GIN index for full-text search in PostgreSQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What does this full-text search query return?

Given a table articles with a content column indexed by a GIN index on to_tsvector('english', content), what rows does this query return?

SELECT id FROM articles WHERE to_tsvector('english', content) @@ to_tsquery('english', 'database & index');

A Rows where the content contains the word 'database' only

B Rows where the content contains either 'database' or 'index'

C Rows where the content contains the exact phrase 'database index'

D Rows where the content contains both words 'database' and 'index' in any order

💡 Hint

The operator '@@' matches documents containing all terms connected by '&' in the tsquery.

The query uses the '@@' operator to match documents where the tsvector contains both 'database' and 'index' terms, regardless of order or adjacency.

🧠 Conceptual

intermediate

Why use a GIN index for full-text search?

Which of the following best explains why a GIN index is preferred for full-text search in PostgreSQL?

A GIN indexes efficiently index composite values like tsvector, allowing fast search for multiple terms

B GIN indexes store data in sorted order for quick range queries

C GIN indexes compress data to save disk space but are slower for search

D GIN indexes are optimized for single-value equality lookups only

💡 Hint

Think about how full-text search needs to find multiple words quickly.

GIN indexes are designed to index composite types like tsvector, which contain multiple lexemes, enabling fast matching of multiple search terms.

📝 Syntax

advanced

Identify the syntax error in this GIN index creation

Which option correctly creates a GIN index on the content column for full-text search in English?

A CREATE INDEX idx_content_gin ON articles (to_tsvector('english', content)) USING GIN;

B CREATE INDEX idx_content_gin ON articles USING GIN (to_tsvector('english', content));

C CREATE INDEX idx_content_gin ON articles USING GIN to_tsvector('english', content);

D CREATE INDEX idx_content_gin ON articles GIN to_tsvector('english', content);

💡 Hint

The syntax requires USING GIN before the indexed expression in parentheses.

The correct syntax is to specify the index method (USING GIN) followed by the indexed expression in parentheses.

❓ optimization

advanced

How to optimize a GIN index for faster updates?

Which option improves update performance on a GIN index used for full-text search?

A Disable autovacuum on the table

B Use a B-tree index instead of GIN for full-text search

C Use the fastupdate = on parameter when creating the GIN index

D Create the index concurrently

💡 Hint

Fastupdate buffers index updates but can slow down queries.

Setting fastupdate = on enables the fast update buffer, which improves update speed at the cost of potentially slower queries.

🔧 Debug

expert

Why does this full-text search query return no rows despite matching content?

Given a GIN index on to_tsvector('english', content), why does this query return zero rows?

SELECT * FROM articles WHERE to_tsvector('simple', content) @@ to_tsquery('simple', 'search');

A The tsvector and tsquery use different configurations, causing no matches

B The GIN index is corrupted and needs reindexing

C The query syntax is invalid and raises an error

D The content column is empty in all rows

💡 Hint

Check if the text search configurations match between index and query.

The index uses 'english' configuration but the query uses 'simple', so lexemes differ and no matches occur.