Opened 22 months ago

Last modified 22 months ago

#34356 closed Bug

Memory leak when generating PDFs — at Version 2

Reported by: Robin (Robert) Thomas Owned by: nobody
Component: Core (Other) Version: 4.1
Severity: Normal Keywords: memory memory-leak pdf weasyprint
Cc: Triage Stage: Unreviewed
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description (last modified by Robin (Robert) Thomas)

Context

Our app generates a one-page PDF report for users. It contains a few small SVG and PNG icons, and 4 big textual tables. The PDF is generated once, after which it is put in a storage bucket for subsequent retrieval.

Problem

The app is Django 4.1.6, Weasyprint 57.2, running on Heroku (heroku-22). We're not having any issues retrieving previously-generated PDFs, but each time it generates a new PDF (filesize 38kb) the app's memory RSS increases by 20 - 40mb, as reported by Heroku. This memory usage doesn't go down until the server is restarted.

Unfortunately Heroku doesn't automatically restart the server until both memory RSS and swap exceed the 512mb limit, so once RSS is used up we start getting a lot of pings about OOM errors and have to manually restart it.

What we've tried

Even after removing all images, fonts, and CSS (filesize 32kb) each generation still increases the memory RSS by about 17mb.

If we remove everything from the report template, leaving just <!DOCTYPE html><html lang="en"><head><title>Test</title><body></body></html> (filesize 863b), each generation increases the memory RSS by about 1.3mb.

I opened a bug ticket about this with Weasyprint (​https://github.com/Kozea/WeasyPrint/issues/1496). They say that because they cannot reproduce this when running just Weasyprint by itself from the command-line, the memory leak must be elsewhere in the ecosystem.

Reproduce

I deployed a little test app to show this in action, with a link to the source code: ​https://weasyprint-mem.herokuapp.com/

You can see from the attached image that every time a PDF is generated it increases the memory usage, although not always consistently. I would expect the data for each PDF to be garbage-collected once it has rendered:

https://code.djangoproject.com/raw-attachment/ticket/34356/219976184-2e826b19-eb1d-40a8-926a-b9751468f0eb.jpg

Change History (3)

by Robin (Robert) Thomas, 22 months ago

Attachment: 219976184-2e826b19-eb1d-40a8-926a-b9751468f0eb.jpg​ added

Screenshot of memory usage

comment:1 by Robin (Robert) Thomas, 22 months ago

Description: modified (diff)

comment:2 by Robin (Robert) Thomas, 22 months ago

Description: modified (diff)
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