ElasticSearch ElasticSearch 3 — Questions and Answers
Question 1: Which Elasticsearch component is responsible for routing documents to the correct primary shard?
- The coordinating node using a hash of the document ID (Correct answer)
- The master node based on cluster state
- The data node with the lowest disk usage
- The ingest node after pipeline processing
Correct answer: The coordinating node using a hash of the document ID
By default, Elasticsearch routes documents to shards using a hash of the document ID modulo the number of primary shards.
Question 2: What is a 'near real-time' (NRT) search in Elasticsearch?
- Search that returns results within 1 millisecond
- Search that becomes available within ~1 second after indexing due to refresh intervals (Correct answer)
- Search performed only on primary shards
- Search using caching to avoid re-scanning indices
Correct answer: Search that becomes available within ~1 second after indexing due to refresh intervals
Elasticsearch is near real-time because indexed documents become searchable only after a refresh (default every 1 second), not immediately.
Question 3: In Elasticsearch, what does the `must_not` clause in a bool query do?
- Requires all listed queries to match
- Boosts scores for matching documents
- Excludes documents that match any of the listed queries (Correct answer)
- Makes matching optional but score-contributing
Correct answer: Excludes documents that match any of the listed queries
The must_not clause excludes documents that match any of its queries, and matching documents contribute a score of 0.
Question 4: What is the role of a 'master-eligible' node in an Elasticsearch cluster?
- To handle all search requests from clients
- To store all primary and replica shards
- To participate in master election and manage cluster state (Correct answer)
- To preprocess documents before indexing
Correct answer: To participate in master election and manage cluster state
Master-eligible nodes can be elected as the cluster master, which manages cluster-wide settings, shard allocation, and node membership.
Question 5: Which Elasticsearch API is used to retrieve the mapping of an index?
- GET /<index>/_settings
- GET /<index>/_mapping (Correct answer)
- GET /<index>/_schema
- GET /<index>/_fields
Correct answer: GET /<index>/_mapping
The GET `/<index>/_mapping` API returns the field mappings defined for the specified index.
Question 6: What happens when you send a document to Elasticsearch with an ID that already exists using a PUT request to `/<index>/_doc/<id>`?
- The request is rejected with a 409 conflict error
- The existing document is deleted and replaced with the new one (Correct answer)
- The new fields are merged into the existing document
- The operation is queued until the existing document is refreshed
Correct answer: The existing document is deleted and replaced with the new one
A PUT to `/<index>/_doc/<id>` performs an index operation that fully replaces the existing document, incrementing its version number.
Question 7: Which analysis component in Elasticsearch is responsible for breaking text into individual tokens?
- Character filter
- Token filter
- Tokenizer (Correct answer)
- Normalizer
Correct answer: Tokenizer
The tokenizer receives a stream of characters and breaks it into individual tokens (usually words), which are then passed to token filters.
ElasticSearch ElasticSearch 3
Which Elasticsearch component is responsible for routing documents to the correct primary shard?