NoSQLDatabase

Question 1

What are the three key elements that index BigTable’s map?

Answer 1

Row key, Column key, and Timestamp

Question 2

What is a row key in BigTable?

Answer 2

An arbitrary string (10-100 bytes) that uniquely identifies a row

Question 3

What is the purpose of column families in BigTable?

Answer 3

They are basic units of access control and group together columns of the same data type for compression

Question 4

What is the maximum number of column families allowed in a BigTable table?

Answer 4

100

Question 5

How does BigTable divide tables for scalability?

Answer 5

Into tablets (row ranges) of about 100-200 MB

Question 6

What is the format of BigTable’s storage files?

Answer 6

SSTable

Question 7

What are the three levels in BigTable’s location hierarchy?

Answer 7

1. Root tablet in Chubby 2. METADATA tablets 3. SSTable identifiers

Question 8

What two systems does BigTable rely on for core functionality?

Answer 8

Google File System (GFS) for storage and Chubby for distributed lock management

Question 9

Where does BigTable store recently committed updates?

Answer 9

In memory in a sorted buffer called memtable

Question 10

What is BigTable’s main disadvantage?

Answer 10

Cannot handle transactions (no ACID properties), making it unsuitable for banking and e-commerce

Question 11

What are the three key priorities of Amazon DynamoDB?

Answer 11

High availability, scalability, and distributed key-value storage

Question 12

How does DynamoDB achieve incremental scalability?

Answer 12

Through consistent hashing with virtual nodes

Question 13

What is the purpose of virtual nodes in DynamoDB?

Answer 13

They distribute load evenly and handle node failures/additions effectively

Question 14

How many nodes is each data item replicated to in DynamoDB?

Answer 14

N hosts (N is configurable per instance)

Question 15

What is a preference list in DynamoDB?

Answer 15

The list of nodes responsible for storing a particular key

Question 16

What technique does DynamoDB use to detect replica inconsistencies?

Answer 16

Merkle trees (hash trees)

Question 17

What is the hinted handoff technique in DynamoDB?

Answer 17

Temporarily storing data for unavailable replicas on alternate nodes

Question 18

How does DynamoDB track causality in updates?

Answer 18

Using vector clocks with tuples indicating update counts per node

Question 19

What is DynamoDB’s approach to consistency?

Answer 19

Eventual consistency (prioritizes availability over strong consistency)

Question 20

Why was DynamoDB designed with eventual consistency?

Answer 20

To meet the needs of “always-on” applications requiring continuous operation

Question 21

What is the coordinator’s role in DynamoDB?

Answer 21

Responsible for replicating data items that fall within its range

Question 22

How are row keys ordered in BigTable?

Answer 22

Lexicographically

Question 23

What is a locality group in BigTable?

Answer 23

A grouping of column families to enable more efficient reads

Question 24

What type of compression does BigTable support?

Answer 24

Custom two-pass compression system based on Bentley and McIlroy algorithm

Question 25

What is stored in a BigTable value?

Answer 25

An uninterpreted byte string

Question 26

When does BigTable perform authorization checks?

Answer 26

During both read and write operations

Question 27

How does DynamoDB handle conflicting updates?

Answer 27

Through either application-level resolution or system-level resolution (e.g., last write wins)

Question 28

What is the role of Chubby in BigTable authorization?

Answer 28

Stores the list of permitted writers

Question 29

What distinguishes BigTable from traditional databases?

Answer 29

Its non-relational interface and data model

Question 30

Since when has BigTable been operational?

Answer 30

2005