Persisted queries in GraphQL - Step-by-Step Execution

Concept Flow - Persisted queries

Client prepares query

↓

Check if query is persisted?

Yes→Send query ID only

↓

Server looks up query

↓

Send full query to server

↓

Execute stored query

↓

Server stores query

↓

Return result

↓

Execute query

↓

Client receives data

Client sends queries; if query is new, server stores it and executes; later client sends only query ID for faster execution.

Execution Sample

GraphQL

mutation PersistQuery {
  persistQuery(query: "{ user { id name } }") {
    id
  }
}

query GetUser {
  user {
    id
    name
  }
}

First, client sends a mutation to store the query and get an ID; later client sends query ID to fetch user data.

Execution Table

Step	Action	Input	Server Behavior	Output
1	Client sends persistQuery mutation	{ user { id name } }	Stores query, generates ID 'abc123'	{ id: "abc123" }
2	Client sends query with ID 'abc123'	ID: 'abc123'	Looks up stored query by ID	Executes query and returns user data
3	Server returns user data	N/A	N/A	{ user: { id: "1", name: "Alice" } }
4	Client receives data	N/A	N/A	User data displayed

💡 Execution stops after client receives the requested data.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
query	null	{ user { id name } }	ID 'abc123'	Stored query fetched	Executed query result
queryID	null	'abc123'	'abc123'	'abc123'	'abc123'
response	null	{ id: "abc123" }	User data	User data	User data

Key Moments - 2 Insights

Why does the client send only the query ID after the first time?

Because the server has stored the full query linked to that ID (see execution_table step 2), so sending only the ID saves bandwidth and speeds up the request.

What happens if the client sends a query ID that the server does not recognize?

The server cannot find the stored query and will return an error or ask the client to send the full query again (not shown in this trace but important to know).

Visual Quiz - 3 Questions

Look at the execution_table, what does the server return after storing the query in step 1?

A Error message

B { id: 'abc123' }

C User data

D Empty response

💡 Hint

Check the Output column in step 1 of execution_table.

At which step does the server execute the stored query?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the Server Behavior and Output columns in steps 2 and 3.

If the client sends a new query instead of an ID, what would happen according to the flow?

A Server executes the new query and stores it

B Server rejects the query

C Server returns cached data

D Client receives an error

💡 Hint

Refer to the concept_flow where new queries are stored and executed.

Concept Snapshot

Persisted queries let clients send a query once to store it on the server.
Later, clients send only the query ID to run the stored query.
This reduces data sent and speeds up requests.
If the server doesn't recognize the ID, it asks for the full query again.
Common in GraphQL to optimize network usage.

Full Transcript

Persisted queries are a way to optimize GraphQL requests. First, the client sends the full query to the server using a special mutation to store it. The server saves the query and returns a unique ID. Later, the client sends only this ID to request data. The server looks up the stored query by ID, executes it, and returns the result. This saves bandwidth and speeds up communication. If the client sends an unknown ID, the server will ask for the full query again. This process helps reduce repeated sending of large queries over the network.

Practice

1. What is the main benefit of using persisted queries in GraphQL?

easy

A. The server stores user credentials for faster login.

B. Clients send only a unique ID instead of the full query, saving bandwidth.

C. Queries are automatically optimized by the client.

D. It allows clients to write queries without validation.

Solution

1. Step 1: Understand what persisted queries do

   Persisted queries store the full GraphQL query on the server with a unique ID.

2. Step 2: Identify the client-server interaction

   Clients send only the ID to run the query, reducing the data sent over the network.

