Why PHP SpreadSheet doesn't free memory after writing to disk?

Question

I have a function, that write data and apply some style to an Excel file using PHPSpreadSheet (with Symfony):

use PhpOffice\PhpSpreadsheet\Writer\Xlsx as XlsxWriter;
function writeExcel(array $sheets_data, string $excel_path): void
{
    // Load pieces
    list($data_1, $data_2, , $data_3) = $sheets_data;

    // write data to excel
    // load template
    $reader = IOFactory::createReader("Xlsx");
    $spreadsheet = $reader->load('some_template');
    $sheet_1 = $spreadsheet->getSheet('first_sheet');
    $sheet_2 = $spreadsheet->getSheet('second_sheet');
    $sheet_3 = $spreadsheet->getSheet('third_sheet');

    // piece 1 style
    $sheet_1->fromArray($data_1, NULL_VALUE, 'A3');
    self::formatSheet1($sheet_1, count($data_1));

    // piece 2
    $years_count = count($data_2['values']);
    $appel_name_row = 13 + $years_count + 4;
    self::fillSheet2($sheet_2, $data_2, $appel_name_row);
    self::applySheet2Style($sheet_2, $years_count, $appel_name_row);

    // null presta
    $sheet_3->fromArray($data_3, NULL_VALUE, startCell: "A3");
    SdisData::formatSheet3($sheet_3, count($data_3), -1);

    $spreadsheet->setFirstSheetIndex(0);
    $spreadsheet->setActiveSheetIndex(0);

    // Write sheet
    $writer = new XlsxWriter($spreadsheet);
    $writer->save($excel_path);
}

Each time this function is called, it writes to each sheet between 20 and ~1000 rows.

My problem is, each time I call this function, it takes ~500mb of RAM, and even after the function has finished, memory isn't freed (It is problematic, as I have to call this function 1-120 times consecutively).

I tested it with this code:

$start = memory_get_usage();
self::writeExcel($pieces, $excel_path);
echo 'Memory increase: ' . (memory_get_usage() - $start);

Which outputs:

Memory increase: 509151792 (~510mb)
Memory increase: 509973088 (~510mb)
Memory increase: 537694520 (~540mb)

After trying multiple things, I realized that by removing the part where I write the file to disk (the last 2 lines of the function), memory is drastically less used, as my code outputs:

Memory increase: 14405696 (~14mb)
Memory increase: 12522072 (~12.5mb)
Memory increase: 1256720  (~1.2mb)

So my questions are, why is so much memory used when writing the SpreadSheet to disk, why is memory used only when writing to disk,and most importantly, how can I use less memory/free it?

EDIT: I modified the template that is loaded (by reducing the range to which style is applied), and now PHPSpreadSheet uses less memory - but still, it doesn't free it once it is done writing the file, which is a big issue for me.

Answer 1

Please be aware that PHPSpradSheet keeps a full PHP-representation of your excel-File in memory. Multiply cells * rows * formatting etc. to estimate a raw size.

You seem to load a template:

$spreadsheet = $reader->load('some_template');

How large is it? If you want to find out what's happening where go for xdebug , enable profiler and use qcachegrind to identify where time and memory are consumed.

My guess is that when you call $writer->save($excel_path); the template is loaded and your changes are applied.