When to call mysqli::close

问题:

When should i call mysqli::close? I never used to use if statements to check whether bind_param(), prep() and execute() were successful. Should I call $stmt->close() at the end of the method(below) . Or should I call it after every condition ensuring that I close the database connection even if the process fails at some stage e.g bind param.

public function function_name($id,$new_id ){
    $query = "UPDATE TABLE SET name = ? WHERE field = ? ";
    if($stmt=$this->prepare($query)){
        if($stmt->bind_param("is", $id, $new_id)){
            if($stmt->execute()){

            }else{//Could not execute the prepared statement
                $message = "Could not execute the prepared statement";
            }
        }else{//Could not bind the parameters
            $message = "Could not bind the parameters";
        }
    }else{
        $message = "Could not prepare the statement";
    }
    return $message
}

回答1:

When PHP exits it closes the database connections gracefully.

The only reason to use the close method is when you want to terminate a database connection that you´ll not use anymore, and you have lots of thing to do: Like processing and streaming the data, but if this is quick, you can forget about the close statement.

Putting it in the end of a script means redundancy, no performance or memory gain.

Whats is important: unset unused data, and if you will want to avoid memory leaks (which in my humble opnion are problem of PHP core in this case) use:

mysqli_kill();
mysqli_close(); 

This way the socket is killed too.

回答2:

You should always gracefully close the connection when you are done with it, to avoid performance and memory/handle leak problems. On the other hand, you should also make sure that you really are done with it - your script will crash if you try to use a closed connection.

The same goes for statements. If a statement is no longer going to be used, dispose of it appropriately.

回答3:

Just a little thought you could create another method called function_close and call it after you have called the function_name method.

This way if you change to pdo or mongo you will just have to refactor the methords rather than every instance of close.

回答4:

you should close it especially after a multi query (http://php.net/manual/en/mysqli.multi-query.php) because you could get memory problems. Otherwise closing is not needed.