Range-based sharding in MongoDB - Step-by-Step Execution

Concept Flow - Range-based sharding

Start: Insert Document

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Extract Shard Key Value

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Compare Value to Ranges

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Find Matching Shard Range

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Route Document to Shard

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Store Document in Shard

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End

Documents are routed to shards by comparing their shard key value to defined ranges, then stored in the matching shard.

Execution Sample

MongoDB

sh.enableSharding("mydb")
sh.shardCollection("mydb.users", { age: 1 })
// Define ranges:
// Shard1: age < 30
// Shard2: 30 <= age < 60
// Shard3: age >= 60

// Insert document {name: "Alice", age: 25}

This example enables sharding on a collection by age, defines ranges for shards, and inserts a document to be routed.

Execution Table

Step	Action	Shard Key Value	Range Checked	Shard Selected	Result
1	Insert document {name: "Alice", age: 25}	25	age < 30	Shard1	Document routed to Shard1
2	Insert document {name: "Bob", age: 45}	45	30 <= age < 60	Shard2	Document routed to Shard2
3	Insert document {name: "Carol", age: 65}	65	age >= 60	Shard3	Document routed to Shard3
4	Insert document {name: "Dave", age: 30}	30	30 <= age < 60	Shard2	Document routed to Shard2
5	Insert document {name: "Eve", age: 29}	29	age < 30	Shard1	Document routed to Shard1
6	No more documents	-	-	-	End of routing

💡 All documents routed to shards based on their age falling into defined ranges.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
Shard Key Value	-	25	45	65	30	29	-
Shard Selected	-	Shard1	Shard2	Shard3	Shard2	Shard1	-

Key Moments - 2 Insights

Why does the document with age 30 go to Shard2 and not Shard1?

Because the range for Shard1 is age < 30, so 30 is not included there. The range for Shard2 is 30 <= age < 60, so 30 fits in Shard2's range as shown in execution_table row 4.

What happens if a document's shard key value does not fit any defined range?

In range-based sharding, all possible values should be covered by ranges. If not, the document cannot be routed properly. This example assumes full coverage, so no such case appears in the execution_table.

Visual Quiz - 3 Questions

Look at the execution table, which shard does the document with age 65 get routed to?

A Shard3

B Shard1

C Shard2

D None

💡 Hint

Check row 3 in the execution_table where age 65 is routed.

At which step does the shard key value equal 30?

A Step 2

B Step 4

C Step 5

D Step 1

💡 Hint

Look at the Shard Key Value column in execution_table.

If the range for Shard1 changed to age <= 30, where would the document with age 30 be routed?

A Shard3

B Shard2

C Shard1

D Cannot be determined

💡 Hint

Consider how the range comparison changes and check the routing logic in concept_flow.

Concept Snapshot

Range-based sharding routes documents by shard key value ranges.
Define continuous, non-overlapping ranges for shards.
Insertions compare shard key to ranges to pick shard.
Example: age < 30 → Shard1, 30 ≤ age < 60 → Shard2, age ≥ 60 → Shard3.
Ensure all values fit some range to avoid routing errors.

Full Transcript

Range-based sharding in MongoDB splits data by ranges of a shard key. When a document is inserted, the system looks at the shard key value and compares it to the defined ranges. It finds which range the value fits in and sends the document to the corresponding shard. For example, if the shard key is age, and ranges are set as age less than 30 for Shard1, age between 30 and 59 for Shard2, and age 60 or more for Shard3, then a document with age 25 goes to Shard1, age 45 to Shard2, and age 65 to Shard3. This method helps keep related data together and balances load. It is important that the ranges cover all possible values so every document can be routed correctly.