How can I write large PDFs quickly and efficiently using mPDF? - php

Question

I am updating an application using an old version of fPDF to the latest mPDF version 8.
My question is how to mitigate the much discussed slowness with HTML tables in mPDF.
The current fPDF code uses the Cell method and generates the PDF in less than a second.
By comparison, writing some simple HTML to use in mPDF generates a similar PDF in about 12-15 seconds.
My testing is with around 3500 records, but this can easily hit 10k records for some results.
Loading
I am loading the mpdf object like this;
$mpdf = new \Mpdf\Mpdf(array(
"tempDir" => "/tmp/pdf",
"mode" => "utf-8",
"format" => "Letter-P",
"margin_left" => "10",
"margin_top" => "10",
"margin_right" => "10",
"margin_bottom" => "10"
));
$mpdf->WriteHTML(file_get_contents("css/pdf.css"), \Mpdf\HTMLParserMode::HEADER_CSS);
$mpdf->simpleTables = true;
My css/pdf.css file
.cdrTable {
width: 25cm;
}
.cdrTable td {
text-align: center;
}
Writing
I've kept the HTML as simple as possible to prevent any auto-resizing issues.
Store this html in variable and write once using $mpdf->WriteHTML($html);
<h2>Results for this run</h2>
<p><strong>Sources are:</strong>
[pbx] From PBX
[sdc] From DC
</p>
Store a table of 50 records and write once using $mpdf->WriteHTML($html);
<table class='cdrTable'>
<tr>
<th>#</th>
<th>Call Started</th>
<th>Call From</th>
<th>Call To</th>
<th>Duration</th>
<th>Ext</th>
<th>Ext Label</th>
<th>Data Src</th>
</tr>
<tr>
<td>1</td>
<td>02-07-2020 04:52:39 PM</td>
<td>Polycom VVX601 [11]</td>
<td>Conference [86]</td>
<td>0:13</td>
<td>101</td>
<td>My Phone</td>
<td>pbx</td>
</tr>
.. Up to 50 records ..
</table>
Store this html in variable and write once using $mpdf->WriteHTML($html);
<table>
<tr>
<td>3555 records matched</td>
<td>Total: 1965:11</td>
</tr>
</table>
Finally
$mpdf->Output("reports.pdf", \Mpdf\Output\Destination::DOWNLOAD);
Conclusion
Outputting this to a browser is quick;
Peak Mem: 6.82 M, Time: 0.055243015289307
Generating the PDF is not so quick;
Peak Mem: 14.52 M, Time: 13.560908079147
I have tried writing 100, 200, 1000, and the whole result set at once without much difference in time.
Is there anything I can do to make this quicker?
Should I use something besides HTML tables or skip using HTML at all?