Free DP-420 sample questions

Correct answer: The merge stored procedure is not registered in the European region's Cosmos DB instance.

When using a custom conflict resolution policy with a merge stored procedure, the stored procedure must be created in each region where writes can occur. If the stored procedure is only registered in the North America region, conflicts originating from writes in Europe will fail to be resolved correctly, leading to data loss. The conflict resolution mechanism will fall back to a default behavior which might not align with the intended merge logic.

Correct answers: Store the `_lsn` (Log Sequence Number) of the last successfully processed event from the change feed and check against it before processing a new event.; Design the materialized view updates as upsert operations based on a unique identifier from the source event.

The `_lsn` property is a unique, monotonically increasing number for each change. By tracking the last successfully processed `_lsn` for each partition in your destination (or a separate state store), your function can check if an incoming event's `_lsn` has already been processed, thus achieving idempotency.

Making the write operations to the materialized views idempotent is crucial. Using an upsert (`CreateItemAsync` or `ReplaceItemAsync` logic) ensures that if an event is processed twice, the second operation simply overwrites the existing data with the same information, rather than creating a duplicate entry.

Correct answer: { "indexingMode": "consistent", "automatic": true, "includedPaths": [ { "path": "/*" } ], "excludedPaths": [ { "path": "/sessionTrace/*" } ] }

This policy correctly uses the default behavior of indexing everything (`includedPaths` with `/*`) and then specifically carves out an exception. The `excludedPaths` array with the path `/sessionTrace/*` tells Cosmos DB to not index the `sessionTrace` property or any of its sub-properties. The `*` is a wildcard that matches any element beyond the `sessionTrace` property.

Correct answer: `properties.locations`

The `properties.locations` property in an ARM template for a Cosmos DB account is an array of location objects. Each object specifies a `locationName` and a `failoverPriority`. The region with `failoverPriority: 0` is the primary write region, and subsequent regions are assigned priorities of 1, 2, and so on, for the automatic failover order.

Correct answer: True

Transactional batch operations in Azure Cosmos DB for NoSQL are scoped to a single logical partition. This is because they are executed as a single transaction on the database engine replica set that hosts the logical partition. This constraint ensures ACID properties for the operations within the batch. If you attempt to include operations for documents in different logical partitions, the entire batch operation will fail.

Correct answer: Hot Partition; choose a new partition key with higher cardinality and more even request distribution.

This scenario describes a classic 'hot partition' problem. A single physical partition is receiving a disproportionate amount of requests, causing it to hit the maximum throughput limit for a single partition (10,000 RU/s), while the overall container throughput is underutilized. The fundamental solution is to change the partition key to one that distributes requests more evenly across all logical and physical partitions, such as using a synthetic key or a key with higher cardinality.

Correct answer: Migrate the account from periodic to continuous backup mode and set the retention to 15 days.

The requirement for granular, second-level point-in-time restore (PITR) can only be met by continuous backup mode. Periodic backup creates discrete snapshots at set intervals (e.g., every 4 hours). Continuous backup, on the other hand, constantly records changes, allowing for restoration to any point in time within the retention period (up to 30 days). The first step is to migrate the account's backup policy, which can be done via the Azure Portal, CLI, or ARM templates.

Correct answer: Cosmos DB Operator

The 'Cosmos DB Operator' role is specifically designed for this scenario. It grants permissions to manage Azure Cosmos DB resources (accounts, databases, containers) but does not grant access to the data itself or the ability to use the Data Explorer. This effectively separates control plane management from data plane access, adhering to the principle of least privilege.

Correct answer: It will be a cross-partition query because the full synthetic partition key is not provided in the filter.

For a query to be a single-partition query, the `WHERE` clause must include a filter that specifies the exact value of the partition key. In this case, the partition key is `deviceId` combined with the month and year. The query only filters on `deviceId` and `timestamp`. Since the full partition key value (e.g., 'DEVICE123-2024-08') cannot be derived from the query filters, Cosmos DB must execute it as a cross-partition query, scanning all partitions that could potentially contain data for 'DEVICE123'.

Correct answers: It prevents socket exhaustion by reusing TCP connections across multiple requests.; It caches the database account's address routing table, avoiding repeated metadata lookups.; It allows for efficient connection management, especially when using Direct connectivity mode.

Creating a new `CosmosClient` for each request can lead to creating new TCP connections, which can exhaust the available sockets on the client machine, leading to connectivity errors.

The `CosmosClient` instance performs initial metadata requests to get the routing table for partitions. Reusing the client allows this information to be cached, significantly reducing the latency of subsequent requests.

The `CosmosClient` is responsible for managing the underlying connections. A singleton pattern ensures this management is efficient and stable over the lifetime of the application, which is particularly important for the more complex connection pooling used in Direct mode.