C100DBA Sample Questions Answers

mongosh accepts a MongoDB host address in hostname:port form, so mongosh " node-1.cluster1.mycompany.local:27017 " is the valid choice among the commands shown. A canonical URI form such as mongosh " mongodb://node-1.cluster1.mycompany.local:27017 " is also valid, and the connection can alternatively be expressed using --host together with --port. Option A uses an unsupported --hostname switch rather than the documented --host option. Option B invents a --connect flag that is not the standard mongosh interface. Option C constructs an invalid string using an ampersand-style parameter rather than a MongoDB URI or a normal host:port target. Port 27017 is MongoDB ' s default server port, so it could often be omitted if the deployment uses the default, but explicitly including it is valid and removes ambiguity. In authenticated or TLS-enabled environments, the DBA would also supply credentials, authentication database, certificate settings, or a connection string carrying those parameters. For the simple host-and-port requirement in the question, option D is correct.

Study Guide reference/topic:Security, Networking, and Encryption - mongosh connectivity, host/port addressing, and connection options.

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MongoDB equality filters use the form { field: value }. To return the document whose name field contains the exact string " Poppy " , the query therefore uses { name: " Poppy " }, as shown in option D. This shorthand equality syntax is equivalent to explicitly using $eq. Option B uses the correct field but the value is lowercase " poppy " . Normal MongoDB string equality is case-sensitive unless a suitable collation or another case-insensitive technique is deliberately configured, so it does not match the displayed " Poppy " value. Option A uses name.Poppy as a dot-notation path. Dot notation is for accessing a nested field inside an embedded document, but here name stores a scalar string and has no nested Poppy field. Option C searches for a field literally named Poppy, which the sample documents do not contain. This question tests the basic field/value predicate syntax used by find(). The correct command is db.contacts.find({ " name " : " Poppy " }), making option D correct.

Study Guide reference/topic:MongoDB Architecture and Core Operations - find(), equality predicates, string matching, and dot notation.

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MongoDB custom roles are defined in terms of privileges, and each privilege specifies a resource plus one or more allowed actions. For read/query access, find is a valid privilege action. To represent all normal collections in a specified database, MongoDB uses a resource document with the target database and an empty collection name, for example { db: " products " , collection: " " }. Option B therefore combines the correct resource scope with the find action and does not grant write capability. The distractors confuse built-in role names with privilege actions. read, readWrite, and readAnyDatabase are built-in roles or role concepts, not the appropriate action values for the privileges[].actions list shown here. Likewise, a literal " * " collection value is not the documented database-wide resource form for this custom privilege. In practice, an administrator could also assign MongoDB ' s built-in read role rather than creating a custom role if its permissions exactly match the requirement. Given the specific createRole() choices, however, option B is the technically correct construction.

Study Guide reference/topic:Security, Networking, and Encryption - RBAC, custom roles, resources, and privilege actions.

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MongoDB supports direct equality matching against elements contained in an array. When the predicate is { sizes: " M " } and sizes is an array field, a document matches when at least one element of the array equals the scalar value " M " . Document 1 contains only " XS " and " S " , so it does not match. Document 2 contains " M " in [ ' S ' , ' M ' , ' XL ' ], and document 3 contains " M " in [ ' M ' , ' L ' , ' XL ' , ' XXL ' ]; both therefore match. No $elemMatch expression is required for this simple scalar membership test. $elemMatch becomes important when multiple conditions must be satisfied by the same array element, particularly for arrays of embedded documents or compound conditions. This array equality behavior is a core part of MongoDB ' s document query model and allows concise filtering of array-valued fields. The correct result is consequently the t-shirt and vest documents, which corresponds to option D. This same matching behavior applies consistently whenever a scalar predicate targets values stored inside a BSON array field.

Study Guide reference/topic:MongoDB Architecture and Core Operations - querying array fields and equality predicates.

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The query filters only on the sizes field, so the most direct supporting index is a single-field index on sizes. Because sizes contains arrays, MongoDB automatically treats the resulting index as a multikey index and creates index entries derived from the array elements. That allows the query { sizes: " M " } to locate matching documents through the index rather than scanning every document in the collection. Option B indexes item, which is not part of the predicate and therefore does not help this query. Option C contains sizes, but _id is the leading key and the query provides no equality restriction on _id; this prevents efficient use of the later key as a standalone prefix for the query. Option D has the same structural problem because item precedes sizes and is not constrained. MongoDB ' s index-prefix rules make a targeted { sizes: 1 } index the strongest choice here. In a real workload, DBAs should also consider write overhead and whether additional queries can share a compound index before creating redundant indexes. For this single query pattern, option A is optimal.

Study Guide reference/topic:Indexing and Query Optimization - multikey indexes, array fields, index prefixes, and query support.

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MongoDB provides db.grantRolesToUser() specifically for assigning one or more additional roles to an existing user. The method takes the username as its first argument and an array of roles as its second argument, so db.grantRolesToUser( " user1 " , [ " customRole1 " ]) is the correct choice. A role can be supplied as a simple string when it belongs to the current database or as an explicit document such as { role: " customRole1 " , db: " admin " } when the database context must be specified. Option B uses db.createUser(), which is used to create a new user rather than modify the role membership of an account that already exists. Options A and C use method names that are not the documented mongosh interfaces for this operation. Administrators should also distinguish grantRolesToUser() from grantRolesToRole(): the latter makes a user-defined role inherit other roles, whereas the former directly changes a user ' s assigned roles. Least-privilege practice requires granting only roles necessary for the user ' s responsibilities. For the requested update to the existing user, option D is correct.

