NoSQL

Question 1

4 points addressed by NoSQL database

Answer 1

non-relational
distributed
open-source
horizontal scalable (we increase the computing power by adding more nodes to the system rather than upgrading an individual node)

Question 2

6 defining characteristics in NoSQL database

Answer 2

• schema-free
• easy replication support
• simple API
• eventually consistent
• BASE principles (not ACID principles)
• huge data amounts

Question 3

6 examples of NoSQL DBs

Answer 3

hadoop/Hbase
cassandra
Amazon SimpleDB
MongoDB
Apache Flink
Google BigTable

Question 4

What does BASE stand for?

Answer 4

Basically Available
Soft state
Eventually Consistent

Question 5

6 Characteristics of BASE database

Answer 5

• weak consistency (stale data ok)
• availability first
• best effort
• approximate answers ok
• aggressive
• simpler and faster

Question 6

What is CAP theorem and how does it apply to NoSQL databases

Answer 6

the idea that it is theoretically impossible to have all 3 of consistency, availability, and partition tolerance

You can only have at most 2 of these. The NoSQL database you choose to use will be mostly based on which of these two characteristics you need the most

Question 7

CAP Theorem: Consistency

Answer 7

all servers in the system will have the same data so anyone using the system will get the same copy regardless of which server answers their request

Question 8

CAP Theorem: Availability

Answer 8

the system will always respond to a request (even if it’s not the latest data or consistent or just a message saying the system isn’t working)

Question 9

CAP Theorem: Partition Tolerance

Answer 9

the system continues to operate as a whole even if individual servers fail or cannot be reached

Question 10

4 NoSQL database types

Answer 10

column store
document store
key-value store
graph database

Question 11

4 basic key-values function calls

Answer 11

• Get(key) - return value
• Put(key, value) - add a key value pair
• Multi-get(key1,..,keyN) return list of values associated with list of keys
• Delete(key) - remove key-value pair from data store

Question 12

2 main issues with Key-value stores

Answer 12

• this model does not provide any traditional database capabilities such as atomicity
• maintaining unique values for keys may become more difficult as the volume of data increases

Question 13

What is a document DB?

Answer 13

expands on key-value store idea but keys refer to “documents” which can contain more complex data

documents hold “semi-structured” data

Question 14

Example of Key-value store

Answer 14

AWS DynamoDB

Question 15

2 examples of document DBs

Answer 15

Couch DB

Mongo DB

Question 16

What is a column store DB?

Answer 16

they store cells in a corresponding column as a continuous disk entry

relational databases store individual rows as continuous disk entries

Question 17

What is the benefit of a column store DB?

Answer 17

accessing a single attribute, searching through a single attribute, and aggregation all only require one disk reference

Question 18

what is a column family?

Answer 18

a logical grouping of columns. The column entries have IDs that allow columns in the column family to be joined to produce a full picture of the data

Question 19

What is a graph DB?

Answer 19

a database based on a graph where data is represented by vertices and the relationships between the data are represented by edges

Question 20

What is the benefit of a graph DB?

Answer 20

it’s ideal for representing complex relationships

Question 21

What is MapReduce?

Answer 21

a programming paradigm that is a technique for indexing and searching large data volumes

Question 22

The two phases of the MapReduce paradigm

Answer 22

the Map phase:
-extracting sets of key-value pairs from underlying data potentially in parallel of different machines

the Reduce phase:
-merge and sort sets of key-value pairs