Range-based sharding in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable sharding on the database named 'sales'.

MongoDB

sh.enableSharding("[1]")

Drag options to blanks, or click blank then click option'

Ausers

Binventory

Csales

Dorders

Attempts:

3 left

💡 Hint

Common Mistakes

Using a collection name instead of the database name.

Misspelling the database name.

The enableSharding command activates sharding on the specified database. Here, the database is named 'sales'.

2fill in blank

medium

Complete the code to shard the 'orders' collection on the 'orderDate' field.

MongoDB

sh.shardCollection("sales.[1]", { orderDate: 1 })

Drag options to blanks, or click blank then click option'

Acustomers

Borders

Cproducts

Dinventory

Attempts:

3 left

💡 Hint

Common Mistakes

Using the database name instead of the collection name.

Forgetting to specify the shard key field.

The shardCollection command shards the specified collection. Here, the collection is 'orders' in the 'sales' database.

3fill in blank

hard

Fix the error in the code to create a range shard on the 'age' field for the 'users' collection.

MongoDB

sh.splitAt("users.users", { age: [1] })

Drag options to blanks, or click blank then click option'

A25

B"25"

C{25}

D[25]

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around the number, making it a string.

Using brackets or braces which are invalid here.

The splitAt command requires the shard key value as a number, not as a string or object. So, use 25 without quotes or brackets.

4fill in blank

hard

Fill both blanks to split the 'orders' collection at the specified range and move the chunk to shard02.

MongoDB

sh.splitAt("sales.orders", { [1]: 1000 })
sh.moveChunk("sales.orders", { [2]: 1000 }, "shard02")

Drag options to blanks, or click blank then click option'

AorderId

BcustomerId

CorderDate

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using different fields for splitting and moving chunks.

Using a field that is not the shard key.

Both splitAt and moveChunk commands use the shard key field, which is 'orderId' here, to specify the range and chunk location.

5fill in blank

hard

Fill all three blanks to create a range-based shard key on 'price', split at 500, and move the chunk to 'shard01'.

MongoDB

sh.shardCollection("store.products", { [1]: 1 })
sh.splitAt("store.products", { [2]: [3] })
sh.moveChunk("store.products", { [2]: [3] }, "shard01")

Drag options to blanks, or click blank then click option'

Aprice

C500

D1000

Attempts:

3 left

💡 Hint

Common Mistakes

Using different fields for shard key and split/move commands.

Using the wrong split value.

The shard key is 'price'. The split and move chunk commands use the same field 'price' and split at the value 500.

Practice

1. What is the main idea behind range-based sharding in MongoDB?

easy

A. Data is randomly distributed across shards.

B. Data is split into ranges based on shard key values.

C. Data is duplicated on all shards for backup.

D. Data is stored only on a single shard.

Solution

1. Step 1: Understand range-based sharding concept

   Range-based sharding divides data into continuous ranges based on shard key values.

2. Step 2: Compare with other options

   Random distribution or duplication are not characteristics of range-based sharding.

3. Final Answer:

   Data is split into ranges based on shard key values. -> Option B

4. Quick Check:

   Range-based sharding = Data split by ranges [OK]

Hint: Remember: range-based means splitting by value ranges [OK]

Common Mistakes:

• Confusing range-based with hash-based sharding
• Thinking data is duplicated on all shards
• Assuming data is randomly distributed

2. Which of the following is the correct way to enable range-based sharding on a collection in MongoDB?

easy

A. sh.shardRangeCollection("db.collection", { "field": 1 })

B. sh.enableRangeSharding("db.collection")

C. db.collection.shardRange({ "field": 1 })

D. sh.shardCollection("db.collection", { "field": 1 })

Solution

1. Step 1: Recall MongoDB sharding command

   The correct command to shard a collection by a key is sh.shardCollection() with the shard key.

2. Step 2: Verify syntax correctness

   sh.shardCollection("db.collection", { "field": 1 }) uses the correct syntax: sh.shardCollection("db.collection", { "field": 1 }). Other options are invalid commands.

3. Final Answer:

   sh.shardCollection("db.collection", { "field": 1 }) -> Option D

4. Quick Check:

   Use sh.shardCollection() to enable sharding [OK]

Hint: Use sh.shardCollection() with shard key object [OK]

Common Mistakes:

• Using non-existent commands like sh.enableRangeSharding
• Incorrect method names like shardRangeCollection
• Passing wrong parameters or missing shard key

3. Given a collection sharded by the field age with ranges: { age: { $lt: 20 } }, { age: { $gte: 20, $lt: 40 } }, and { age: { $gte: 40 } }, which shard will store a document with { age: 35 }?

medium

A. Shard with range { age: { $gte: 20, $lt: 40 } }

B. Shard with range { age: { $lt: 20 } }

C. Shard with range { age: { $gte: 40 } }

D. Document will be stored on all shards

Solution

1. Step 1: Identify the correct range for age 35

   Age 35 fits in the range where age is greater or equal to 20 and less than 40.

2. Step 2: Match the range to the shard

   The shard with range { age: { $gte: 20, $lt: 40 } } will store the document.

3. Final Answer:

   Shard with range { age: { $gte: 20, $lt: 40 } } -> Option A

4. Quick Check:

   35 is between 20 and 40, so goes to that shard [OK]

Hint: Match value to shard range boundaries carefully [OK]

Common Mistakes:

• Choosing the shard with $lt: 20 incorrectly
• Assuming document is stored on all shards
• Confusing range boundaries (gte vs lt)

4. You have a range-based sharded collection on score with ranges: { score: { $lt: 50 } } and { score: { $gte: 50 } }. You try to insert { score: "high" } but get an error. What is the likely cause?

medium

A. The shard key ranges overlap causing conflict.

B. The shard key field is missing in the document.

C. The shard key value type does not match the defined range type.

D. MongoDB does not support string values in shard keys.

Solution

1. Step 1: Understand shard key type requirements

   Shard key values must match the type used in range definitions. Here, ranges expect numeric scores.

2. Step 2: Identify the error cause

   Inserting a string "high" for a numeric shard key causes a type mismatch error.

3. Final Answer:

   The shard key value type does not match the defined range type. -> Option C

4. Quick Check:

   Shard key types must match range types [OK]

Hint: Shard key values must match range data types [OK]

Common Mistakes:

• Assuming missing shard key field causes this error
• Thinking overlapping ranges cause insert errors
• Believing MongoDB disallows strings in shard keys

5. You want to shard a large user collection by signupDate using range-based sharding. Which shard key choice will best support queries filtering users by recent signup dates?

hard

A. Use { signupDate: 1 } as shard key to split by date ranges.

B. Use { userId: 1 } as shard key for even data distribution.

C. Use { signupDate: "hashed" } to hash dates for randomness.

D. Use { lastLogin: 1 } as shard key for login-based queries.

Solution

1. Step 1: Identify query pattern

   Queries filter users by recent signup dates, so shard key should support range queries on signupDate.

2. Step 2: Choose shard key matching query pattern

   Using { signupDate: 1 } enables range-based sharding by date, optimizing these queries.

3. Step 3: Evaluate other options

   Hashing or using unrelated fields won't support efficient range queries on signupDate.

4. Final Answer:

   Use { signupDate: 1 } as shard key to split by date ranges. -> Option A

5. Quick Check:

   Shard key matches query field for best performance [OK]

Hint: Match shard key to common query field for range queries [OK]

Common Mistakes:

• Choosing hashed shard key when range queries are needed
• Picking unrelated fields like userId or lastLogin
• Ignoring query patterns when selecting shard key