Idempotency tokens in DynamoDB - Step-by-Step Execution

Concept Flow - Idempotency tokens

Client sends request with token

↓

Check if token exists in DB?

Yes→Return previous result

No↓

Process request

↓

Store token and result

↓

Return new result

The system checks if the idempotency token was used before. If yes, it returns the old result. If no, it processes and stores the result with the token.

Execution Sample

DynamoDB

1. Client sends request with token 'abc123'
2. System checks DB for 'abc123'
3. Token not found, process request
4. Store 'abc123' with result
5. Return result to client

This example shows how a request with an idempotency token is handled to avoid duplicate processing.

Execution Table

Step	Action	Token Exists?	Process Request?	Store Token?	Return Result
1	Receive request with token 'abc123'	Unknown	No	No	No
2	Check DB for token 'abc123'	No	No	No	No
3	Token not found, process request	No	Yes	No	No
4	Store token 'abc123' with result	No	No	Yes	No
5	Return new result to client	No	No	No	Yes
6	Receive duplicate request with token 'abc123'	Unknown	No	No	No
7	Check DB for token 'abc123'	Yes	No	No	No
8	Token found, skip processing	Yes	No	No	No
9	Return stored result to client	Yes	No	No	Yes

💡 Execution stops after returning result to client, either new or stored.

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 7	Final
token_exists_in_db	Unknown	No	Yes	Yes	Yes
request_processed	No	No	Yes	No	No
token_stored	No	No	Yes	Yes	Yes
result_returned	No	No	No	No	Yes

Key Moments - 2 Insights

Why does the system check if the token exists before processing?

To avoid doing the same work twice. If the token exists (see step 7 in execution_table), the system returns the old result instead of processing again.

What happens if the token is not found in the database?

The system processes the request (step 3), stores the token with the result (step 4), and then returns the new result (step 5).

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the system decide to process the request?

A Step 3

B Step 2

C Step 7

D Step 9

💡 Hint

Check the 'Process Request?' column in the execution_table.

According to variable_tracker, what is the value of 'token_exists_in_db' after step 4?

A Unknown

B Yes

C No

D Not applicable

💡 Hint

Look at the 'token_exists_in_db' row and the 'After Step 4' column.

If the client sends the same token again, what does the system do according to the execution_table?

A Processes the request again

B Returns an error

C Returns the stored result without processing

D Deletes the token and processes again

💡 Hint

See steps 7 to 9 in the execution_table.

Concept Snapshot

Idempotency tokens prevent duplicate processing.
Client sends a unique token with each request.
System checks if token exists in DB.
If yes, returns stored result.
If no, processes request and stores token with result.
Ensures safe retries without side effects.

Full Transcript

Idempotency tokens are unique identifiers sent with requests to ensure the same operation is not performed multiple times. When a request arrives, the system checks if the token already exists in the database. If it does, the system returns the previously stored result, avoiding duplicate work. If the token is new, the system processes the request, stores the token and result, and returns the new result. This mechanism helps in safely retrying requests without causing unintended repeated actions.