MongoDB Updated C100DBA Exam Questions and Answers by peyton

The documented mongosh helper is db.revokeRolesFromUser(), and its second argument is an array of roles to revoke. MongoDB permits each role in that array to be expressed either as an explicit document { role: < roleName > , db: < database > } or, when the role belongs to the database in which the command is run, as a simple role-name string. Option C uses the explicit role-document form and is therefore valid for a role named specialRole defined in myDB. Option E uses the shorthand string form and is valid when specialRole is in the current database context. Option A reverses the required document structure and does not supply the mandatory role and db keys. Options B and D use a singular helper, db.revokeRoleFromUser(), which is not the documented MongoDB method. The plural method name reflects that multiple roles can be revoked in a single operation. Administrators should also remember that revoking a directly assigned role does not necessarily remove privileges inherited through other roles. Among the choices, C and E are the syntactically valid revocation forms.

Study Guide reference/topic:Security, Networking, and Encryption - RBAC, user administration, and revokeRolesFromUser().

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In MongoDB explain output, a COLLSCAN stage means the winning plan is scanning documents in the collection rather than traversing a suitable index. This is the clearest indicator that the query is not being serviced by a normal index scan for the relevant predicate. By contrast, IXSCAN explicitly indicates an index scan and typically includes details such as the index key pattern, direction, and bounds. A FETCH stage represents retrieval of full documents, often after an index has already identified candidate record locations; its presence does not imply that no index was used. GROUP relates to grouping behavior and is not the stage used to identify missing index support. A collection scan is not automatically wrong: for tiny collections or queries that return most documents, it can be efficient. However, on large collections with selective predicates, repeated COLLSCAN plans are a strong signal that the DBA should evaluate indexing. Administrators should compare totalDocsExamined, totalKeysExamined, execution time, and the winning/rejected plans before deciding to add an index. For the terminology tested by the question, COLLSCAN is the correct stage, so C is correct.

Study Guide reference/topic:Indexing and Query Optimization - explain plans, COLLSCAN, IXSCAN, and missing index diagnostics.

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