MEAN MongoDB Advanced Operations 5

Question 1

In MongoDB, what is a 'covered query'?

Accepted Answer

A query satisfied entirely by an index without scanning the collection documents

Answer

A covered query is one where all fields in the query predicate and projection are part of the same index, so MongoDB never needs to access the actual documents.

Question 2

Which MongoDB aggregation stage is used to add new fields to documents or overwrite existing fields without replacing the entire document?

Accepted Answer

Both $addFields and $set

Answer

Both $addFields and $set (its alias introduced in MongoDB 4.2) add or overwrite fields while preserving all other existing fields in the document.

Question 3

What is the default behavior of MongoDB's WiredTiger storage engine regarding data compression?

Accepted Answer

Uses snappy compression for collections and zlib for indexes by default

Answer

WiredTiger defaults to snappy compression for collection data and prefix compression for indexes, balancing CPU overhead and storage savings.

Question 4

In a MongoDB sharded cluster, what is a 'jumbo chunk'?

Accepted Answer

A chunk that exceeds the configured chunk size and cannot be split because all documents share the same shard key value

Answer

Jumbo chunks occur when a range of shard key values contains too many documents that cannot be further divided, often causing hotspots.

Question 5

What does the MongoDB explain() 'executionStats' verbosity mode return that the 'queryPlanner' mode does not?

Accepted Answer

Actual runtime statistics including documents examined and execution time

Answer

'executionStats' runs the query and returns real performance metrics like nReturned, totalDocsExamined, and executionTimeMillis.

MEAN - Stack Development Practice Test

MEAN - Stack Development Practice Test

MEAN MongoDB Advanced Operations 5