PHP优化使用file_put_contents函数

Question

I'm querying the database and then storing returned data to XML file with file_put_contents(). I'm wondering which way of invoking this function is better. Note that $data is large array and variable $rss can contain a big string in this case.

At first I implemented something like this:

foreach($data as $item)
{
    $rss .= '<title>'.getTitle($item['id']).'</title>';
    $rss .= '<data>'.getData($item['id']).'</data>.';
    file_put_contents($this->fileRss, $rss);
    unset($rss);
}

And then I changed above to:

foreach($data as $item)
{
    $rss .= '<title>'.getTitle($item['id']).'</title>';
    $rss .= '<data>'.getData($item['id']).'</data>.';
}

file_put_contents($this->fileRss, $rss);

Which way is better? Making a big, big variable $rss and then saving it or saving quite small variable every time? I'm not sure but I think IO operations are slower than memory operations so first way is better. Only problem may be memory limit.

Answer 1

The first example is incorrect, unless you add FILE_APPEND to file_put_contents.

file_put_contents($this->fileRss, $rss, FILE_APPEND);

I would rather manually open the file before the loop, write each chunk of rss data inside the loop, and close the file after the loop.

$file = fopen($this->fileRss, 'w');
foreach($data as $item)
{
    $rss = '';
    $rss .= '<title>'.getTitle($item['id']).'</title>';
    $rss .= '<data>'.getData($item['id']).'</data>.';
    fwrite($file, $rss);
}
fclose($file);

This way you do not store all the rss entries in memory, and you avoid opening and closing the file in each iteration. I have also replaced the unset with $rss = ''; to avoid garbage collection inside the loop.