PHP process model per request - Cheat Sheet & Quick Revision

Recall & Review

beginner

What happens to a PHP script during a single web request?

The PHP script is loaded, executed from start to finish, and then the process ends. Each request starts a new process or thread that runs the script independently.

beginner

Why does PHP use a process model per request?

To keep each request isolated, so errors or data from one request do not affect others. This makes PHP simple and secure for web applications.

beginner

How does PHP handle variables and memory between requests?

Variables and memory are created fresh for each request and destroyed when the request ends. PHP does not keep variables or memory between requests.

intermediate

What is the role of the web server in PHP's process model?

The web server receives the request, starts a PHP process or thread to run the script, then sends the output back to the client after the script finishes.

intermediate

How does PHP's process model affect performance?

Starting a new process for each request adds some overhead, but PHP uses techniques like opcode caching to speed up execution and reduce delays.

What happens to PHP variables after a web request finishes?

A They are sent to the client browser

B They are saved automatically for the next request

C They are destroyed and do not persist to the next request

D They become global variables

PHP variables exist only during the request and are destroyed afterward to keep requests isolated.

Which component starts the PHP process for each request?

A The client browser

B The operating system scheduler

C The database

D The web server

The web server receives the request and starts the PHP process to run the script.

Why does PHP create a new process for each request?

A To isolate requests and avoid data sharing

B To save memory between requests

C To keep variables persistent

D To speed up the server startup

Isolating requests prevents errors or data leaks between users.

What technique helps PHP reduce the overhead of starting a process each request?

A Opcode caching

B Database indexing

C Client-side scripting

D Session cookies

Opcode caching stores compiled code to speed up script execution.

In PHP's process model, when does the script execution end?

A When the user logs out

B At the end of the request

C After 10 requests

D When the server restarts

Each script runs only during its request and ends when the request finishes.

Explain how PHP handles a web request from start to finish in its process model.

Think about what happens each time you load a PHP page in your browser.

Describe the advantages and disadvantages of PHP's process model per request.

Consider both how it helps and what challenges it creates.

Practice

1. What happens to PHP variables after a web request finishes?

easy

A. They become global variables accessible by all users

B. They keep their values for the next request automatically

C. They are stored permanently in the server memory

D. They are reset and lost unless saved externally

Solution

1. Step 1: Understand PHP request lifecycle

   PHP starts fresh for each request, so variables exist only during that request.

2. Step 2: Identify variable persistence

   Variables reset after request ends unless saved in sessions or databases.

3. Final Answer:

   They are reset and lost unless saved externally -> Option D

4. Quick Check:

   PHP variables reset each request = D [OK]

Hint: Remember: PHP starts fresh every request, no variable memory [OK]

Common Mistakes:

• Thinking variables persist automatically between requests
• Confusing PHP with long-running server processes
• Assuming global variables keep values across users

2. Which PHP code snippet correctly shows the start of a new request process?

easy

A.

B.

C.

D.

Solution

1. Step 1: Analyze variable initialization

   In a new request, variables start fresh; $count = 0 sets it properly.

2. Step 2: Check other options for persistence

   Options A, B, D try to increment without initialization or rely on static/session which need extra setup.

3. Final Answer:

   <?php $count = 0; echo $count; ?> -> Option C

4. Quick Check:

   New request means fresh variables = C [OK]

Hint: Fresh request means variables start from scratch [OK]

Common Mistakes:

• Assuming static variables keep value across requests
• Using session without starting it
• Incrementing uninitialized variables

3. What will be the output of this PHP code when run twice in separate requests?

<?php
session_start();
if (!isset($_SESSION['visits'])) {
  $_SESSION['visits'] = 1;
} else {
  $_SESSION['visits']++;
}
echo $_SESSION['visits'];
?>

medium

A. 1 then 2

B. 1 then 1

C. 2 then 3

D. Error on second request

Solution

1. Step 1: Understand session persistence

   Session data keeps values across requests, so visits count increases.

2. Step 2: Trace two requests

   First request sets visits=1; second request increments to 2.

3. Final Answer:

   1 then 2 -> Option A

4. Quick Check:

   Session stores visits count = 1 then 2 [OK]

Hint: Sessions keep data between requests, variables do not [OK]

Common Mistakes:

• Thinking variables persist without sessions
• Forgetting to call session_start()
• Expecting static variables to persist across requests

4. Identify the error in this PHP code snippet that tries to keep a counter across requests:

<?php
$count = 0;
$count++;
echo $count;
?>

medium

A. Variables reset each request, so counter never increases

B. Syntax error due to missing semicolon

C. Session not started, so counter is undefined

D. Static variable needed to keep count

Solution

1. Step 1: Check variable behavior per request

   $count is set to 0 every time, so increment always starts fresh.

2. Step 2: Identify persistence issue

   Without sessions or external storage, counter resets each request.

3. Final Answer:

   Variables reset each request, so counter never increases -> Option A

4. Quick Check:

   Variables reset each request = A [OK]

Hint: Variables reset each request; use sessions to persist [OK]

Common Mistakes:

• Assuming static variables persist across requests
• Confusing syntax errors with logic errors
• Forgetting to start sessions for persistence

5. You want to count unique visitors to your PHP website. Which approach correctly uses PHP's process model per request to achieve this?

hard

A. Use a static variable in PHP script to count visitors

B. Store visitor count in a database and increment on each request

C. Increment a PHP variable without sessions or storage

D. Rely on PHP variables to keep count across requests

Solution

1. Step 1: Understand PHP process model limits

   PHP variables reset each request, so they can't keep visitor count.

2. Step 2: Identify persistent storage method

   Database stores data permanently and can be updated each request.

3. Final Answer:

   Store visitor count in a database and increment on each request -> Option B

4. Quick Check:

   Persistent storage needed for visitor count = A [OK]

Hint: Use database or sessions to save data beyond request [OK]

Common Mistakes:

• Using static or normal variables expecting persistence
• Ignoring need for external storage
• Confusing sessions with static variables