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| Section | Objectives |
|---|---|
| Topic 1: Data Modeling | - Schema design principles - Relationships in MongoDB - Embedding vs referencing |
| Topic 2: Indexing and Performance Tuning | - Query performance optimization - Index types and usage - Explain plans and diagnostics |
| Topic 3: MongoDB CRUD Operations | - Insert, update, and delete operations - Working with documents and BSON types - Querying and filtering documents |
| Topic 4: Security | - Encryption at rest and in transit - Role-based access control (RBAC) - Authentication and authorization |
| Topic 5: Replication and High Availability | - Read/write concerns - Failover and elections - Replica set architecture |
| Topic 6: Sharding and Scalability | - Sharded cluster architecture - Balancing and scaling operations - Shard keys and distribution strategy |
| Topic 7: Aggregation Framework | - Aggregation pipeline stages - Data transformation and grouping - Aggregation operators |
| Topic 8: Backup, Restore, and Operations | - Monitoring and maintenance - Backup strategies and tools - Restore procedures |
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問題 #114
A collection named scores includes:
[
{ _id: 1, home_score: 6, away_score: [ 5, 7 ] },
{ _id: 2, home_score: [ 8, 6 ], away_score: 9 },
{ _id: 3, home_score: [ 5, 8 ], away_score: [ 9, 6 ] },
{ _id: 4, home_score: 5, away_score: 10 }
]
Given the following index:
db.scores.createIndex( { home_score: 1, away_score: 1 } )
What document will cause the index to fail?
答案：A
解題說明：
The proposed index is a compound index across home_score and away_score. MongoDB supports compound multikey indexes, but it imposes an important restriction: for any one indexed document, no more than one field covered by the compound index may contain an array. Document 1 is valid because only away_score is an array. Document 2 is also valid because only home_score is an array. Document 4 contains scalar values for both fields. Document 3 contains arrays in both indexed fields: home_score: [5,8] and away_score: [9,6] .
Indexing that document would require a compound multikey index to expand two independent array dimensions, which MongoDB prohibits. Therefore document 3 prevents the compound index from being valid. The restriction is important because a single multikey field already creates multiple index keys per document; allowing multiple independently array-valued keys in the same compound index would create ambiguous and potentially combinatorial key combinations. DBAs designing indexes over document schemas with arrays must understand these multikey constraints before building compound indexes. The failing document is _id:3, making option D correct.
Study Guide reference/topic:Indexing and Query Optimization - multikey indexes, compound multikey restrictions, and array-valued fields.
問題 #115
Below is a sample document of " orders " collection
答案：
解題說明：
$project
問題 #116
What " stage " indicates that no indexes were available for a query pattern?
答案：D
解題說明：
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.
問題 #117
What mongosh command connects to node-1.cluster1.mycompany.local on port 27017?
答案：B
解題說明：
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.
問題 #118
In a replica set, a_________number of members ensures that the replica set is always able to select a primary.
答案：C
問題 #119
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順便提一下，可以從雲存儲中下載Testpdf C100DBA考試題庫的完整版：https://drive.google.com/open?id=1i8AwzeRyLD4ZOJu28Xr3-T5AY2h1z6gB