Percolate queries (reverse search) in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this percolate query count?

Given an index with percolator queries registered, what will be the count of matching queries for the document below?

{"query": {"match": {"message": "quick brown fox"}}}

Assume the percolator index has two queries: one matching "quick" and another matching "lazy".

Elasticsearch

{
  "query": {
    "percolate": {
      "field": "query",
      "document": {
        "message": "quick brown fox"
      }
    }
  }
}

A 2

B 1

C 0

D Query syntax error

💡 Hint

Think about which registered queries match the document text.

The document contains the word "quick" which matches one registered query. The other query matches "lazy" which is not in the document, so only one query matches.

🧠 Conceptual

intermediate

Which field type is required to store percolator queries?

In Elasticsearch, to register queries for percolation, which field type must be used in the mapping?

A "text"

B "keyword"

C "percolator"

D "nested"

💡 Hint

It's a special field type designed for storing queries.

The "percolator" field type is specifically designed to store queries for reverse search in Elasticsearch.

🔧 Debug

advanced

Why does this percolate query fail with a parsing error?

Consider this percolate query:

{
  "query": {
    "percolate": {
      "field": "query",
      "document": {
        "message": "fox jumps"
      },
      "index": "my_index"
    }
  }
}

It returns a parsing error. What is the cause?

A The "field" value must be the name of a "percolator" field, not "query"

B The "document" field must be replaced with "documents" array

C The "index" parameter is not allowed inside the percolate query

D The "message" field is missing from the mapping

💡 Hint

Check the field name used for percolate queries in the mapping.

The "field" parameter must point to the field of type "percolator" in the index mapping. Using "query" if that is not the percolator field causes parsing errors.

📝 Syntax

advanced

Which option correctly registers a percolator query in Elasticsearch?

You want to register a percolator query that matches documents containing "error" in the "message" field. Which JSON is correct?

A { "query": { "match": { "message": "error" } } }

B { "query": { "percolate": { "field": "query", "document": { "message": "error" } } } }

C { "query": { "match": { "query": "error" } } }

D { "query": { "term": { "message": "error" } } }

💡 Hint

Registering a percolator query requires a valid query JSON, not a percolate query.

When registering a percolator query, you store a normal query (like match) inside the percolator field. Option A is the correct query to store.

🚀 Application

expert

How many queries match this document using percolate query?

Assume you have registered these percolator queries:

1. Match "error" in "message"
2. Match "warning" in "message"
3. Match phrase "disk failure" in "message"

What is the number of matching queries for this document?

{"message": "disk failure error detected"}

A 0

B 3

C 1

D 2

💡 Hint

Check which registered queries match the document text.

The document contains "disk failure" phrase and the word "error". So queries 1 and 3 match, but not query 2.