MongoDB Test 2

Question 1

Which mode does the explain() command operate in by default?

Accepted Answer

queryPlanner

Answer

The `explain()` command in MongoDB provides detailed information about how the database executes a query. By default, it operates in `queryPlanner` mode, which shows the query optimizer's chosen plan without actually executing the query. This mode is useful for understanding index usage and potential performance issues without incurring the overhead of full query execution.

Question 2

The master's oplog uses the ____ storage size measure .

Accepted Answer

MB

Answer

The oplog (operation log) in MongoDB is a special capped collection that records all data-modifying operations on a primary replica set member. Its size is typically configured in megabytes (MB) and is crucial for replication, as secondary members apply operations from the primary's oplog to stay synchronized. A sufficiently large oplog is necessary to prevent secondaries from falling too far behind.

Question 3

The $inc key modifier acts with the _____ data type.

Accepted Answer

numeric

Answer

The `$inc` update operator in MongoDB is specifically designed to increment or decrement the value of a field by a specified amount. This operation is exclusively applicable to numeric data types, such as integers, doubles, or decimals. If `$inc` is applied to a non-numeric field, it will result in an error or unexpected behavior, as it performs arithmetic addition.

Question 4

$push is an array operator that adds a key to an array at the ______.

Accepted Answer

End

Answer

The `$push` operator in MongoDB is used to append a specified value to an array field within a document. When `$push` is applied, the new element is added to the end of the existing array. This makes it a straightforward way to grow an array by adding new items sequentially.

Question 5

Which of the following commands has the potential to lock the database?

Accepted Answer

All of the above

Answer

In earlier versions of MongoDB, many operations, including queries, inserts, and map-reduce jobs, could acquire database-level or collection-level locks. While modern MongoDB with the WiredTiger storage engine offers much finer-grained concurrency (document-level locking), certain administrative commands or very large operations can still escalate to higher-level locks. Therefore, all listed operations have the potential to involve locking mechanisms that could impact concurrent operations.

MongoDB Practice Test

MongoDB Practice Test

MongoDB Test 2