Basics

Question 1

Document

Answer 1

JSON File Converted into a ES Document

Question 2

Index

Answer 2

Collection of Documents

Question 3

Shard

Answer 3

Index is a collection of shards. Shards are distributed over nodes

Question 4

Node

Answer 4

An instance of elasticsearch. Can have umltiple nodes running on a physical machine

Question 5

Primary Shard & Replica Shard

Answer 5

Primary Shard is the first shard. Replica Shard is replica of the primary shard

Question 6

Cluster

Answer 6

Collection of index, developed for specific purpose, like eComm Seaarch, APM. Cross Cluster Searches are possible

Question 7

Routing Formula and No of Replicas

Answer 7

shard_number = hash(documentid) + number of replicas
Number of replicas of index cannot be changed as it would affect the routing formula

Question 8

Add documents

Answer 8

POST /index_name/_doc/
{
“field1”: “value1”,
“field2”: “value2”
}

Question 9

Delete documents

Answer 9

DELETE /index_name/_doc/document_id

Question 10

Update documents

Answer 10

POST /index_name/_doc/document_id/_update
{
“doc”: {
“field1”: “new_value”
}
}

Question 11

Create Index

Answer 11

PUT /index_name
{
“settings”: {
“number_of_shards”: 1,
“number_of_replicas”: 1
},
“mappings”: {
“properties”: {
“field1”: { “type”: “text” },
“field2”: { “type”: “keyword” }
}
}
}

Question 12

DELETE index

Answer 12

DELETE /index_name

Question 13

Optimistic Concurrency Control

Answer 13

To ensure an older version of a document doesn’t overwrite a newer version, every operation performed to a document is assigned a sequence number by the primary shard that coordinates that change. The sequence number is increased with each operation and thus newer operations are guaranteed to have a higher sequence number than older operations.

As an application developer you need to pass the primary term and sequence number during the update, to make sure that you are not updating an older copy of the document

First do a GET and get the sample fields in the response. Then do a POST to update the contents

PUT products/_doc/1567?if_seq_no=362&if_primary_term=2
{
“product”: “r2d2”,
“details”: “A resourceful astromech droid”,
“tags”: [ “droid” ]
}

Question 14

Inverted Index

Answer 14

Mapping between keyword to document number
Ex
Document 1 :
Space : The final frontier. These are the voyages..

Document 2 :
He’s bad, he’s the number one. He’s the space cowboy with the laser gun!

space: 1,2
the: 1,2
final: 1
frontier: 1
he: 2
bad: 2

Question 15

TF-IDF

Answer 15

Term Frequence * Inverse Document Frequency

Question 16

Term Frequency

Answer 16

is how often a term appears in a given document.

Question 17

Document Frequency

Answer 17

is how often a term appears in all documents

Important point.
The word ‘the’ may have a high document frequency

The word ‘space’ may have a low document frequency

Question 18

Term Frequency/ Document Frequency or Relevancy

Answer 18

Measures the relevance of a term in a document