caching Flashcards

1
Q

cold storage

A

data not accessed frequently

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2
Q

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

A

backup data

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3
Q

hard disk

A

rotating and magnetic
usually used for hard storage

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4
Q

solid state drive

A

flash memory with fast access times

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5
Q

what type of memory are disks

A

non volatile

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6
Q

network file system

A

remote server/cloud based storage

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7
Q

what type of memory is ram

A

volatile

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8
Q

how is ram packaged

A

as a chip

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9
Q

what are the 2 types of ram

A

static and dynamic
sram dram

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10
Q

sram

A

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

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11
Q

dram

A

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

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12
Q

registers

A

v small on chip memory

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13
Q

what is the issue with the cpu memory gap

A

cpu speed gets bottlenecked by memory speed

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14
Q

what is the cpu memory gap

A

cpu speed is increasing faster than memory access time

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15
Q

cache

A

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

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16
Q

what is the goal of cache

A

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

17
Q

locality principle

A

accessing a small localised subset of memory

18
Q

temporal locality

A

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

19
Q

spacial locality

A

data near recently accessed addresses likely to be accessed

20
Q

how do we exploit temporal memory

A

keep the recently accessed data in the cache

21
Q

how do we exploit spacial memory

A

prefetch data before its requested

22
Q

how do we calculate the cache hit rate

A

number of hits/ number of lookups

23
Q

row major order

A

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

24
Q

stride k reference pattern

A

k = the unit of jumps between memory addresses being accessed

25
how does the cache work
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
26
what are 3 examples of a cache eviction policy
belady's algorithm least recently used first in first out
27
belady's algorithm cache eviction policy
evicts the block that wont be used for the longest time
28
what is the issue with belady's algorithm
you will need to know future lookups therefore its not always practical
29
least recently used cache eviction policy
evicts the block that hasnt been used in the longest time
30
how can we implement the least recently used cache eviction policy
a doubly linked list maintains the block from most to least recently used a hash table implemented in a dictionary is used for lookups
31
fifo cache eviction policy
the cache implements a queue
32
what is the issue with fifo cache eviction policy
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
33
server side caching
stores data temporarily on the server to speed up future access to that data usually as a db query result
34
what are some benefits of server side caching
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
35
how do content distribution networks work
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
36
what does an edge/ cdn server do
replicated the content providers data