Difficulty: Medium
Correct Answer: mysql_connect opens a normal connection that closes at the end of the script, while mysql_pconnect opens a persistent connection that is kept open and reused
Explanation:
Introduction / Context:
Before modern extensions such as mysqli and PDO became standard, PHP commonly used the mysql extension to connect to MySQL databases. That extension provided two similar functions, mysql_connect and mysql_pconnect. Understanding the distinction between them is useful for interpreting legacy code and exam questions, even though the mysql extension is now deprecated. This question asks about the behavioural difference between these two connection functions.
Given Data / Assumptions:
Concept / Approach:
mysql_connect opens a non persistent database connection. This connection is created when the script calls the function and is automatically closed at the end of the script execution. mysql_pconnect, on the other hand, opens a persistent connection that is not closed when the script ends. Instead, it is kept alive and may be reused by subsequent scripts in the same process that request a connection with the same parameters. Persistent connections can reduce connection overhead but also require careful management to avoid exhausting server resources or leaving stale state in sessions.
Step-by-Step Solution:
Step 1: Recall that mysql_connect establishes a connection that is tied to the lifetime of the PHP script handling the current request.Step 2: Understand that when the script finishes, PHP closes non persistent connections created with mysql_connect, freeing resources.Step 3: Recognise that mysql_pconnect attempts to reuse an existing persistent connection if one with the same host, user, and password already exists for the process.Step 4: Note that persistent connections survive across requests in a pooled manner, which can reduce connect or disconnect overhead but may hold resources longer.Step 5: Conclude that the main difference is persistence across requests, not server location or read versus write usage.
Verification / Alternative check:
In legacy environments, you can observe the difference by monitoring open MySQL connections while sending repeated requests to a script that uses mysql_connect versus mysql_pconnect. The former will show connections being created and closed with each request, while the latter will tend to reuse a smaller set of long lived connections. Documentation about the mysql extension also clearly states that the p stands for persistent and explains the reuse behaviour, confirming this interpretation.
Why Other Options Are Wrong:
Option B claims that mysql_connect is limited to local servers and mysql_pconnect to remote ones, which is not true; both can connect to any host as long as credentials are valid. Option C divides them into read and write roles, which is not how the functions are designed; read or write permissions depend on user privileges, not which function is used. Option D says there is no difference, ignoring the important distinction in connection lifecycle. These statements do not accurately describe the behaviour of these functions.
Common Pitfalls:
A common pitfall with persistent connections is failing to reset connection state between uses, for example leftover transactions or session variables, which can lead to subtle bugs. Another issue is overestimating the performance gains and using persistent connections without monitoring resource usage, which can exhaust the maximum number of connections allowed by the database server. Modern PHP code should use mysqli or PDO with connection pooling features provided by the environment instead of relying on the old mysql extension, but understanding these differences remains useful for maintaining older applications.
Final Answer:
Correct answer: mysql_connect opens a normal connection that closes at the end of the script, while mysql_pconnect opens a persistent connection that is kept open and reused
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