no sql

Question 1

what are the 4 types of data

Answer 1

structured and unstructured
dynamic and static

Question 2

dynamic

Answer 2

changing frequently

Question 3

static

Answer 3

never changes

Question 4

strcutured

Answer 4

formal predefined
easy to store and process

Question 5

unstructured

Answer 5

e.g. audio, image, music
usually still has internal structural properties

Question 6

sharding data

Answer 6

splitting the data to allow concurrent/parallel access using multiple machines
can simultaneously access each shard

Question 7

in which two ways can we scale databases

Answer 7

vertically and horizontally

Question 8

vertical scaling

Answer 8

upgrading hardware e.g. increasing memory

Question 9

what is the limitaiton of vertical scaling

Answer 9

limited by the amount of cpu ram disk etc that can be configured on a single machine

Question 10

horizontal scaling

Answer 10

adding more machines which requires shading and replication so you can work with them simultaneously

Question 11

what is the limitation of horizontal scaling

Answer 11

read-to-write ratio and communication overhead

Question 12

in which three ways can we benefit form parallelisation

Answer 12

maximise the fraction of the program that can be parallelised
balance the work load and parallel process
minimise the time spent on communication

Question 13

how does the two phase commit protocol work

Answer 13

the coordinator requests cote for commit and the participants either approve or reject
if all participants accept then everything gets committed at the same time

Question 14

what is the issue with two phase commit

Answer 14

hard to find a time where all servers are ready to commit

Question 15

what is the CAP theorem

Answer 15

any distributed database with shared data can have at most 2/3
usually sacrificing consistency

Question 16

what are the three components of cap theorem

Answer 16

consistency; every node always sees the same data at the same time
availability; the system continues operating even if nodes crash or software or hardware is down
partition tolerance; the system works well when distributed

Question 17

what are the BASE properties

Answer 17

basically available; the system guaranteed availability
soft state; system state may change over time
eventual consistency; will eventually become consistent

Question 18

what does it mean for a db to be eventually consistent

Answer 18

if all replicas will gradually become consistent in the absence of updates

Question 19

what makes no sql no sql

Answer 19

no strict schema requirements
no strict adherence to acid properties
consistency is traded in favour of availability

Question 20

document database/store

Answer 20

loosely structured set of key value pairs in documents encapsulate and encode data in some standard formats/encodings
treated as a whole
query languages can help retrieve documents based on their contents
addressed in the db via the unique key

Question 21

in mongo what is the primary key

Answer 21

key; “_id”

Question 22

sorted ordered column-oriented stores

Answer 22

columns are grouped in column families which data is stored in rather than tables
each unit of data is a set of key value pairs identified by row-key

Question 23

graph db

Answer 23

everything is stored as an edge node or attribute
each node and edge can have any number attributes and can be labelled which narrows searches

Question 24

what do document db use instead of an fk

Answer 24

embedded documents and referencing

Question 25

what can be a value in document db

Answer 25

any data type

Question 26

references

Answer 26

including links from one document in another which normalises the db

Question 27

what are some benefits of using referencing

Answer 27

can represent more complex many-to-many relationships
good for large hierarchical datasets

Question 28

what is a negative of using referencing

Answer 28

requires follow up queries to find all the data you need

Question 29

embedded data

Answer 29

having a doc inside another via an array

Question 30

embedded data positive

Answer 30

can get all the data in one call using less queries

Question 31

negative of embedded data

Answer 31

the db isn’t normalised an not all values are atomic

Question 32

data model

Answer 32

displays a set of tables and the relationship between them providing a blueprint so you can identify which data is important and what should be maintained