是否必须使用mysqli_free_result()？不使用该函数会有什么影响？

Great question—let’s unpack this step by step, since it’s a common point of confusion for folks moving between PHP/MySQL versions.

Short answer: No, it’s not strictly required—but it’s a best practice in specific scenarios. Here’s why:

• PHP automatically cleans up all result set resources when your script finishes executing. If you’re writing a typical short-lived web script (like processing a single request and exiting), you can skip calling it without immediate consequences.
• That said, if you’re working with long-running scripts (e.g., daemon processes, scripts that loop through hundreds/thousands of queries), or using persistent database connections, manually freeing results becomes important to avoid unnecessary memory bloat.

The impact depends entirely on your script’s context:

• Short-lived web scripts: Almost nothing. Once the script ends, PHP’s garbage collector will release the memory used by the result set, and the MySQL server will clean up its side of the resources once the connection closes.
• Long-running/resource-heavy scripts: Over time, unclosed result sets will accumulate in memory. This can lead to hitting PHP’s memory_limit threshold, causing script crashes, or tying up MySQL server resources (especially with persistent connections, where the connection stays open between requests).

This boils down to the context of how PHP/MySQL was used back then:

• Most early PHP scripts were short-lived web requests—they handled a single user request, sent a response, and exited. PHP’s automatic resource cleanup took care of everything behind the scenes, so manual freeing was never needed.
• Early applications typically dealt with smaller datasets, so result sets didn’t consume enough memory to cause noticeable issues.
• The older mysql extension (predecessor to mysqli) had slightly different resource management, and server hardware/concurrency levels were much lower—so resource leaks rarely manifested as visible problems.

内容的提问来源于stack exchange，提问作者firashelou