8

as a chip

Question 9

what are the 2 types of ram

Answer 9

static and dynamic
sram dram

Question 10

sram

Answer 10

shorter access time
has 6x more transistors to store bits than dram making it more expensive

Question 11

dram

Answer 11

usually used as memory on personal devices as its cheaper than sram

Question 12

registers

Answer 12

v small on chip memory

Question 13

what is the issue with the cpu memory gap

Answer 13

cpu speed gets bottlenecked by memory speed

Question 14

what is the cpu memory gap

Answer 14

cpu speed is increasing faster than memory access time

Question 15

cache

Answer 15

a smaller faster storage device that acts as a staging area for a subset of data in a larger slower device

Question 16

what is the goal of cache

Answer 16

achieve access speeds of the fastest memory whilst paying the cost of the cheapest

Question 17

locality principle

Answer 17

accessing a small localised subset of memory

Question 18

temporal locality

Answer 18

recently accessed data likely to be accessed again in the near future

Question 19

spacial locality

Answer 19

data near recently accessed addresses likely to be accessed

Question 20

how do we exploit temporal memory

Answer 20

keep the recently accessed data in the cache

Question 21

how do we exploit spacial memory

Answer 21

prefetch data before its requested

Question 22

how do we calculate the cache hit rate

Answer 22

number of hits/ number of lookups

Question 23

row major order

Answer 23

elements in the same row of an array are stored next to eachother in memory

Question 24

stride k reference pattern

Answer 24

k = the unit of jumps between memory addresses being accessed

Question 25

how does the cache work

Answer 25

read the cache to look for the block
if its already there then you get a cache hit
if not then you get a cache miss
if its a miss then you fetch it from slower memory
if the cache isnt full then add the block to it
if its full then you need to evict an existing block based on the cache eviction policy

Question 26

what are 3 examples of a cache eviction policy

Answer 26

belady’s algorithm
least recently used
first in first out

Question 27

belady’s algorithm cache eviction policy

Answer 27

evicts the block that wont be used for the longest time

Question 28

what is the issue with belady’s algorithm

Answer 28

you will need to know future lookups therefore its not always practical

Question 29

least recently used cache eviction policy

Answer 29

evicts the block that hasnt been used in the longest time

Question 30

how can we implement the least recently used cache eviction policy

Answer 30

a doubly linked list maintains the block from most to least recently used
a hash table implemented in a dictionary is used for lookups

Question 31

fifo cache eviction policy

Answer 31

the cache implements a queue

Question 32

what is the issue with fifo cache eviction policy

Answer 32

belady’s anomaly; increasing the cache size leads to a higher number of misses
you may be removing the entry that is most frequently used

Question 33

server side caching

Answer 33

stores data temporarily on the server to speed up future access to that data
usually as a db query result

Question 34

what are some benefits of server side caching

Answer 34

allows near real time communication by providing low latency
manages popular shared content
massive scalability
allows redundancy and replication ensuring data availability and fault tolerance

Question 35

how do content distribution networks work

Answer 35

a client requests a url for a video
the client resolves the domain name from the local dns
the dns returns the domain name to the client who then passes it to the cnd to get the content
the edge serve has cached copies of static content originally hosted on the origin server
when it is first requested it is fetched from the og server and is then cached for resuse

Question 36

what does an edge/ cdn server do

Answer 36

replicated the content providers data