Puma server configuration in Ruby on Rails - Performance & Optimization

Performance: Puma server configuration

HIGH IMPACT

This affects how fast the Rails app can handle incoming web requests and how well it uses server resources.

Configuring Puma to handle concurrent web requests efficiently

Ruby on Rails

threads 5,16
workers 2

Allows multiple threads per worker and multiple workers, enabling parallel request processing.

📈 Performance GainImproves throughput and reduces request wait time under load

Configuring Puma to handle concurrent web requests efficiently

Ruby on Rails

threads 1,1
workers 1

Using only one thread and one worker limits concurrency, causing slow response under multiple requests.

📉 Performance CostBlocks requests sequentially, increasing response time and reducing throughput

Performance Comparison

Pattern	Concurrency	Memory Usage	Startup Time	Verdict
threads 1,1 workers 1	Single request at a time	Higher per worker	Slower	[X] Bad
threads 5,16 workers 2	Multiple requests concurrently	Optimized with preload	Faster	[OK] Good

Rendering Pipeline

Puma handles incoming HTTP requests by distributing them across threads and workers, which process the requests and send responses. Efficient configuration reduces queuing delays and CPU contention.

→Request Queuing

→Thread Scheduling

→Process Forking

⚠️ BottleneckInsufficient threads or workers causing request queuing delays

Core Web Vital Affected

INP

This affects how fast the Rails app can handle incoming web requests and how well it uses server resources.

Optimization Tips

1Set Puma threads to match expected concurrency for your app workload.

2Use multiple workers to utilize multiple CPU cores effectively.

3Enable preload_app! to reduce memory usage and speed up worker boot.

Performance Quiz - 3 Questions

What is the main benefit of increasing Puma worker count?

A Improves CSS rendering speed

B Allows handling more requests in parallel by using multiple processes

C Reduces memory usage by sharing threads

D Decreases database query time

DevTools: Performance (Rails logs and server monitoring)

How to check: Monitor request queue time and response time under load using Rails logs and tools like puma-status or New Relic.

What to look for: Low request queue time and consistent response times indicate good Puma configuration.

Practice

1. What is the main purpose of configuring the threads setting in a Puma server for a Rails app?

easy

A. To control how many requests Puma can handle concurrently within a single worker

B. To set the number of worker processes Puma will spawn

C. To specify the port number Puma listens on

D. To define the Rails environment (development, production, etc.)

Solution

1. Step 1: Understand the role of threads in Puma

   Threads allow Puma to handle multiple requests at the same time inside one worker process.

2. Step 2: Differentiate threads from workers and ports

   Workers are separate processes, ports define network access, threads are about concurrency inside a worker.

3. Final Answer:

   To control how many requests Puma can handle concurrently within a single worker -> Option A

4. Quick Check:

   Threads = concurrent requests per worker [OK]

Hint: Threads = concurrent requests per worker process [OK]

Common Mistakes:

• Confusing threads with workers
• Thinking threads set the port
• Mixing threads with environment settings

2. Which of the following is the correct syntax to set Puma to listen on port 3000 in the configuration file?

easy

A. bind 'tcp://3000'

B. set_port 3000

C. listen 3000

D. port 3000

Solution

1. Step 1: Recall Puma configuration syntax for port

   Puma uses the simple directive port followed by the port number.

2. Step 2: Check other options for correctness

   set_port and listen are not valid Puma config commands; bind requires a full URL, not just a port number.

3. Final Answer:

   port 3000 -> Option D

4. Quick Check:

   Use port to set listening port [OK]

Hint: Use 'port' keyword followed by number [OK]

Common Mistakes:

• Using 'listen' instead of 'port'
• Omitting quotes in 'bind' URL
• Using non-existent 'set_port' command

3. Given this Puma config snippet:

threads 5, 5
workers 2
port 4000

How many total threads can Puma handle at once across all workers?

medium

A. 5

B. 10

C. 2

D. 20

Solution

1. Step 1: Understand threads and workers relationship

   Each worker runs with 5 threads, and there are 2 workers.