3. Final Answer:

   Clients send only a unique ID instead of the full query, saving bandwidth. -> Option B

4. Quick Check:

   Persisted queries reduce data sent = Clients send only a unique ID instead of the full query, saving bandwidth. [OK]

Hint: Persisted queries send IDs, not full queries [OK]

Common Mistakes:

• Thinking clients send full queries every time
• Confusing persisted queries with client-side caching
• Believing persisted queries store user data

2. Which of the following is the correct way to send a persisted query request in GraphQL?

easy

A. { "id": "12345", "variables": { "userId": "1" } }

B. { "query": "{ user(id: 1) { name } }" }

C. { "mutation": "updateUser" }

D. { "headers": { "Authorization": "token" } }

Solution

1. Step 1: Identify the persisted query request format

   Persisted queries send the unique query ID and variables, not the full query string.

2. Step 2: Match the correct JSON structure

   { "id": "12345", "variables": { "userId": "1" } } sends an ID and variables, which is the correct persisted query format.

3. Final Answer:

   { "id": "12345", "variables": { "userId": "1" } } -> Option A

4. Quick Check:

   Persisted query request = ID + variables [OK]

Hint: Persisted queries use ID field, not full query [OK]

Common Mistakes:

• Sending full query instead of ID
• Using mutation key instead of id
• Confusing headers with query payload

3. Given the following persisted query setup, what will the server return when the client sends { "id": "abc123", "variables": { "limit": 5 } } if the query with ID abc123 fetches the first limit users?

Assume the database has 10 users named User1 to User10.

Options:

medium

A. []

B. [{"name": "User6"}, {"name": "User7"}, {"name": "User8"}, {"name": "User9"}, {"name": "User10"}]

C. [{"name": "User1"}, {"name": "User2"}, {"name": "User3"}, {"name": "User4"}, {"name": "User5"}]

D. Error: Query ID not found

Solution

1. Step 1: Understand the query and variables

   The query with ID 'abc123' fetches users limited by the 'limit' variable, which is 5 here.

2. Step 2: Determine the expected result

   Since the database has users User1 to User10, fetching the first 5 returns User1 to User5.

3. Final Answer:

   [{"name": "User1"}, {"name": "User2"}, {"name": "User3"}, {"name": "User4"}, {"name": "User5"}] -> Option C

4. Quick Check:

   Limit 5 users returns first 5 users [OK]

Hint: Variables control query output; check their values [OK]

Common Mistakes:

• Assuming query returns last users
• Thinking ID is invalid
• Ignoring variables in query

4. A developer tries to use persisted queries but gets an error: Query ID not found. What is the most likely cause?

medium

A. The client sent a query ID that the server does not recognize.

B. The client sent the full query instead of the ID.

C. The server does not support GraphQL.

D. The client forgot to include variables.

Solution

1. Step 1: Analyze the error message

   The error 'Query ID not found' means the server cannot find the query matching the sent ID.

2. Step 2: Identify the cause

   This usually happens if the client sends an ID that was never registered or stored on the server.

3. Final Answer:

   The client sent a query ID that the server does not recognize. -> Option A

4. Quick Check:

   Unknown query ID causes 'Query ID not found' error [OK]

Hint: Check if query ID is registered on server [OK]

Common Mistakes:

• Assuming full query sent causes this error
• Blaming missing variables for this error
• Thinking server lacks GraphQL support

5. You want to secure your GraphQL API by allowing only persisted queries. Which approach best achieves this?

hard

A. Disable persisted queries and use API keys instead.

B. Allow all queries but log those without IDs for review.

C. Require clients to send full queries and IDs together.

D. Reject any request that does not include a valid persisted query ID.

Solution

1. Step 1: Understand API security with persisted queries

   Allowing only persisted queries means the server accepts requests only if they have a valid stored query ID.

2. Step 2: Identify the best enforcement method

   Rejecting requests without valid IDs ensures only approved queries run, improving security.

3. Final Answer:

   Reject any request that does not include a valid persisted query ID. -> Option D

4. Quick Check:

   Only accept valid persisted query IDs to secure API [OK]

Hint: Block requests missing valid persisted query IDs [OK]

Common Mistakes:

• Allowing all queries weakens security
• Sending full queries defeats persisted query purpose
• Relying only on API keys without query control