Partition key selection in DynamoDB - Step-by-Step Execution

Concept Flow - Partition key selection

Start: Insert item

↓

Extract partition key value

↓

Apply hash function on partition key

↓

Calculate partition (physical storage)

↓

Store item in partition

↓

End

When adding data, DynamoDB uses the partition key value to decide where to store the item by hashing it to a partition.

Execution Sample

DynamoDB

INSERT INTO Table
  (PartitionKey, SortKey, Data)
VALUES
  ('User123', '2024-06-01', 'OrderData')

This inserts an item with partition key 'User123' which DynamoDB hashes to find the storage partition.

Execution Table

Step	Action	Partition Key Value	Hash Result	Partition Selected	Result
1	Start insert	User123			Preparing to insert item
2	Extract partition key	User123			Partition key identified
3	Apply hash function	User123	0x5a3f1c		Hash calculated from key
4	Calculate partition		0x5a3f1c	Partition 7	Partition chosen based on hash
5	Store item			Partition 7	Item stored in partition 7
6	End				Insert complete

💡 Item stored after hashing partition key and selecting partition

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
PartitionKey		User123	User123	User123	User123
HashResult			0x5a3f1c	0x5a3f1c	0x5a3f1c
PartitionSelected				Partition 7	Partition 7

Key Moments - 2 Insights

Why does DynamoDB hash the partition key instead of using it directly?

Hashing the partition key evenly distributes data across partitions to avoid hotspots, as shown in step 3 and 4 of the execution_table.

What happens if two items have the same partition key?

They hash to the same partition, so they are stored together but distinguished by the sort key or other attributes, implied by the partition selection in step 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the hash result of the partition key 'User123'?

A 0x5a3f1c

B Partition 7

C User123

D 0x7b2d9f

💡 Hint

Check the 'Hash Result' column at step 3 in the execution_table

At which step is the partition selected based on the hash?

A Step 2

B Step 5

C Step 4

D Step 3

💡 Hint

Look at the 'Partition Selected' column in the execution_table

If the partition key changes, how does it affect the partition selected?

A Partition stays the same

B Partition changes because hash changes

C Partition key does not affect partition

D Partition is random

💡 Hint

Refer to variable_tracker showing how PartitionSelected depends on HashResult which depends on PartitionKey

Concept Snapshot

Partition key selection in DynamoDB:
- Partition key uniquely identifies item partition
- DynamoDB hashes partition key value
- Hash determines physical partition
- Even data distribution avoids hotspots
- Items with same partition key go to same partition

Full Transcript

When you insert an item into DynamoDB, the system takes the partition key value from your item. It then applies a hash function to this key to get a hash value. This hash value is used to decide which physical partition will store your item. This process ensures data is spread evenly across partitions, preventing any single partition from becoming overloaded. Items with the same partition key hash to the same partition, allowing efficient queries. The execution steps show extracting the key, hashing it, selecting the partition, and storing the item.