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

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replaceOne() replaces the matched document ' s content with the replacement document, except that the immutable _id value is preserved when it is not explicitly changed. Ordinary application fields that are omitted from the replacement disappear. The required final document must retain userid, retain first, and change roles to " SuperUser " . Option B supplies all three fields and therefore produces the requested document structure. Option A omits userid, so that ordinary field would be removed from the replacement. Option C omits both userid and first, leaving only roles in addition to the preserved _id. Option D incorrectly uses the update operator $set inside a replacement document. $set belongs with update operations such as updateOne() or updateMany(); a replaceOne() replacement must be a replacement document rather than an update-operator document. This distinction is important for DBAs and application developers because accidental use of a partial replacement can delete fields that were intended to remain. If the goal is only to change one field, updateOne({userid:1}, {$set:{roles: " SuperUser " }}) would normally be safer. Given the choices, B is correct.

Study Guide reference/topic:MongoDB Architecture and Core Operations - replaceOne(), full-document replacement, and update-versus-replacement semantics.

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For a compound index to satisfy a multi-field sort, the indexed fields must occur in the same sequence as the sort specification, and their directions must either match the requested pattern or be the complete reverse of it. The query sorts by { department: 1, salary: -1 }, so option B exactly matches both the key order and the requested directions. MongoDB can scan that index and return the results already ordered, avoiding a blocking in-memory sort. Option A uses { department: 1, salary: 1 }, which does not match the mixed-direction sort and is not its full inverse. Option D puts name before the two sort keys. Because the query has no equality predicate on name, that leading key prevents the later fields from directly providing the requested global sort. Option C is not a sensible index definition for this workload. Separately, the displayed projection mixes inclusion and exclusion (name:1, salary:1, department:0), which MongoDB normally disallows except for _id; that syntax issue should be corrected independently. It does not change the intended index answer for the sort, which is B.

Study Guide reference/topic:Indexing and Query Optimization - compound indexes, sort support, index prefixes, and key direction.

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db.currentOp() is the mongosh helper used to inspect operations currently executing on a MongoDB server. Passing true requests a broad view that includes all in-progress operations as well as additional idle/system entries, so it can be used when the administrator wants to see the complete current-operation picture. The database-command form, db.adminCommand({ currentOp: true }), invokes the corresponding administrative command and is also valid for obtaining in-progress operation information. Option A adds a filter restricting the result to operations whose op field is " command " ; it therefore does not represent all operation types. Option B is not valid currentOp command syntax, and option E uses an all field that is not the documented special form for this helper. In modern MongoDB administration, the $currentOp aggregation stage is generally preferred for richer filtering and aggregation, but the question is testing the traditional helper and command interfaces. Therefore, C and D are the two valid choices among those presented.

Study Guide reference/topic:Performance Monitoring and Tuning - current operations, currentOp, and administrative diagnostics.

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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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The supported mongosh helpers for replica-set membership changes are rs.remove() and rs.add(). rs.remove(hostname) removes the member whose host string matches the supplied host:port, while rs.add() adds a new member using either a host string or a member configuration document that includes a host field. Option C uses those documented methods in the required sequence: remove node 1, remove node 2, then add node 1 back. The names rs.removeNode() and rs.addNode() shown in the other options are not standard MongoDB replica-set helper methods. Membership changes must be performed carefully because modifying voting or data-bearing membership can affect majority calculations, elections, and availability. Administrators normally execute membership changes while connected to the current primary, allow configuration propagation, and verify replica-set health afterward with rs.status() or related diagnostics. If a removed data-bearing node is later re-added, it may need to synchronize depending on how far its data has diverged from the current replica-set history. Among the choices, option C is the only valid command sequence.

Study Guide reference/topic:Cluster Reliability and Data Resilience - replica-set membership, rs.remove(), rs.add(), and topology changes.

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MongoDB can use a compound index to satisfy a multi-field sort when the sort keys appear in the same sequence as the index keys and the requested directions either match the index pattern or are the exact reverse of the entire pattern. The query sorts by { year: 1, rating: -1 }. Option B defines { year: -1, rating: 1 }, which is the complete inverse, so MongoDB can scan that index backward and produce year ascending with rating descending without a blocking in-memory sort. Option A puts title between year and rating; because there is no equality condition fixing title, the index cannot provide a global ordering by { year, rating } across all titles. Options C and D put rating before year, so their primary index ordering does not match the query ' s primary sort key. For multi-field sorts, field sequence is just as important as direction. Therefore B is the strongest index among the presented choices. A forward index { year: 1, rating: -1 } would also be ideal, but it is not offered.

Study Guide reference/topic:Indexing and Query Optimization - compound index sort order, reverse traversal, and index prefixes.

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db.collection.stats() returns statistics for a specific collection, including storage-related values that help a DBA understand that collection ' s disk footprint. Therefore, for a collection named order, db.order.stats() is the relevant command among the choices. The result can include metrics such as logical data size, allocated storage size, document count, index information, and related collection statistics depending on version and storage engine. Option A, db.stats(), reports database-level statistics aggregated across the database rather than isolating the order collection. db.hostInfo(), option C, reports host and operating-system information rather than collection storage consumption. db.serverStatus(), option D, provides broad server-process runtime metrics such as connections, memory, operation counters, replication/storage-engine information, and other health data, but it is not the collection-specific disk-utilization interface requested here. Administrators can also use dedicated helpers such as collection storage-size or total-size methods when they need a more narrowly defined measurement. For a general collection-level statistics query targeting order, however, db.order.stats() is the correct answer, making option B correct.

Study Guide reference/topic:Performance Monitoring and Tuning - collection statistics, storage utilization, db.collection.stats(), and database/server metrics.

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