NoSQL - Week 9

Question 1

Can a NoSQL database support SQL?

Answer 1

Yes, some support languages that look a bit like SQL

Question 2

What does NoSQL revisit about relational databases?

Answer 2

• The provision of a declared schema
• Strict transactions

Question 3

What is Data Integrity?

Answer 3

As enforced by a schema, and relied upon by applications

Question 4

What are strict transactional semantics?

Answer 4

That concurrent programs do not lead to inconsistencies

Question 5

What is important in enterprise applications, but may not be prioritised in all cases over scale and flexibility?

Answer 5

Data integrity and strict transactional semantics

Question 6

What needs are NoSQL solutions typically associated with?

Answer 6

Elastic scaling, particularly the ability to grow rapidly for web-scale applications

Simple Operations, in particular accommodating data that tends to be accessed / updated in isolation

Examples: shopping carts, user profiles, blog posts, calendar data, product stock data, customer data, hotel availability, …

The queries don’t refer to all shopping carts or all product data, just to individual chunks

Question 7

What kind of database is useful if you’re expecting 100,000 users but may get 100 million

Answer 7

NoSql

Question 8

What are the 6 abilities that distinguish NoSQL databases?

Answer 8

• To horizontally scale the throughput of simple-operation workloads over many servers.
• To replicate and distribute data (through partitioning) over (thousands of) servers
• To expose a simple call-level interface or protocol
• To offer less strict transactional guarantees
• To use distributed indexes efficiently for replication-rich, elastic provision of data storage
• To cope with variations in the structure of objects stored.

Question 9

What are the three types NoSQL databases are classified into?

Answer 9

Key-Value
Document
Wide Column

Question 10

What is a key-value database?

Answer 10

Access or update a value given a key; the database doesn’t necessarily provide much functionality for the value e.g. queries

(Redis, Oracle NoSQL, Amazon DynamoDB)

Question 11

What is a document database?

Answer 11

Access or update a document using a key; the database will provide functionality for accessing the value (e.g. queries)

Examples: Couchbase, MongoDB

Question 12

What is a wide column database?

Answer 12

Access or update a collection of column families associated with a key (e.g. CustomerID links to contact details, sales details, marketing details)

Examples: Apache Cassandra, HBase

Question 13

What is a Key-Value store?

Answer 13

Associate a key with some data.

It is the responsibility of the application to create and operate on the data.

Question 14

What is the API for a key-value store?

Answer 14

Put(Key,Value)
Get(key)
Delete(key)

Question 15

What is a BLOB?

Answer 15

Binary Large OBject

Question 16

What is a document store?

Answer 16

Associate a key with some data.

Format the data with some recognized format (e.g. JSON)

Question 17

What is the API for a document store?

Answer 17

Put(key, document)
Get(key)
Find(key,filter)
Delete(key)

Question 18

What is a wide column?

Answer 18

Associate a key with some data structured using column families.

API:
- Put(Key, {column family})
- Get(key)
- Delete(key)
- Find(key, filter)
- Update(key, expression)

Question 19

How do you partition data in NoSQL databases vs Relational databases?

Answer 19

Partitioning involves allocating data to different nodes.

In relational databases, partitioning can be vertical (put the data of selected columns together) or horizontal (put collections of rows together)

In NoSQL all the data associated with a key is stored on a single node, so data is horizontally partitioned. This is also known as sharding.

Question 20

Is there a standard language or model for NoSQL?

Answer 20

No

Question 21

Is there a standard language or model for relational databases?

Answer 21

Yes, the SQL standard

Question 22

What is Amazon Dynamo?

Answer 22

A key-value NoSQL database developed to support amazon services, and Amazon hosted applications

It has a different internal model from DynamoDB

Designed for web-scale applications: handling user profiles, shopping carts, game states, leader boards, …

Each service that uses Dynamo has its own instances

Question 23

What are the Stonebreaker-Cattell Rules

Answer 23

R1 Look for shared-nothing scalability

R2 High-level languages are good and need not hurt performance

R3 Plan to carefully leverage main memory databases

R4 High availability and automatic recovery are essential for simple-operation scalability

R5 Online everything

R6 Avoid multi-node operations

R7 Don’t try to build ACID consistency yourself

R8 Look for administrative simplicity

R9 Pay attention to node performance

R10 Open source gives you more control over your future

Question 24

What is a shared-memory design, what is it’s problem?

Answer 24

e.g. multicore, single-node DBMSs over shared primary and secondary memory

Suffer from contention and starve the cores, forcing designers into sharding.

Can only scale to tens of nodes.

Question 25

What is a shared-disk design, what is it’s problem?

Answer 25

(e.g. a multi-core, single node DBMS with private memory per CPU but sharing secondary memory) suffer from complex buffer and lock management needs which limit scalability.

Can only scale to tens of nodes.

Question 26

What is a shared-nothing design, what makes them scalable?

Answer 26

(e.g. each node with its own private and secondary memory)

Are scalable if partitioning is load-balancing (does not lead to hotspots) and if operations touch as few partitions as possible (ideally one)

Can scale to hundreds or thousands of nodes.

Question 27

Does Amazon Dynamo follow R1?

Answer 27

Runs on normal data center nodes, and is shared nothing.

Support get(key), put(key, value), delete (key) operations that act on a single partition.

Scales to hundred or thousands of nodes