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| Certification Vendor: | MongoDB |
|---|---|
| Exam Name: | MongoDB Certified DBA Associate Exam (Based on MongoDB 4.4) |
| Exam Number: | C100DBA |
| Exam Duration: | 90 minutes |
| Exam Price: | $150 USD |
| Certificate Validity Period: | Not officially specified |
| Related Certifications: | MongoDB Certified Developer Associate |
| Available Languages: | English |
| Exam Format: | Multiple Response, Multiple Choice |
| Real Exam Qty: | 60-66 |
| Passing Score: | 490/600 |
| Sample Questions: | MongoDB C100DBA Sample Questions |
| Exam Way: | Online proctored or authorized testing center |
| Pre Condition: | Recommended knowledge of fundamental database concepts, basic system administration, and basic JavaScript. No mandatory prerequisite exam. |
| Official Syllabus URL: | https://learn.mongodb.com/pages/mongodb-associate-database-administrator-exam |
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MongoDB C100DBA Exam is designed to validate the skills and knowledge of individuals who want to become certified MongoDB database administrators. C100DBA exam is based on MongoDB 4.4, the latest version of the popular NoSQL database. Candidates are expected to have a deep understanding of MongoDB's architecture, installation and configuration, data modeling, security, and performance tuning.
NEW QUESTION # 111
A MongoDB administrator is managing a database for a hospital system.
The patients collection contains:
- Carlos Martinez, diagnosis Hypertension, room 203
- Maria Lopez, diagnosis Hypertension, room 207
- Juan Perez, diagnosis Arrhythmia, room 207
The administrator runs:
db.patients.updateMany(
{ diagnosis: " Hypertension " },
{ $set: { room: 207 } }
)
What output should the administrator expect?
Answer: B
Explanation:
updateMany() distinguishes between documents that match the filter and documents whose stored data actually changes. The filter { diagnosis: " Hypertension " } matches Carlos Martinez and Maria Lopez, so matchedCount is 2. Carlos currently has room: 203, and $set: { room: 207 } changes his document, contributing one to modifiedCount. Maria already has room: 207. She still satisfies the filter and therefore counts as a match, but setting a field to the value it already contains does not produce a material modification, so she does not increment modifiedCount. Juan Perez has diagnosis Arrhythmia, so he is neither matched nor modified. The resulting acknowledged operation therefore reports matchedCount: 2 and modifiedCount: 1, corresponding to option D. This distinction is essential when validating whether an update actually changed stored values rather than merely identifying matching records. This distinction is operationally important: a large difference between matched and modified counts can indicate that many matching documents already contained the requested state, not that the update failed. DBAs should use both counters when validating bulk- update behavior.
Study Guide reference/topic:MongoDB Architecture and Core Operations - updateMany(), $set, matchedCount, and modifiedCount.
NEW QUESTION # 112
Which TWO commands can be used to check for all active operations on the current node?
Answer: B,E
Explanation:
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.
NEW QUESTION # 113
Given the following query:
db.load.find({
_id: { $lte: 1000 },
rnd: 1234,
date: { $gte: ISODate( " 2023-01-01 " ) }
}).sort({ date: -1 })
In a compound index that best supports this query, what field should be first field?
Answer: A
Explanation:
The rnd field should lead the compound index because it is the query ' s equality predicate. MongoDB ' s common compound-index design rule is Equality, Sort, Range (ESR): fields tested for exact equality are typically placed first, followed by fields used for sorting and then range predicates, subject to workload- specific selectivity considerations. Here, rnd: 1234 is an equality condition. _id: { $lte: 1000 } is a range condition, and date: { $gte: ... } is also a range condition while the query additionally sorts on date. Leading with rnd sharply narrows the index region that must be scanned before MongoDB handles the sort/range dimensions. Starting with _id or date would place a range-oriented key ahead of the exact-match predicate and generally reduce the efficiency of index bounds for this query shape. The complete optimal key pattern may depend on whether avoiding the sort or maximizing range selectivity matters most, but the question asks only for the first field. Under ESR guidance, that first field is rnd, so option B is correct.
Study Guide reference/topic:Indexing and Query Optimization - compound indexes, selectivity, and the Equality-Sort-Range guideline.
NEW QUESTION # 114
What is one purpose of a hidden index?
Answer: A
Explanation:
A hidden index remains physically present and continues to be maintained as documents are inserted, updated, or deleted, but the query planner does not consider that index when choosing normal execution plans. This makes hidden indexes especially useful for safely testing whether an index can be removed. An administrator can hide the index and observe production query behavior as though the index were absent. If performance or plan quality degrades, the index can be unhidden immediately without rebuilding it because MongoDB has continued to maintain it in the background. Option A is incorrect because a hidden index is still an index and is not simply removed from index statistics. Option B is also incorrect; hiding an index can actually force collection scans or alternative plans if that index was previously important. Option D misunderstands the feature entirely: hiding an index has no effect on document visibility. Hidden indexes are therefore a risk-reduction mechanism for index lifecycle management, especially before dropping an index in a production environment. Option C accurately states that purpose.
Study Guide reference/topic:Indexing and Query Optimization - hidden indexes, query planner behavior, and safe index-removal testing.
NEW QUESTION # 115
In a replica set with a primary and two secondaries, what should the write concern be set to so only a single node is required to acknowledge a write operation before it is deemed successful?
Answer: C
Explanation:
MongoDB write concern defines the level of acknowledgment requested for a write. Setting the numeric value w: 1 means that a write is considered acknowledged after the primary has accepted it; no secondary acknowledgment is required. In a replica set with one primary and two secondaries, those secondaries can replicate the operation asynchronously after the client has already received success. That configuration is represented by { writeConcern: { w: 1 } }, making option D correct. The numeric type matters: w can be specified as an integer count or certain strings such as " majority " , but the string " 1 " is not the intended numeric node count shown by the question. Options B and C also omit the w field structure expected inside a write concern document. The durability trade-off is important: a w:1 write can be acknowledged before any secondary has replicated it, so a sudden primary failure before replication may result in that write being rolled back after failover. If the workload requires stronger durability, w: " majority " is commonly used. For exactly one acknowledging node, however, the correct setting is D.
Study Guide reference/topic:Cluster Reliability and Data Resilience - write concern, w acknowledgments, replica-set durability, and rollback risk.
NEW QUESTION # 116
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