Job options (delay, attempts, priority) in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

Understanding delay option in NestJS Bull jobs

What will be the behavior of a job scheduled with a delay of 5000 milliseconds in NestJS Bull queue?

NestJS

queue.add('sendEmail', { userId: 123 }, { delay: 5000 });

A The job will wait 5 seconds before it becomes eligible for processing.

B The job will be retried 5 times with 1 second delay between retries.

C The job will be assigned the highest priority and processed first.

D The job will start processing immediately after being added to the queue.

💡 Hint

Think about what the delay option controls in job scheduling.

The delay option specifies how long the job should wait before it is processed. A delay of 5000 means the job will be delayed for 5 seconds.

❓ state_output

intermediate

Effect of attempts option on job retries

If a job is configured with { attempts: 3 } and it fails twice before succeeding, how many times will the job processor run?

NestJS

queue.add('processData', { data: 'info' }, { attempts: 3 });

A The processor will run 1 time only.

B The processor will run 2 times total.

C The processor will run 4 times total.

D The processor will run 3 times total.

💡 Hint

Remember that attempts count includes the first try plus retries.

The attempts option sets the maximum number of tries including the first attempt. So 3 attempts means the job can run up to 3 times if it keeps failing.

📝 Syntax

advanced

Correct syntax for setting job priority in NestJS Bull

Which option correctly sets a job priority of 10 when adding a job to a Bull queue in NestJS?

NestJS

queue.add('generateReport', { reportId: 42 }, ???);

A { priority: 10 }

B { priority: '10' }

C { priority: true }

D { priority: -10 }

💡 Hint

Priority should be a positive integer number.

The priority option expects a positive integer. Strings or booleans are invalid and negative numbers lower priority.

🔧 Debug

advanced

Identifying error with invalid delay value

What error will occur if you set delay to a negative number like -1000 in a Bull job options?

NestJS

queue.add('cleanup', {}, { delay: -1000 });

A RangeError: Delay must be a positive integer

B TypeError: Delay option must be a string

C No error, job will be processed immediately

D SyntaxError: Unexpected token '-'

💡 Hint

Think about what negative delay means for scheduling.

Bull does not throw an error for negative delay values. The job timestamp will be in the past, causing it to be processed immediately.

🧠 Conceptual

expert

How priority affects job processing order in Bull queues

Given three jobs added with priorities 5, 10, and 1 respectively, in what order will Bull process them assuming no delay or attempts?

NestJS

queue.add('job1', {}, { priority: 5 });
queue.add('job2', {}, { priority: 10 });
queue.add('job3', {}, { priority: 1 });

A job3, job1, job2

B job2, job1, job3

C job1, job2, job3

D job1, job3, job2

💡 Hint

Higher priority numbers mean higher priority in Bull.

Bull processes jobs with higher priority numbers first. So priority 10 runs before 5, which runs before 1.

Practice

1. In NestJS job queues, what does the delay option do when adding a job?

easy

A. It sets the maximum number of retries for the job.

B. It postpones the job execution by a specified time.

C. It assigns the job a priority level.

D. It cancels the job immediately.

Solution

1. Step 1: Understand the purpose of delay in job options

   The delay option is used to postpone when a job starts running after being added to the queue.

2. Step 2: Compare with other options

   attempts controls retries, priority controls order, so they do not delay execution.

3. Final Answer:

   It postpones the job execution by a specified time. -> Option B

4. Quick Check:

   delay = postpone job start [OK]

Hint: Delay means wait before running the job [OK]

Common Mistakes:

• Confusing delay with attempts (retry count)
• Thinking delay sets job priority
• Assuming delay cancels the job

2. Which of the following is the correct way to add a job with 3 retry attempts and a 5-second delay in NestJS?

easy

A. queue.add('jobName', data, { retries: 3, wait: 5000 })

B. queue.add('jobName', data, { delay: 3, attempts: 5000 })

C. queue.add('jobName', data, { attempts: '3', delay: '5000' })

D. queue.add('jobName', data, { attempts: 3, delay: 5000 })

Solution

1. Step 1: Identify correct option keys and values

   The correct keys are attempts for retries and delay for postponing in milliseconds.

2. Step 2: Check value types and order

   Values must be numbers, not strings. queue.add('jobName', data, { attempts: 3, delay: 5000 }) uses correct keys and numeric values.

3. Final Answer:

   queue.add('jobName', data, { attempts: 3, delay: 5000 }) -> Option D

4. Quick Check:

   Correct keys and numeric values = queue.add('jobName', data, { attempts: 3, delay: 5000 }) [OK]

Hint: Use numeric attempts and delay keys exactly [OK]

Common Mistakes:

• Using wrong keys like retries or wait
• Passing numbers as strings
• Swapping delay and attempts values

3. Given this code snippet, what will be the order of job execution?

queue.add('job1', data1, { priority: 2 });
queue.add('job2', data2, { priority: 1 });
queue.add('job3', data3, { priority: 3 });

medium

A. job2, job1, job3

B. job3, job1, job2

C. job1, job2, job3

D. job1, job3, job2

Solution

1. Step 1: Understand priority values

   Lower priority number means higher priority and runs first.

2. Step 2: Order jobs by priority

   job2 has priority 1 (highest), job1 priority 2, job3 priority 3 (lowest).

3. Final Answer:

   job2, job1, job3 -> Option A

4. Quick Check:

   Lower priority number runs first = job2, job1, job3 [OK]

Hint: Lower priority number runs first [OK]

Common Mistakes:

• Assuming higher number means higher priority
• Ignoring priority and using add order
• Mixing up job names and priorities

4. Identify the error in this job addition code:

queue.add('emailJob', data, { delay: '1000', attempts: 5 });

medium

A. The attempts option is invalid and should be removed.

B. The job name must be an object, not a string.

C. The delay value should be a number, not a string.

D. The data parameter is missing.

Solution

1. Step 1: Check types of job options

   delay expects a number in milliseconds, but here it is a string '1000'.

2. Step 2: Validate other parameters

   attempts is valid, job name as string is correct, data is present.

3. Final Answer:

   The delay value should be a number, not a string. -> Option C

4. Quick Check:

   delay must be number, not string [OK]

Hint: Delay must be number type, not string [OK]

Common Mistakes:

• Passing delay as string instead of number
• Removing valid attempts option
• Thinking job name must be object

5. You want to add a job that should run after 10 seconds, retry up to 4 times if it fails, and run before other jobs with default priority. Which job options object is correct?

hard

A. { delay: 10000, attempts: 4 }

B. { delay: 10000, attempts: 4, priority: 1 }

C. { attempts: 4, priority: 0 }

D. { delay: 10000, priority: 0 }

Solution

1. Step 1: Understand default priority

   If priority is not set, jobs have default priority (usually 0 or normal). To run before others, priority must be lower number.

2. Step 2: Check options for delay and attempts

   Delay 10000 ms (10 seconds) and attempts 4 are required. Priority is optional if default is acceptable.

3. Step 3: Analyze options

   { delay: 10000, attempts: 4, priority: 1 } sets priority to 1 (lower priority than default 0), so it runs after default priority jobs. { delay: 10000, attempts: 4 } omits priority, so default priority applies, running before jobs with priority 1.

4. Final Answer:

   { delay: 10000, attempts: 4 } -> Option A

5. Quick Check:

   Delay + attempts with default priority = { delay: 10000, attempts: 4 } [OK]

Hint: Omit priority for default; delay and attempts must be set [OK]

Common Mistakes:

• Setting priority higher than default to run first
• Forgetting delay or attempts
• Assuming priority 0 is higher than 1