2. Step 2: Calculate total threads

   Total threads = threads per worker * number of workers = 5 * 2 = 10. But note the config uses 'threads 5, 5' which means min and max threads are 5, so max threads per worker is 5.

3. Step 3: Re-examine the question carefully

   Actually, the question asks total threads Puma can handle at once across all workers. Since each worker has 5 threads, and there are 2 workers, total is 5 * 2 = 10.

4. Final Answer:

   10 -> Option B

5. Quick Check:

   Threads per worker * workers = 10 [OK]

Hint: Multiply threads by workers for total concurrency [OK]

Common Mistakes:

• Confusing min and max threads
• Ignoring number of workers
• Assuming threads is total, not per worker

4. You added preload_app! in your Puma config but your Rails app crashes on worker boot with a database connection error. What is the most likely fix?

medium

A. Increase the number of workers

B. Remove preload_app! from the config

C. Add a on_worker_boot block to reconnect ActiveRecord

D. Change the port number to 8080

Solution

1. Step 1: Understand what preload_app! does

   It loads the app before workers fork, so connections like database must be re-established in each worker.

2. Step 2: Fix database connection error on worker boot

   Use on_worker_boot block to reconnect ActiveRecord to the database after forking.

3. Final Answer:

   Add a on_worker_boot block to reconnect ActiveRecord -> Option C

4. Quick Check:

   Use on_worker_boot to fix DB connections [OK]

Hint: Reconnect DB in on_worker_boot after preload_app! [OK]

Common Mistakes:

• Removing preload_app! instead of fixing connections
• Changing unrelated settings like port
• Increasing workers without fixing connections

5. You want Puma to run with 3 workers and a thread pool between 2 and 6 threads per worker. You also want to ensure your Rails app reconnects to the database properly after forking. Which Puma config snippet correctly achieves this?

hard

A. threads 2, 6\nworkers 3\npreload_app!\non_worker_boot do\n ActiveRecord::Base.establish_connection\nend

B. workers 3\nthreads 6, 2\npreload_app!\non_worker_boot do\n ActiveRecord::Base.connection.disconnect!\nend

C. threads 2, 6\nworkers 3\nport 3000\non_worker_boot do\n ActiveRecord::Base.establish_connection\nend

D. workers 3\nthreads 2, 6\npreload_app!\non_worker_boot do\n ActiveRecord::Base.connection.reconnect!\nend

Solution

1. Step 1: Set threads and workers correctly

   Threads should be set as threads 2, 6 for min and max, and workers as 3.

2. Step 2: Use preload_app! and reconnect DB properly

   preload_app! must be present, and on_worker_boot should call ActiveRecord::Base.establish_connection to reconnect DB.

3. Step 3: Check each option for correctness

   threads 2, 6\nworkers 3\npreload_app!\non_worker_boot do\n ActiveRecord::Base.establish_connection\nend matches all requirements. workers 3\nthreads 6, 2\npreload_app!\non_worker_boot do\n ActiveRecord::Base.connection.disconnect!\nend reverses thread min/max and disconnects DB incorrectly. threads 2, 6\nworkers 3\nport 3000\non_worker_boot do\n ActiveRecord::Base.establish_connection\nend misses preload_app!. workers 3\nthreads 2, 6\npreload_app!\non_worker_boot do\n ActiveRecord::Base.connection.reconnect!\nend uses a non-existent reconnect! method.

4. Final Answer:

   threads 2, 6 workers 3 preload_app! on_worker_boot do ActiveRecord::Base.establish_connection end -> Option A

5. Quick Check:

   Correct threads, workers, preload_app!, and DB reconnect [OK]

Hint: Use preload_app! with on_worker_boot to reconnect DB [OK]

Common Mistakes:

• Swapping min and max threads
• Omitting preload_app!
• Using wrong DB reconnect method